CA1312809C

CA1312809C - Anti-theft sensor marker

Info

Publication number: CA1312809C
Application number: CA000582663A
Authority: CA
Inventors: Kiyotaka Yamauchi; Yoshihito Yoshizawa
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 1987-11-17
Filing date: 1988-11-09
Publication date: 1993-01-19
Anticipated expiration: 2010-01-19
Also published as: US4945339A; EP0316811A2; DE3855778D1; DE3855778T4; DE3855778T2; JP2713711B2; EP0316811B1; EP0316811A3; JPH01131995A

Abstract

Abstract of the Disclosure An anti-theft sensor marker is disclosed which has good sensitivity characteristics and which does not readily deteriorate due to bending stress. The marker is mainly composed of an alloy ribbon and is employed in an anti-theft system in which the stealing of a commodity previously marked by the marker is determined by detecting a magnetic field of a specific frequency with respect to an incident magnetic field intensity applied to a detection region through the alloy ribbon of the marker when the marker is disposed within the detection region.
The alloy ribbon has the constitutional formula (Fe1-aMa)100-x-y-z-.alpha.-.beta.-.gamma. wherein, M is at least one member selected from the group consisting of Co and Ni; M' is at least one member selected from the group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo; M" is at least one member selected from the group consisting of V, Cr, Mn, Al, platinum metals, Sc, Y, rare-earth metals, Au, Zn, Sn and Re; X is at least one member selected from the group consisting of C, Ge, P, Ga, Sb, In, Be and As;
and a, x, y, z, .alpha., .beta. and .gamma. satisfy the relations:
0?z?0.3, 0.1?x?3, 6?y?25, 3?z?15, 14?y+z?30, 1?.alpha.?10, 0?.beta.?10, 9?.gamma.?10, and wherein at least 50% of the structure of the alloy ribbon is composed of fine bccFe solid-solution crystalline grains in which the mean grain diameter, measured as a maximum grain diameter, is not larger than 500 .ANG..

Description

~312809 1 ANTI-l~P:FT SENSOR MARXER

Field of the Invention The present invention relates to an anti-theft sensor mark~r for use in an anti-theft sensor system in which, for exampla, a commodity of a store which has not been paid for, or a book in a library which i5 not allowed to be checked out of the library, is identified by q marker previously attached to the commodity or the book.
B~CKGROUND OF ~ ENTION
Heretofoxe, magnetism has been used in an anti-theft system to prevent, for example, the stealing of books from a library or c-ommodities from a department store (Refer to Japanese Patent Post-Examination Publication No. 58-53800 and U.S. Patent No. 4,510,489). In such a system, a marker having a width of 1-2 mm and being formed of an amorphous alloy thin ribbon is previously attached to every book or every commodity. In order to lawfully remove such a commodity or book~ for example, the commodity or book is delivered to a customer outside of a marker detector after a lawful procedure (i.e., paying for the commodity or signing out the book) is completed in a reception or adjustment office. On the other hand, a commodity or the like which is illegally or unlawfully ta~en out i9 detected through the marker previously attached to the commodity or the like by det~cting the magnetic field of a frequency having a harmonic relationship to the magnetic field of a specific frequency applied to a detection region set up at an entrance or exit. In short, the stealing of the commodity is checked.

~ - 2 - l 3~ 280q 1 Fig. 1 is a typical circuit diagram showing an example of the aforementioned magnetic anti-theft syste~. In the drawi~ng, the referen-e nume;al designates an oscillator for generating an AC current of a freguency f. The reference numeral 2 designates a notch filter formed to remove a specific frequency from the alternating current and arranged to transmit the AC current to an oscillation coil 4 through an amplifier 3. The reference numeral 5 designates a receiving coil. The receiving coil 5 and the . oscillation coil 4 form a detection r~gion 6. A
lock-in amplifier 7 and a signal processing circuit 8 - -are connected in series to the receiving coil 5.
According to the aforementioned construction, a specific harmonic component can be outputted through the lock-in amplifier 7 when, for example, the marker 9 is disposed within the detection region 6 to which an incident magnetic field Ha is applied, in the presence of a bias magnetic field Hb (the 20 . geomagnetisim). The specific harmonic componet thus outputted can be converted into a visible or audible signal ~: ~ through the signal processing circuit 8.
~: Accordingly, a wrongful act can.be easily exposed or prevented by connecting a patrol light or buzzer to the succeeding stage of the signal processing circuit 8.
. As another method, there is known an anti-theft system using a marker formed of an amorphous alloy thin robbon having a relatively large electromechanical coup ~ng coefficient, According to this system,. the marker is excited with an AC current :: .after being biased magnetically, so that the stealing : of the commodlty or the like can be detected through ~ ~ .
~:~ 35 ' _ _ , _ ; _ _ ._ __, _= . , .,, ,. . . _ __. .=_ . .. . .. . ....
.
: ~ ' _ 3 _ 1 3 1 2809 1 the presence of the marker by measuring frequencies of resonance and non-resonance.
Similar methods other than the aforementioned methods are known as anti-theft sensor system using a marker formed of an amorphous alloy thin rib~on. The mos~ important feature in these systems is that the soft magnetic alloy, used as the marXer, has excellent magnetic characteristics.- In other words, the requirement for the magnetic characteristics of the marker used in the anti-theft ser,sor system is as follows: (1) the magnetic permeabilit~ is large;

