US3614339A

US3614339A - Magnetic transducer with wear resistant pole tips

Info

Publication number: US3614339A
Application number: US23157A
Authority: US
Inventors: Robert A Schneider
Original assignee: Spin Physics Inc
Current assignee: Eastman Kodak Co
Priority date: 1970-03-27
Filing date: 1970-03-27
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19

Abstract

A composite magnetic transducer head for operation at frequencies in the megahertz range having pole tips made of specially fabricated laminations formed from ingots of fusion cast or sintered iron-silicon-aluminum alloy.

Description

m u t it r it States 1 t1 Inventor Robert A. Schneider Del Mar, Calif. App1.No. 23,157 Filed Mar. 27, 1970 Patented Oct. 19, 1971 Assignee Spin Physics, 1111c.

San Diego, Calif.

MAGNETIC TRANSDUCER WITH WEAR RESISTANT POLE TIPS 5 Claims, 8 Drawing Rigs.

US. Cl 179/ 100.2 C, 29/603 lint. Cl G1 1b 5/412, G1 lb 5/14,G1 lb 5/22 lField of Search 179/ 1 00.2

C; IMO/174.1 F; 346/74 MC; 29/603 [56] References Cited UNITED STATES PATENTS 2,861,135 11/1958 Rettinger 179/100.2C 2,992,474 7/1961 Adams et a1. 179/1002 C 3,499,214 3/1970 Schneider 29/603 OTHER REFERENCES Magnetic Materials in Electrical Ind. P.R. Bardell- 1960, MacDonald & Co. Ltd., London. pg. 96 LC. 0T1 453B3 Primary Examiner-Terrell W. Fears Assistant Examiner-.1 ay P. Lucas Attorney-Hill, Sherman, Meroni, Gross & Simpson ABSTRACT: A composite magnetic transducer head for operation at frequencies in the megahertz range having pole tips made of specially fabricated laminations formed from ingots of fusion cast or sintered iron-silicon-aluminum alloy.

MAGNETI'IC NSDIJCER wrm we assist" more it:

BACKGROUND OF THE INVENTION The fabrication of composite instrumentation heads is dealt with in my prior US. Pat. Nos. 3,417,209 and No. 3,417,386 both dated Dec. 17, 1968. These patents disclose solid pole tips for composite heads which are formed of a cast alloy material known as sendust. There are numerous statements in the prior art to the efi'ect that sendust cannot be machined by conventional methods. See for example US. Pat. No. 2,988,806, column 1, lines 19-31 and column 5, lines 1-4, and US. Pat. No. 2,992,474, column 2, lines 5449. So far as presently known, heads utilizing an iron-silicon-aluminum material in the as-cast condition have always utilized a solid pole tip configuration such as shown in my prior patents. The concept has been to utilize pole tips of small dimensions so as to minimize the detrimental effects thereof at high frequencies.

be fabricated with a thickness of 10 mils (l mil-0.001 inch), there is no suggestion in the known prior art that such plates of sendust with a thickness of not more than about 0.2 mm. (approximately 8 mils) would be sufficiently smooth and flat to enable the production of laminated pole tips with uniform clearance therebetween of less than 300 microinches l microinch=0.000 l inch), so as to provide a laminated pole tip configuration.

Indeed in developing the head of the present invention it was found that laminations of the desired thinness (about mils) tended to curl and exhibit a potato chip effect. Further after annealing, the surface roughness increased by to 100 times, so that the laminations when placed at the required nominal separation (about. 200 microinches) had electrical contact with each other. Elaborate and extensive experiment was required to develop techniques for overcoming these effects and to develop a composite head with iron-silicon-aluminum pole tips exhibiting markedly improved highfrequency response in comparison to prior composite heads with solid sendust pole tips.

SUMMARY OF THE INVENTION This invention relates to an improved composite magnetic transducer head capable of handling frequencies in the megahertz range and to specially fabricated laminations and pole tip configurations for such a head, and to a method of manufacturing the same.

In the head construction of the present invention, the pole tips even though made of an extremely hard material, specifically a cast iron-silicon-aluminum alloy having a hardness of at least Rockwell (3-40, have been successfully formed into a laminated configuration which is particularly advantageous for composite heads operating in the megahertz frequency range.

It is therefore an important object of the present invention to provide an improved composite magnetic transducer head construction providing substantially better overall operating characteristics than prior art composite heads.

It is a further object of the present invention to provide a composite magnetic transducer head providing a laminated pole tip configuration of greatly improved gap stability and uniformity during a substantially increased useful life.

Further objects and features of the present invention relate to an improved lamination and an improved pole tip configuration, and to methods and techniques for economically fabricating the same, with commercially acceptable yields, and for reliably and conveniently producing a composite magnetic transducer head meeting desired frequency characteristics.

The laminated tip head of the present invention provides a frequency response characteristic which is much less affected by head wear; also the head inductance is readily controlled to match any desired system requirements. With the solid sen- While certain prior art documents suggest that sendust can dust tip head the length of the front gap between the ferrite core parts is very critical and the frequency response characteristics of the head change drastically with wear (necessitating annoyingly frequent circuit adjustments in use of the head). With the present laminated tip head the ferrite front gap can be widened substantially {c.g. by 5 mils) without the head high-frequency response falling below existing specifications.

Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be efiected without departing from the spirit and scope of the novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 11 is a partial somewhat diagrammatic top plan view of a head assembly in accordance with the present invention;

FIG. 2 is a partial side elevational view of the head of FIG.

FIG. 3 is a somewhat diagrammatic vertical sectional view taken generally along the plane represented by the line Ill-III in FIG. 1 and looking in the direction of the arrows, but illustrating the head assembly prior to completion of certain of the fabricating steps;

FIG. I is a somewhat diagrammatic longitudinal sectional view taken generally along the line lV-IV of FIG. 3 and illustrating in detail only the left half of the partially fabricated head assembly, a portion of the right half of the head assembly being indicated in dot-dash outline;

FIG. 5 is an enlarged somewhat diagrammatic longitudinal sectional view illustrating the pole region of the completed magnetic head assembly of FIG. 1 and! 2 and showing the path of a tape record medium thereacross;

FIG. 6 is a flow diagram setting forth certain principal steps in the method of forming pole tips for the head of FIGS. 1-5 from a commercially available ingot of fusion cast iron-siliconaluminum alloy;

FIG. 7 is a somewhat diagrammatic top plan view illustrating the arrangement for carrying out the lapping operation of step number 3 of FIG. 6; and

FIG. 8 is a somewhat diagrammatic vertical sectional view taken generally along the plane represented by the line Vlll-Vlll in FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1 and 2 is illustrated a magnetic transducer head formed of a pair of head subassemblies ll and 112. FIG. I shows a plan view of the tape confronting surface of the head which is formed by tip plates 13 and M, the top edges of shields -19 and the pole tips of transducer head units 211-24. The coupling gaps for the respective head units are indicated at 25-28 and are arranged to coincide with the interface between the head subassemblies II and 12.

For the sake of diagrammatic illustration, a magnetic tape record medium is indicated at 30 in FIGS. 2 and 5, having a flexible nonmagnetic backing 31 and a magnetizable layer 32 which is in sliding contact with the surface of the head assembly 10 as represented in FIG. 5. As shown in FIG. 5, the magnetic tape record medium 30 moves in the direction of arrow 33 across the

pole tips

34 and 35 of each of the head units. Ferrite core parts are partially indicated at 36 and 37 in FIG. 5, and a complete core part 36 is shown in FIG. 4. The

core parts

36 and 37 have converging faces 36a, 37a, FIG. 5, which define a front nonmagnetic gap 38, and have parallel confronting faces 36b, 37b, FIG. 4, defining a back nonmagnetic gap.

FIGS. 3 and 4 show the head subassembly 11 prior to completion of certain of the fabricating steps. For ease of reference, however, corresponding reference numerals have been applied to the parts in FIGS. 3 and 45 which correspond to those in FIG. 1 and 2, even though certain of the parts such as the tip plate 13 as shown in FIGS. 3 and 4 will receive further machining operations prior to completion of the head as shown in FIGS. 1 and 2. Referring to FIGS. 3 and 4, it will be observed that the core sections such as 36 receive respective transducer windings such as those shown at 41-44 in FIG. 3. The configuration of each of the head units 21-24 may be identical.

A mounting means for the ferrite core parts and shields comprises mounting brackets 46 (FIGS. 3 and 4) and 47 (FIG. 2), having interior walls such as 46a, 47a, FIG. 5, defining mounting slots for receiving the

ferrite core parts

36 and 37. In forming the subassembly ll of FIGS. 3 and 4, the core parts 36 are secured in the recesses of the associated bracket 46 by a suitable cement. The edge faces 360 of ferrite core parts 36 are lapped flat with lands such as indicated at 49, FIG. 3, at each side of bracket 46.