(2) the magnetizing curve is angular; and (3) the coercive force is relatively small.
Fig. 2 shows the dependence or relationship of the output vol~age on or with the incident naynetic field in the case where the mar~er, formed of a soft magnetic alloy, is present within the detection region 6 in the system of Fig. 1. In the Fig. 2, a designates a tertiary harmonic component (3f) and b designates a secondary harmonic component (2f). In the system, the value 2f-3f i5 detected so that the presence of the maker within the detection region can be identified. Accordingly, the detection sensitivity of the marXer increases as the area surrounded by the curve a and ~he x-coordinate axis increases relative to the area surrounded by the curve b and the x-coordinate axis.
Fig. 3 shows an example of the anti-theft sensor marker. In Fig. 3, the reference numeral 10 designates a soft magnetic alloy ribbon. the reference numeral 11 designates a first support member, for example, formed of paper, and the reference numeral 12 designates a second support .. . _ _ , _ ; . _ . . . _ _ _ = _ ._ _ = _ _ .. _ _ _ _, .. . . . . . .. . .. .. ._ _ 1 member, for example, formed of polypropylene. The soft magnetic alloy ribbon 10 is fixed between the support members 11 and 12 through an a~hesive agent.
In general, an adhesive agent is also applied to the rear surface of the member 11 so that the marker can be easily fixed to a commodity or the like.
The re~uirement for the characteristics of the soft magnetic alloy used in the marker i5 as follows:
(1) maximum magnetic permeability is large; (2) the angular rate of the magnetizing curve is large;

(3) the coercive force is relatively small; and (4) magnetostriction is small.
Per~alloy and amorphous alloy are known as soft magnetic alloys having the aforementioned character-isti_- (for -xample, as disclosed in Japanese Patent Post-Examination Publication No. 58-53800, Japanese Patent Unexamined Publication No. 58-39396, and the like). Almost all of the magnetic anti-theft sensor markers which have been put into practice employ one of the aforementioned soft magnetic alloys.
As described above, the prior art type anti-theft sensor markers have employed either ~` permalloy or amorphous alloy. However, in the case of permalloy, the soft magnetic characteristics ~, 25 deteriorate remarkably due to bending stress, and therefore the range of use is limited because the marker within the detection reqion cannot always be detected. On the other hand, in the case of amorphous alloy, the deterioration of the soft magne~ic characteristics dué to bending stress is considerably-less than that in the case of permalloy.
Accordingly, the use of amorphous alloy is superior to the use of permalloy in this respect. However, .

'~
i''''''''' ' ' _ 5 _ 1 3 1 28 ~

1 the soft magnetic characteristics of amorphous alloy as a marker is unsatisfactory. More particularly, in order to reduce the deterioraticn of the soft magnetic characteristics due to bending stress, amorphous alloy, in general, mainly contains Co and has a relatively small saturation magnetostriction constant(~S).
. As a result, the costs asssciated with the Co amorphous alloy are expensive.
Sum~ary of th~ Invention A_cordingl~, it is an object of the present invention to provide a novel anti-theft sensor marker which has excellent soft magnetic characteristics, which only undergoes a small amount of deterioration due to bending stres~, ~nd ~nich employs an-economical sot magnetic alloy ribbon to thereby solve the aforeinentioned problems in the prior art.
The present invention accomplishes these objects by providing an anti-theft sensor marker which is mainly composed o an alloy ribbon, and which is used in an anti-theft system in which the stealing of a commodity previously marked by the marker is detected on the basis of whether or not the marker is present by detecting a magnetic field of a specific 25 frequency with respect to an incident magnetic field intensity applied to a detection region through the alloy ribbon of the marker disposed within the detection region, the alloy ribbon having the constitutional formula l-aMa)loo X-y-Z-a-B y CUxSiyBzM t~M"BX y - (atomic %) (in which M is at least one member selected from the group consisting of Co and Ni; M' is at least one :
~ 35 :

.
, 1 member selected from the group consisting of -,~, W, Ta, Zr, Hf, Ti and Mo; M" is at least one member selected from the group consisting of V, Cr, Mn, Al, platinum metals, Sc, Y, rare-earth metals, Au, Zn, Sn and Re; X is at least one member selected from the group consisting of C, Ge, P, Ga, Sb, In, Be and As;
and a, x, y, z, a, 3 and ~ satisfy the relations:
OSa<0.3, O.l~x53, 6Sy<25, 3~zS15, 14~y~zS30, 1~<10, O<B~10, 9~ Y~10), at least 50% of the structure of the alloy ribbon - being composed of fine bccFe solid-solution crystalline grains in which the mean grain diameter, measured as a maximum grain diameter, i5 not more than 500 A.
~e~ause the alloy ribbon has goGd soft magnetic characteristics, a highly-sensitive anti-theft sensor marker can be obtained.
BRIEF DESCRIPTION OF 1~ DRAWINGS
Fig. 1 is a circuit diagram showing an example of a magnetic anti-theft sensor system;
Fig. 2 is ~n explanatory view of a method for measuring sensitivity;
Fig. 3 is a perspective view of the structure of a marker;
Fig. 4 is a schematic view of a method for producing the marker;
Fig. 5 is a view showing the X-ray pattern of an amorphous alloy;
Figs. 6(a) and 6~b) are views showing the X-ray pattern and microscopic grain structure of an alloy according to the present invention, respectively;
Fig. 7 is a graph view showing a B-H curve; and _ 7 _ 1312809 1 Fig. 8 is a graph showing the condition that the sensitivity ratio is deteriorated due to bending stress.
DETAILED DESCRIPTION OF T~ INVENTION
S In the present invention, Cu is one of the essential elements and the Cu content x is within a range between 0.1 and 3 atomic %. If the Cu content x is less than 0.1 atomic %, the effect of im~roving maximum magnetic permeability due to the addition of Cu cannot be expected. If the Cu content is more than 3 atomic %, maximum magnetic permeability may become small~r than that in the case where Cu is not added. In particular, the preferred Cu content x is within a range between O.5 and 2 atomic %. When the Cu content is within this range, màximum magnetic . permeability becomes larger to obtain an anti-theft sensor marker having high detection sensitivity.
In general, the alloy employed in the present invention can be prepared by the process for removing an amorphous alloy of the aforementioned constitution from a molten bath by quenching or by a vapor-phase quenching method, such as a sputtering method, a vapor deposition method or the like, and the heat-treatment process for forming fine crystalline grains by heating.
The cause of the improvement of maximum magnetic permeability depending on the content of Cu is unclear, but may be explained a~ follows.
Because the parameter of interaction of Cu and Fe is positive and, accordingly, the solid solubility o Cu and Fe is so low that Cu and Fe have a tendency o become separated from each other, Fe atoms or Cu atoms are gathered with the heating of an ~: 35 :
~; .
, :