A coating of cement is then applied to each ferrite core edge face 36c, and to each bracket land area as 58, FIG. 2, 49, FIG. 3, and 53, FIG. 4. The tip plate 13 is applied with sufficient pressure such that the cement bonds to the lower edges of the pole tip laminations and forms an electrical insulating layer 50 of controlled thickness, for example about 20 to 40 microinches. The excess cement is squeezed out from between the confronting surfaces of the ferrite core parts and the respective pole tips and into the intervening spaces such as indicated at 51. The bracket 46 is shown with the land areas 49, FIG. 3, and 53, FIG. 4, spaced from the tip plate 13 by

cement layers

52 and 54 which are substantially equal in thickness to the layer 50. The insulating and

bonding layers

50, 52 and 54 appearing in FIGS. 3, 4 and 5, and corresponding layers such as 55, FIG. 5, and 56, FIG. 2, of the other head subassembly 12 are shown with exaggerated thickness in the drawings for the sake of clarity. The pressure and/or temperature applied.

to the bonding layers such as 50, 52, 54, 55 and 56 during the formation thereof may be selected to control their thickness dimension.

It has been found that the bonding layers 50 and 55, being electrically nonconductive in comparison to the conductivity of the ferrite edge faces 36c and 37c, provide electrical isolation of the laminations of each pole tip assembly, and result in improved high-frequency response where the

core parts

36 and 37 are of a manganese zinc ferrite having a resistivity of the order of 1000 ohm-centimeters or less.

The interior spaces such as 51, FIG. 3, and 59, FIG. 4, between the undersurface 13a of the tip plate 13 and an upper surface 46b of bracket 46 may be filled with a suitable epoxy supplied at apertures such as 60, FIG. 4, as described in my US. Pat. No. 3,4 I 7,209. The head subassembly 12 is provided with similar apertures such as 61, FIG. 2, so that spaces such as 62, FIG. 2, are likewise filled with epoxy which secures tip plate 14 to bracket 47. The further processing steps of the head subassemblies may conform with those disclosed in my prior patent.

The shields 15-19 are seated in recesses such as indicated at 64, FIG. 3, and may be bottomed against shield stops such as 65, FIGS. 3 and 4, for convenient positioning thereof during mating of the subassemblies 11 and 12. After the parts 1 1 and 12 are assembled, the empty spaces within the assembly are filled with a suitable potting compound, and the tape contacting surface is fonned as indicated in FIGS. 1, 2 and 5.

By way of example, the gaps 25-28 between pole tips such as 34 and 35, FIG. 5, of head units 21-24, may each have a length dimension of about 30 microinches for use as a playback head, and may have a length dimension of about 80 microinches for use as a record head. The confronting polar faces of

pole tips

34 and 35 may have a depth or vertical dimension as viewed in FIG. 5 of about 35: mils, (1 mil equals 0.001 inch), and the pole tips may each have a length of about 0.32 inch for a playback head and about 0.15 inch for a record head. The front gap 38 between the ferrite core parts may have a length dimension of the order of 3 mils. (In each case the length dimension is generally parallel to the direction of movement of the tape record medium.)

EXAMPLES OF LAMINATION FABRICATION TECHNIQUES Referring to FIG. 6, the basic steps in an exemplary method for fabricating laminations from the commercially available fusion cast material known as sendust are identified by numerals l-9. The following numbered sections will refer to these respective basic steps.

l. Sendust is commercially available in ingots, for example of lA-inch diameter and 6 inches long. A typical example of such commercial alloy has a composition of 84.5 percent iron, 6 percent aluminum and 9.5 percent silicon and a mechanical hardness of Rockwell C42. The stated characteristics are as follows: density 7.1 grams per cubic centimeter, and electrical resistivity micro-ohm centimeters.

The ingots are cut into bars 1 inch wide and 0.350 inches thick, and as long as possible, for example by an abrasive grinding technique using a silicon carbide wheel.