, -`` 1312809 1 amorphous-state alloy to thereby form a cluster to produce constitutional fluctuation. For this reason, a large number of partly crystalline regions are formed and, accordingly, nucleated to produce fine crystalline grains. Because the crystals mainly contain Fe and because the solid solubility of Fe and Cu is small, Cu atom~ are swept out of the fine crystalline grains with the- advance of crystallization, so that the Cu concentratio~ in the peripheral regions of th~ crystalline grains increases. It is possible to consider that the crystalline grains are difficult to ~ow fcr this reason.
The formation of fine cxystalline grains may be caused ~y the fact ~hat a large number of crystal1ine nuclei are produced with the addition of Cu and the fact that the crystalline grains are difficult to grow. It is believed that this function is remarXably increased in the presence of specific elements, such as Nb, Ta, W, Mo, Zr, Hf, Ti and the like.
Without the specific elements, such as Nb, Ta, W, Mo, Zr, Hf, Ti and the like, fine crystalline grains are not sufficiently produced, so that the soft magnetic characteristics become poor.
Further, in the case of the alloy according to the present invention, a fine crystalline layer mainly containing Fe is formed, so that the magnetostriction of the alloy is smaller than that of Fe amorphous alloy. As the ma~netostriction decreases, magnetic anisotropy due to internal bending stress decreases. This is considered to be -~,, -`" 1312809 1 one of the reasons why the soft magnetic character-iStiC-Q are improved.
Without the addition of Cu, t~le crystalline grains hardly become fine. In this case, a compound layer is easiiy produced, so that the magnetic characteristics deteriorate due to crystallization.
Si and B are elements useful for the formation of fine grains and the adjustment of magnetostriction in the alloy. It is preferable that the alloy according to the invention is prepared by forming fine crystalline grains through heat treatment ater adding Si and B to form a~.orphous alloy. The reason for the limitation of the Si content y is as follows.
If y is more than 25 atomic %, the magnetostriction undesirably increases under ths yood condition of soft magnetic characteristics. If y is less than 6 atomic %, sufficient maximum magnetic permeability cannot be attained. The reason for the limitation of the B content z is as follows. If z is less than 3 atomic %, a uniform crystalline grain structure cannot be attained, 50 that the maximum magnetic permeability undesirably decreases. If z is more than 15 atomic ~, magnetostriction undesirably increases under the heat treatment condition suitable or good soft magnetic charactaristics. The reason for the limitation of the sum amount y+z of Si and B
is as follows. If y~z is less than 14 atomic %, non-crystallization is difficult, so that soft magnetic characteristics deteriorate. I y~z is more than 30 atomic %, there occur a remarXable decrease of satu-ration flux density, a decrease of maximum magnetic permeability and an increase of magnetostriction. It is preferable that the Si content and the B content " - 10- , 13l2~o9 1 satisfy the relations: lO~y~25, 3~z512 and 18Sy+~s28. When the Si contant an~ the B content satisfy the aforementioned relations, a low-1088 alloy having saturation magnetostriction of 5 x 10 6 or less can be easily prepared, so that the daterioration of the characteristics of t~e anti-theft sensor marker due to bending stre~s can be reduced.
It is preferable that the Si content and the B
content satisfy the relations: ll<yS24, 3~z59 and 18Sy+z<27. When the Si content and the B content satisfy the aforementioned relations, an alloy having a saturation magnetostriction between -1.5 x 10 6 and 1.5 x 10 6 and havl~g improved deterioration o soft magne'ic characteristics due to bending stress can be easily prepared.
In the alloy according to the present invention, M~ has the function of making the precipitated crystalline grains fine by the combination addition of M and Cu. M- is at least one member selected from th~ group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo. These eleme~ts, such as Nb and the liXe, have the function of rising the crystallization temperature of the alloy. On the other hand, Cu has - 25 the function of lowering the crystallization ; temperature through the formation of a cluster. It i8 possible to consider that the growing of the crystalline grains are suppressed by the interaction ;- of these elements and Cu to make the precipitated crystalline grains fine. It i8 preferable that the M- content a iS within a range: lSSlO. If ~ is less than 1 atomic %, maximum magnetic permeability decreases. If a is more than 10 atomic %, saturation l flux density decreases remarkably. Accordingly, the preferred range of a is 2~8. When a is within the aforementioned range, low-loss characteristics suited to the anti-theft sensor marker can be obtained.
The addition of M" effectuates rhe improvement of durability against corrosion, the improvement of magnetic characteristics, the adjustment of magnetostriction, and the like.
If M"'is more than 10 atomic ~, saturation flux density is remarkably lowered.
In the magnet corë according to the present invention, an alloy containing 10 atomic ~ or less of at least one element selected from the sroup of C, Ge, P, Ga, Sb, In, Be, As and the liXe can be used.
lS These elements are useful elements for non-crystallization. The addition of these elements together with Si and B effectuates the acceleration of non-crystallization of the alloy, and the adjustment of magnetostriction and Curie temperature.
Although the residual part mainly contains Fe except for impurities, Fe may be partly replaced by the component M (Co and/or Ni). The M content is O~aS0.3. If the M content is more than 0.3, magneto-striction increases or maximum maynetic per~eability decreases.
Although the alloy according to the invention is an alloy mainly composed of a bcc-structure iron solid solution, the alloy may include amorphous layers, compound layers of transition metals, such as Fe2B, Fe3B, Nb, and the like, Fe3Si regular layers and the like. -These layers often deteriorate the magnetic characteristics. In particular, the compound layers of Fe2B or the like are apt to .

- 12 - ~312809 l deteriorate the soft magnetic characteristics ~ccordingly, it is preferable that these layers be absent as much as possible.
The alloy according to the present invention is composed of hyperflne crystalline srains having the grain size o 500 A or less and which are uniformly distributed. In most cases, the alloy is particularly excellent in soft magnetic characteristics and has the mean grain diameter within a range betwaen 20 and 200 A.
It is possible to consider that the crystalline grains are composed of an Fe solid solution in which Si, B and the like are dissolved in the form of a solid. The alloy structure, except the fine crystalline grains, is mainly amorphous. If the ratio of the fine crystalline grains reaches 100%, the magnetic core according to the present invention ~ shows sufficiently high maximum ma~netic ; permeability.
It is a matter of course that the alloy may contain unavoidable impurities, such as N, 0, S and the like, Ca, Sr, Ba, Mg and the like as long as the necessary characteristics thereof are not too deteriorated, and that the constitution of the alloy modified as described above can be identified as the constitution of the alloy used in the anti-theft sensor marker according to the present invention.
The alloy used in the magnetic core according to the pre~ent invention can be prepared by any one of various methods, such as those of forming fine crystalline grains through heat treatment after - forming an amorphous-thin ribbon by a single-roll method, a double-roll method, a centrifugal guenching `:
~ 35 - 13 - 131280~

1 method or the like; those of crystallizing amorphou3 film through heat treatment after forr~ir~g the amorphous film by a vapor deposition method, a sputtering method, an ion-plating method or the like;
those of crystallizing amorphous line through heat treatment ater forming the amorphous line by a rotary liquid spinning method or a glass-coat spinning method; and the like. -Accordingly, the alloy according to the invention can appear in various forms, such as a line, a thir ribbon, a film and the like. In general, the form of a thin ribbon is most suitable for the anti-theft sensor marker.
The heat treatment carried-out for obtaining the magnetic core according to the invention ha~ the double p~rpose of decreasing internal bending stress and forming a fine crystalline grain structure to improve maximum magnetic permeability and to decrease magnetostriction.
In general, the heat treat~ent is ordinarily :;
carried out in vacuum or inert gas, such as hydrogen gas, nitrogen gas, argon gas and the like.
As occasion demands, the heat treatment may be carried out in an oxidizing atmosphere> such as in the air.
The temperature and time required for the heat treatment vary according to the form, size and constitution of the amorphous alloy ribbon. In general, it is preferable that the temperature and time are within a temperature range between 450C and 700C higher than the crystallization temperature and within a time range between 5 minutes and 24 hours.
The conditions of heating and cooling in the heat treatment can be suitably change~ if necessary.