2. It is found that such bar material can be sliced into wafers having a thickness of 8 mils (0.008 inch) by means of a Norton Wafering Machine, which is known per se in the semiconductor art. For the present application, an aluminum oxide slurry is flowed over the blades of the machine which operate to progressively wear away material during a very large number of successive passes adjacent an edge of the bar. Thus, each bar is progressively sliced into a large number of wafers which when viewed in side elevation are of rectangular configuration with a length dimension of 1.00 inch and a height dimension of 0.350 inch. When viewed in a particular orientation, each wafer may be provided with a beveled upper left-hand edge which serves to provide a reference mark during subsequent processing. The bars formed in step number 1 may be provided with a suitable 45 chamfer along one of the long edges thereof so that the wafers are then formed with the beveled edge. (As an example, a bar of pole tip material as formed in step number 1 may have a long dimension of 4 inches).

3. The wafers as formed in step number 2 are then subjected to a single surface lapping operation which serves to reduce the thickness of the wafers to the desired ultimate lamination thickness, for example between 5 and 6 mils. It is found that such lapping can be effected utilizing aluminum oxide as the lapping compound and utilizing a Meehenite cast iron plate or a hard steel plate. Further details of the lapping procedure are given hereinafter having reference to FIGS. 7 and 8 of the drawings.

4. The pole tip wafers are then placed between aluminum oxide plates (0.1 inch thick) with weights on top of the aluminum oxide plates to tend to prevent curling or the "potato chip effect during an annealing operation. As indicated in FIG. 6, the annealing operation may take place at l000 C. for 5 hours, with cooling thereafter at the rate of 50 C. per hour until the temperature is reduced to 350 C. or 400 C., (which is below the Curie temperature of 482 C.). The material can then be forced cooled. 1

It is found that the pole tip wafers after annealing developed very substantial surface roughness, which is believed to be due to crystal shift during the annealing process.

5. It is found possible to effectively remove this surface roughness by subjecting the pole tip wafers to a further lapping operation to remove surface irregularities, and then subjecting the pole tip wafers to a second annealing operation which may be identical to the first annealing operation just described. It is found that the surface roughness does not again develop after the second annealing operation, and that the pole tip wafers now remain essentially flat and smooth with microinch overall flatness and a surface finish of 4 microinches R.M.S.

With the resultant pole tip wafer arranged with the beveled edge at the upper left as before, the opposite surfaces of the wafer are inspected over a zone between 20 and 60 mils below the upper edge to insure that this critical zone is free of pits greater than 0.0002-inch diameter (except adjacent the opposite vertical edges of the pole tip wafer).

Without the second annealing operation, it was found that the commercially available material developed such roughness that a stack of laminations with spacing of 200 microinches developed short circuits because of the surface roughness.

6. The flat and smooth pole tip wafers as formed in step number 5 are then stacked to form a wafer lamination assembly having a length dimension of 1.00 inch, and a height dimension of 0.35 inch and having, for example nine laminations with interposed cement layers. by way of example, the pole tip wafers may be sprayed or coated with a semirigid epoxy system and stacked in a fixture with accurate spacing. A hydraulic press with heated platens then compresses the stack to the proper width dimension with the excess epoxy being squeezed out from between the laminations and a strong mechanical bond being formed between the successive laminations of the stack to form a unitary structure, the bonding layers having a thickness of about 0.0002 inch (200 microinches) and less than 0.0003 inch (300 microinches).

7. The stack as formed in step number 6 is then double surface lapped to provide the desired stack width, for example 0.0503 inches plus or minus 0.0001 inch where the pole tip wafers had a thickness of 0.0056 plus or minus 0.0002 inch.

The wafer lamination assembly as thus formed is edge lapped along the long (1.00 inch) upper edge face to remove edge roughness.

8. Where recording pole tops are to be formed, the wafer lamination assembly with the orientation just described is cut horizontally and the cut edges lapped to provide two wafer lamination assemblies each having a height dimension of 0.155 inch and a lapped edge face which is perpendicular to the side surfaces thereof.

9. The wafer lamination assemblies are then cut into pole tip sections having a depth dimension of 0.014 inch plus or minus 0.002 inch, with an edge face having a width dimension of 0.0505 inch and depth dimension of 0.014 inch being formed from the lapped surface of the wafer lamination assembly so as to provide a gap defining face of the pole tip. Each pole tip section is inspected for a distance of 0.06 inch from the lapped gap defining edge face to be certain that no voids or pits greater than 0.0002inch diameter can be seen at the side surfaces of the pole tip section.