. 1312809 1 The heat treatment may be separated into a plurality of stages to be carried out at the same temperature or at different temperatures or may be carried out in multi-stage heat-treatment patterns. Further, the heat treatmant of the alloy may be carried out in a magneti~ field generated by a direct current or an alternating current. By carrying out the heat treatment in the magnetic field, magnetic anisotropy can be establi~hed on the alloy. By carrying out the heat treatment while applying the magnetic field in parallel to the axis of the alloy ribbon, the B-~
~urve can be shaped angularly. In the case where the angular ratio is not smaller than 60%, and the maximum magnetic permeability is not smaller than 50,000, a highly-sensitive anti-theft sensor marker can be prepared.
It is unnecessary to apply the magnetic field at all times during the heat treatment. The period for the application of the magnetic ield can be suitably selected as long as the temperature in the period is lower than the Curie temperature Tc of the alloy.
With the progress of the heat treatment, the Curie temperature of the main phase of the alloy formed by the heat treatment gradually increases from the temperature of the initial amorphous alloy.
Accordingly, the heat treatment can be carried out in the magnetic field at a higher temperature than the Curie temperature of the initial amorphous alloy. By passing an electric current through the magnetic core or by applying a high-frequency magnetic field to t~e magnetic core during the heat treatment, the magnetic core can be heat-treated. In the case where the heat -treatment is carried out in the magnetic fieldJ the l heat treatment may be separated into a plurality of stages. By carrying-out the heat treatment while applying tension or compressing force, the magnetic characteri~tics may be adjusted more suitably.
The following method shows an example of an industrial method for producing an anti-theft sensor marker of a soft magnetic alloy according to the present invention.
In the method for producing an anti-theft 6en~0r ma~ker, the amorphous 2110y thin ribbon having the constitution of the invention and, for exam~le>
prepared by a single-roll method is taken up on a reel and then successively passed through the continuous heat-treatment step, laminating step, and cutting step by the method as shown in Fig. 4 to thereby produce an anti-theft sensor marker. In Fig. 4, the reference numeral 13 designates a reel, the reference numeral 14 designates an amorphous alloy ribbon, the reference numeral 15 designates a heat-treatment furnace, the reference numeral 16 designates a reel, for example, for supplying poly-propylene, the reference numeral 17 designates a reel, for example, for supplying paper, the reference numeral 18 designates cutting means, the reference numeral l9 designates anti-theft sensor marker articles, the reference numeral 20 designates ribbon feed rollers, and the reference numeral 21 designate~
adhesive-agent applying rollers.
Although the aforementioned producing method is an example of a method for producing the anti-theft sensor marker according to the present invention;
this method must be ~trictly managed so that the delicate heat-treated ribbon is not injured before -- 16 - I 3l 28 Oq 1 the ribbon is produced as an article. If protective materials or constituent members, such as paper, propyler.e and the like, of the maker are weaX in strength, the maker produced as an article by the aforementioned method may be injured.
In order to solve these problems, it is desirable that a coating layer, which is durable against the heat-treatment temperature, is applied to the surface of the alloy ribbon, for example, by metal plating or the like. By the application of the coating layer, considerable "staying power" is brought to the ribbon even though the ribbon has been heat-treated. Accordingly, injuries during or after the production of the a~ti-theft sensor marker can be remarXably reduced, thereby providing good results of the invention. For example, non-magnetic plating of Cu or the like is suitable for the metal plating. As occasion demands, magnetic plating of Ni or the.like may be employed or plating of magnetic alloy having semi-hard magnetic characteristics may be employed.
The anti-theft sensor marker according to the present invention can be widely used for various purposes insofar as the marker is mainly composed of a soft magnetic alloy suitably selected. Further, it is a matter of course that the same effect can be attained even in the case where the anti-theft sensor marker is combined with a semi-hard magnet for the purpose of repeated use.
The present invention will be described in more detail with reference to the- following examples, however, the invention is not limited thereto.
Exampl _ . _ ., . ,_, ~ _ = :. . , . _ . _ . _ . . ...
, . . . . -- _ 131~09 1 A ribbon with the width of 2 mm and the thickness of 15 ~m was prepared by a single-roLl met~od using a fusion containing 1% of Cu, 13.5% of Si, 9% of B, 3% of Nb and a residual part of Fe in atomic ratio. The X-ray diffraction of the ribbon was measured, and a halo pattern typical in amorpnous alloy as shown in Fig. 5 was obtained. It was apparent from the results that the ribbon was almos~
perfectly amorphous.
The amorphous ribbon was cut into the length of - 7 cm and then heat-treated in a magnetic field in an atmosphere of N2 gas. ~uring the heat treatment, the magnetic field of 800 A/m was applied in parallel to the axis of the ribbon. The heating speed was 10C/min. After the heating at 550~C for an hour, the ribbon was cooled to room temperature at the mean cooling speed of 2.5C/min.
After the heat treatment, the X-ray diffraction pattern of the ribbon was as shown in Fig. 6(a) in which a crystalline peak appeared. The ribbon was ohserved with a transmission electron microscope as shown in Fig. 6(b). It was apparent from Fig. 6(b) that a large part of the structure of the ribbon was composed of hyperfine bccFe solid-solution crystalline grains distributed uei~ormly and having the grain size of rom 50 to 200 A.
The B-H curve of the ribbon thus prepared was shown in Fig. 7. The magnetic characteristics of the ribbon were as follows. The coercive force Hc was 0.45 A/m, the maximum magnetic permeability ~m was 1609000, the saturation 1ux density Bs was 1.24T, and the angular ratio was 92%. The ribbon was p~t into the detection region 6 in the apparatus shown in .. i .........
. .

.

1 Fig. 1 to examine incident magnetic field dependence.
Secondary and tertiary harmonic components with respect to the frequency of the incident magnetic field were detected as shown in Fig. 2. From the curves as shown in Fig. 2, the ratio of the areas surrounded by the curves and the x-coordir.ate axis was calculated to judye whether the sensitlvity of the ribbon wa~ good. For comparison with the conventional samples, the sensitivity of amorphous $ (C70 5~eo 5Mn6 5Si13 5Bg) ard supermalloy of the same form was measured in the manner as descri~ed above.
The ratio of the sensitivi~y of the respective sample to the sensitivity of amorphous was shown in Table 1.
It is apparent from Table 1 that the-sen~itivity of the sam~le according to the present invention was very good compared with the sensitivity of conventional samples.

E~ample 2 A 2 mm wide and 20 ~m thick amorphous alloy ribbon containing 1% of Cu, 16.5% of Si, 6% of B and 3% of Nb in atomic ratio was prepared by a single-roll method. An approximately 5 ~m thick Cu layer was applied to the surface of the ribbon by electroless plating. After plating, the ribbon was cut into the length of about 7 cm and then heat-treated in a magnetic field. During the heat treatment, the magnetic field of 800 A/m was applied in parallel to the axis of the ribbon. After the heating at 530C for an hour, the ribbon was cooled to 280C at the cooling speed of 5C/min. After the ribbon was left at 280C for two hours, the ribbon ~- was further cooled to room temperature at the cooling .

) r r ~ ~ --1 speed of 2C/min. The structure thus prepared was the ~ame as shown in Fig. 6. The magr.etic characteristics of the ribbon were as follows. The saturation flux density Bs was 1.20T, the coercive force Hc was 0.96 A/m, the maximum magnetic permeabilit~ ~ was 100,000, and the angular ratio was 87%.
The sample according to the present inve~tion was compared with the conventional samples in the same manner as in Example 1. Further, in order to examine the deterioration of sensitivity due to bending stress, the ribbon was wound on a round bar of diameter D (mm). Then the ribbon was returned to the original linear state to examine the change of sensitivity. The results were shown in Fig. 8. It is appar~nt from Fig. 8 that the sensitivity of amorphous (c~ as a conventional sample defined in Example 1 was not satisfactory but the change of the sensitivity due to bending stress was little. The sensitivity of supermalloy (d) ~as not satisfactory and the deterioration of the sensitivity due to bending stress was considerable.
On the contrary, the sensitivity of the sample of Example 1 according to the present invention was very high. However, the sample of Example 1 was injured when it was wound on the 20 mm diameter round bar. It is possible to consider that the probability of injury decreases because the anti-theft sensor marker is, in practice, used in the form as shown in Fig. 3. However, it i8 difficult to use the sample of Example l when severe bending strass acts on the sample. On the other hand, the sensitivity of the sample (b) of Example ~ according to the present 1 invention was good and, at the same time, the deterioration of the sensitivity thereof due to bending stress was little. Thus, it is apparen~ that the sample (~) can be used as a very good anti-theft senscr marker.

E~ample 3 A plurality of 1.2 mm wide and 18 ~m thick amorphous alloy thin ribbons respecti~ely constructed as shown in Table 2 were prepared by a single-roll method. After the respective ribbon was cut into the length of 7 cm, one sample (H in Table 2) was prepared by heat-treating the ri~on while applying a magnetic field of 800 A~m in parallel to the axis of the ribbon. Another sample (HF in Table 2) was-prepared by heat-treating the ribbon ~ithout applying any magnetic field. The saturation flux density Bs, the angular ratio Br/Bs, the maximum magnetic permeability ~m the saturation magnetostriction constant ~ s, and the sensitivity ratio measurPd on the two kinds of samples were as shown in Table 2.
The structures thus prepared were the same as shown in Fig. 6(b). It is apparent from Table 2 that the sensitivity of the respective sample of Example 3 according to the present invention is good compared with the conventional samples. In particular, in the case where the sample has the angular ratio of 60% or more and the maximum magnetic permeability of 60% or more, an anti-theft sen~or mark~r having highest io sensitivity can be prepared.
E~ample 4 , - 21 - ~312809 1 A plurality of 1.2 mm wide and 18 ~m thick amorphous alloy thin ribbons respectively constructed as shown in Table 3 were prepared by a single-roil method. Samples were prepared in the same manner as S in Example 3. During the heat treatment, a magnetic fiel~ was applisd to the respective ribbon The structures thus prepared were the same as shown in ~ig. 6(b)-The typical magnetic characteristics, the saturation magnetostriction ~s ~. the sensitivity ratio, and the sensitivity ratio measured in the case where the ribbon is returned to the original linear state after being wound on a 50 mm diameter round bar were as shown in Table 3. It is apparent from Table 3 that the all samples according to the present invention have good sensitivity and, in particular, in the case where ~s is not more than ~5 x 10 6, the deterioration of the sensitivity ratio is remarkably little.
Exam~le 5 A plurality of 2 mm wide and 20 ~m thick amorphous alloy thin ribbons respectively constructed as shown in Table 4 were prepared by a æingle-roll method. The respective ribbon was cut into the length of 7 cm. Then the rihbon was heat treated in the same manner as in Example 3. The se~sitivity ratio in the ¢ase where the sensitivity of the amorphous ribbon of t~e same form (as deined in Example 1~ was considered to be 1 was shown in Table 4. It is apparent-from Table 4 that all of the samples according to the present invention have good sensi tivi ty .

~' '' ' ' ., ' .

1 3 1 280~

1 As described above in detail, the anti-theft sensor marker according to the present invention is excellent in sensitivity and suffer little deterioration of sensitivity due to bending stress.
Further, the marker has an economical merit, because the marker can be formed of an alloy which mainly contains Fe. Consequently, the industrial effect according to ths .invention is very large.

lS

~ " 1 31 2809 Table 1 Mater ial sens it -invention Fe73 . s~:UlNb3Sil3 . sBg 4 . 5 aPr tr Amorphous ( Co70 . sFeQ . sMn6 . ssil3, 5Bg ~

Supermalloy n . g ~ .

:::

~. :

--~4--'v~. o~ ~ ~ ~ ~ c -~ o ~ r~ ul _ ~7 ~
. ~ ~ Il^) r~) ~) ~ t''l N N ~i ~1 N N ~1 ~1 O O
~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ O C: O O O O O O O O O O O O O O O
O O O O O O O O O O O O O O O O O
E~ o o o c~ o o o o o o o o o o o o o ~ o Ln o ~0 a) In CO ~ ~ ~ ~ O O Ln U~ ~ ~
~i r-l N ~ r-- ~) ~1 ~1 O Cl~ _ _ _ _ N 0 N ~0 ~ OC\ N ~ ~0 N ~ N ~`J ~D ~r t~l O
_ ~1 Ci~ ~D ~0 C~ N G~ 0~ ~1 U~ ~ C~ ~ C;~ N

. P~ ~ O ~ ~i r I r-i O ~i N r-l N N ~! ~1 ~1 U') __ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ ~p ~r ~ ~7 u~ ~o ~;r ~ r~ In O ~ ~ ~ r~ w I~ ~
~) ~ ~ a~ a~ ~ 00 r` ~D ~1 N N ~ 11~ N r l ~1 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ~ E~ ~r ~D ~D ~D ~) U~ N ~1 ~ 00 t'` ~ ~ O CO N ~1 ~ _ N N ~ ~1 ~ O r-l N r~l N r-l r-l r-l O 1~ q' Ll-l ~ m ~ ~ ~ ,i ,~ ~ ~ ~ ~ ~ ,~ ~ ~ ,~ O ~i O
E~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ C
tc p: p: :~ p: P: t~ p: m ~ m ~ t~
' ~ _ _ _ _ _ __ _ _ _ __ ~ Ir) N O~
D~ n z z :~; ~ :~: g ~ Eo~ n u r~ ~ 1~l ~

o O . O m . .~, r ~ . J ~n E

~ ~ O~ ~ I~ _I 'r 1~ N I ,~1 ~1 O~ O~
a) Q) 1~3 Il) ~1) ~IJ a~ a) ~u a) o a) ~ ~u o o :~ l~i ~1 IL~ E4 1~4 1~4 ELl 1~, ILI ~ 14 1~ 1~ 1~, ~,) 1~ c~
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ,o~ _ _ _ _ _ _ _ _ _ .u o 0~ r~ l~ O N CO 0~ ~ r~) ~C) N ~'7 ,~ ~1 (~ ~ ~1 ~ N ~ ~ N e$l ~ ~ ~
aJo~ _ _ _ _ _ .~ _ ___ _ _ _ .~ I_ ~O ~ ~ ~ ~ ~ U~ In ~ In C~
. o ~ N ~`1 ~ S`l ~ ~) ~ ~r ~ f~ ~*
: u) nl _ _ _ _ _ _ _ _ _ _ _ .
O ~D 00 ~ O O Ul CO O O 1~ U~ ~D
x ~r ~r ~ ~ ~r In 1~3 ~ ~ ~1 O ~i _ + 1- + + + + + + _ ~ ~ i .

~ ~ ~ O ~ U~ O ~ O ~ ~ ~ ~
O ~1 N N ~1 -1 N ~1 ~i N r l ~ ~1 _ O O O O O O O O O O O O
. . a~ P:~ o o o o o o o o o o o o ~ _ _ _ _ _ _ _ _ _ __ _ E~ ~ ~ ~ c~ ~D O ~ r~ ~ o~ ~3 ~ t~
_ f`l ~1 ~i N t'~ ~ O O O ~ r-i ~i ~ ~1 ~ ~ ~J ~ ~ ~1 ~ ~ ~ ~ ~1 ~ ~ .a z m z z m~ z _~ ~ u~ i~ _, ~ m d~ .,1 ~ U~ .~-1 .,1 U~

a u ~ m ;m m ~m ~ ¦

.,, O . ~ o . ~n u~ u~ u~ ~ cn O Z Z Z C~ ~U~ ~0~ V U V V ~q ~
u tn o~ ~ ~ ~ ~ u~ u~ In ~ U~
O ~ O O O O _~ _, _, U7 a~ ~ ~ a ~ aJ r~ ,~ I~ l` I~ r~
h h h h 1~ h o aJ O o a) a) _ ~_ _ _ _ _ h h i 4 i~ i~ h _ __ _ _ _ _ _ _ _ _ _ _ , - : :
, --`" 1 31 ~809 Table 4 _ Components of alloy sensitivity (atomic %) ratio Fe71CulSil5BgNb3Til 3.8 Fe69culsilsB9w5vl 3.2 _ Fe69CulSil6B8M05Mnl _ - 4.1 Fe69CulSil7B7Nb5RUl 3.3 _ Fe7lculsil4BloTa3Rhl 2.9 Fe72CulSil~BgZr3Pdl 5.1 .
Fe72,sCu0.5sil4B9Hf3Irl 3.4 Fe7Ocu2sil6B8Nb3ptl 3.7 1~ . Fe70,5Cul,5Sil5BgNb5Aul 3.6 Fe71, 5Cuo, 5sil5B9Nb3znl 4 . 3 Fe69~5cul.5sil5B9Nb3Molsnl 4.4 Fe68.5Cu2,5Sil5BgNb3TalRel S.2 Fe70culsil5B9Nb3zrlAel 3 . 7 ..
Fe7oculsil5B9Nb3Hflscl 4.4 Fe70~ulsil5B9Hf3zrlyl 3.6 _ .
Fe71CulSil5BgNb3Lal 4.6 ¦FeL7CulSil7BgMo3Cel ¦ 9.1 ~;

'.

Table 4 (Continued) . ~
Components of alloy sensitivit~
~atomic %)ratio . .__ . _ . ... _ Fe67CulSil7sgw5Prl 3.9 . . __ Fe67culsil7B9TasNdl - 4.2 ___ _ _ .. __ Fe67CulSil7sgZr5sml . 3.6 , Fe67culsil6Blo~f5Eul 2~6 Fe68CulSil8BgNb3Gdl 3.2 _ ._ __ ._ .. __ Fe68CulSilgB8Nb3Tbl 1.9 . _ _ . __ ____ . . __ . Fe72culsil4B9Nb3Dyl - 2.8 ._ . _ . _ _ Fe72culsil~B9Nb3Hol 5.0 Fe7lculsil4B9Nb3crlTil 3.2 .. __ . . ..
( Feo, 95Cuo . 01 ) 72culsil4B9Nb3crl . ' 2 . 8 O . 95CUO. 05 ) 72culsil4B9Ta3Rul 4 . 5 (Feo.gCuO.l)72CulSil4BgTa3Mnl 4.3 (Feo.99Nio~ol)72culsil4BgTa3Rul 4.2 - . .
: ~E~eo.g5Nio.o5)7lculsil4BgTa3crlRul 3.6 _.
;~: (FeO.gONiO.l)68culsil5Bgw5TilRul 3.3 ,. ~
: (Feo.sscoo.o3Nio.o2)~s.sculsil3.sBs~scrlRhl 2.7 . . .. _ (Feo.s~Co.olNio.ol)67culsilsBg~5Ru3 4.6 ;~
;'~

~':

. . ~ ~, . . .

Table 4 (Continued) raet I i t i V~ ~y Fe73culsil3B9Ni3cl _ ¦ 3 . 6 Fe73culsil3B9Nb3Gel j 4 . a Fe73Cu1Sil3BgNb3Pl ~ 3. 7 Fe73Cu1Sil3BsNb3Gal _ 2 . 8 Fe73culsil3BgNb3sbl 1 -Fe73Cul Sl l 3BsNb3As 1 3 - 3 Fe71CulSi13B8M05C2 5 . 2 Fe70Cu1Si14B6Mo3Cr1C5 ~ 4 . 3 (Feo.ssCoO os)70CulS1l3BsNbsAelC1 4~5 ~6 Fe68 . 5Cu1 . 5sil3BsNbsRulc2 ¦ 2 . 8 Fe70CulSil4B8Ta3Ru2C1 1 3 . 3 Fe68CulSil5BgNb5MnlBe1 4 .1 e6gCu2Sil4B8ZrsRhlIn~

Fe7lcu2sil3B7HfsAul 1 _ 3. 6 Pe~j6CulSil6BlOMo5SclGel I
Fe67. 5Cuo. 5sil4BllNb5 e 6 7Col S i 1 3B1 2Nb5LalGAI __ Table 4 (Continued) Components of alloy¦sensitivity ~atomic ~) ratio (Feo~95Nio.o5)67culsil3B9Nb5smlsbl 2.9 (Feo.92coo.o8)7oculsil3B9Nb5zn5Asl - 3.1 (Feo.96Nio.o2coo~o2)7oculsil3B9Nb5snlInl - 3.6 Fe69CulSil3BgMO5Relc2 4.1 Fe69CulSil3BgMOsc~lc2 2.8 Fe69CulSil3B9W5Prlc2 3.7 .

Fe69CulSil3B9W5Nblc2 _ 2.9 Fe68CulSil~BgTa5GdlC2 3.6 Fe69culsil3B9Nb5Tblc2 4.3 Fe7oculsil4B8Nb5DylGel 3.7 Fe72culsil3B7Nb5pdlGel 2.6 Fe7oculsil3B9Nb5Irlpl 5.3 Fe7oculsil3B9Nb5oslGal 2.9 Fe71CulSil4BgTa3Crlcl 4.5 Fe67culsilsB6zrsvlc3 _ 4.2 Fe63CulSil6B5Hf5Cr2c8 3.7 Fe68CulSil4BgMO4ru3cl 2.9 . _ .
Fe70CulSil4B4Mo3TilRulCl 2.8 pe67culsil4Bs3b6~h~c~ ¦ 3-3

Claims

1. An anti-theft sensor marker mainly composed of an alloy ribbon and employed in an anti-theft system in which the unlawful taking of a commodity marked by said marker is determined by detecting a magnetic field of a specific frequency with respect to an incident magnetic field intensity applied to a detection region through said alloy ribbon of said marker when said marker is disposed within said detection region, said alloy ribbon having the constitutional formula (Fel-aMa)100-x-y-z-.alpha.-.beta.-.gamma. wherein, M is at least one member selected from the group consisting of Co and Ni; M' is at least one member selected from the group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo; M" is at least one member selected from the group consisting of V, Cr, Mn, Al, platinum metals, Sc, Y, rare-earth metals, Au, Zn, Sn and Re; X is at least one member selected from the group consisting of C, Ge, P, Ga, Sb, In, Be and As;
and a, x, y, z, .alpha., .beta. and ? satisfy the relations:
0?a?0.3, 0.1?x?3, 6?y?25, 3?z?15, 14?y+z?30, 1?.alpha.?10, 0?.beta.?10, 9???10, and wherein at least 50% of the structure of the alloy ribbon is composed of fine bccFe solid-solution crystalline grains in which the mean grain diameter, measured as a maximum grain diameter, is not larger than 500 .ANG..

2. The anti-theft sensor marker according to claim 1, wherein at least part of the surface of said alloy ribbon is provided with a coating layer thereon.

3. The anti-theft sensor marker according to claim 2, wherein the coating layer is a magnetic alloy having a semi-hard magnetic characteristic.

4. The anti-theft sensor marker according to claim 2, wherein the coating layer is one of Cu and Ni.

5. The anti-theft sensor marker according to claim 1, wherein the angular ratio of the direct-current B-H curve of said alloy ribbon is not less than 60%; and wherein the maximum magnetic permeability thereof is not less than 50,000.

6. The anti-theft sensor marker according to claim 1, further comprising first and second support members, said alloy ribbon being sandwiched between said members.

7. The anti-theft sensor marker according to claim 6, wherein said first support member consists of paper, and wherein said second support member consists of polypropylene.

8. The anti-theft sensor marker according to claim 1, wherein said crystalline grains are uniformly distributed.

9. The anti-theft sensor marker according to claim 1, wherein the mean grain diameter of said crystalline grains ranges between 20 and 200 .ANG..

10. The anti-theft sensor marker according to claim 1, wherein the alloy is in the form of a line.

11. The anti-theft sensor marker according to claim 1, wherein the alloy is in the form of a film.

12. The anti-theft sensor marker according to claim 1, wherein the saturation magnetostriction .lambda. s of said alloy ribbon is not larger than +5 x 10-6.

13. The anti-theft sensor marker according to claim 12, wherein the saturation magnetostriction .lambda.s of said alloy ribbon ranges between -5 x 10-6 and +5 x 10-6

14. The anti-theft sensor marker according to any one of claims 1 to 8 or 10 to 13, wherein the mean grain diameter of said crystalline grains ranges between greater than 20 and not larger than 500 .ANG..