FIGS. 7 and 3 illustrate a suitable lapping apparatus 70 for carrying out step Nos. 3 and d. The lapping plate '71 is shown as rotating in the direction of arrow 71?; on a central vertical axis. Four retaining rings Id- 77 have external gear teeth (not shown) meshing with a central gear 7h which is selectively engagcabie to rotate with the lapping plate Til as indicated by arrow 79. When the gear 7% is engaged, the retaining rings are driven clockwise, while when the gear 7% is disengaged, frictional contact of the rings "I' l-7'7 with the surface of the lapping plate 7i drives the rings in the counterclockwise direction. The reversing of the direction of rotation of the rings I' l-7'7 is effected as necessary to maintain the surface of the lapping plate substantially flat.

The four retaining rings such as M are held in place on the lapping plate ll during a lapping operation by means of four air cylinders (not shown) fixed to the upper frame of the apparatus and having respective piston rods such as indicated at hi, FlG. ti, carrying universally mounted pressure plates such as m which fit within the respective rings such as M.

in the illustrated embodiment, the wafers such as 0 are carried in conforming apertures such as 85a of circular work holdem such as 05. Circular disks 67-90 are secured to the op surfaces of the respective work holders. The weight of the disks plus the pressure exerted by the cylinders may be such as to produce a pressure on the surfaces of the wafers such as 04 and as which engage the lapping plate of 6 pounds per square inch.

As indicated in H6. 0, the thickness of the holder plate 85 may be 4 mils, in comparison to an original thickness dimension of the wafers of 8 mils. There may be 22 apertures such as @511 disposed in a radial pattern as indicated diagrammatically at M in FIG. '7.

The wafers can be loaded into each work holder while the work holders are inverted. if the wafers are wetted with the slurry used during lapping prior to insertion thereof into the apertures of the work holder, surface tension will retain the waters in the apertures as the holders are placed on the lapping plate 711.

The slurry may comprise aluminum oxide particles with a size of 25 microns. One pound of the particles is mixed with 1 gallon of a suitable lapping oil such as Speedfam lapping oil supplied by Speedfam Corp, North Third Avenue, Des Plaines, Ill. The slurry is supplied in advance of each retaining ring at a rate of a couple of drips per second.

The wafers are lapped for about 2 minutes on one side and then inverted. This cycle is repeated about three time so that the total processing time for each group of lid wafers is about 12 minutes.

The lapping plate Ill may be rotated at about 50 revolutions per minute.

in the double surface lapping operation of step No. 7, lapping plates engage the stacks on each side of the work holders. A slurry may be formed using aluminum oxide particles of 3 microns, and a mixture of 1 pound of particles per gallon of the same lapping oil as before. About 10 minutes is required for this lapping operation.

The broad teachings of the present invention are also ap plicable to ingots of sintered silicon-aluminum-iron alloy having a thickness initially of at least about 20 mils and having a mechanical hardness of at-least Rockwell C- lO. For example, one sintered silicon-aluminum-iron alloy of approximately sendust composition has a mechanical hardness of Rockwell C-48, 21 resistivity of approximately 2.00 micro-ohm centimeters, a coercive force from saturation of 0. 10 oersted, a suture tion induction of ,9000 gausses, and initial and maximum permeabilities of 6500 and 25000, respectively. The concept in the prior art has been to sinter compacted masses of such alloys having essentially the desired ultimate thickness. Following the teachings of the present invention, blocks or bars of the sintered material can be formed and then watered and lapped as taught herein to provide laminations with a thickness of about 5 to 6 mils, and having much greater density and better magnetic properties than laminations heretofore available from this material.

In the case of one particular sintered alloy, an ingot 2 inches in diameter and 2 inches long was formed, having a Vickers hardness of the order of 700 (with 300 gram loading) in comparison to a Vickers hardness for a fusion casting of the conventional sendust material of about .500, (sendust having a Rockwell hardness of about CZ-42). This sintered alloy had a resistivity of about to l 10 micro-ohm centimeters and was wafered and lapped as taught herein to provide a lamination thickness of about 5%: mils. The wafers were annealed in a vacuum furnace by raising the temperature of the heating chamber from room temperature to 800 C in from one-half hour to l hour, and then shutting off the furnace and allowing the heating chamber to cool back to room temperature at an unforced rate with the chamber remaining closed).

in this case the annealed wafers were briefly dipped (for about 5 seconds) into a viscous hydrofluoric acid solution to etch the surfaces thereof. This rapid dip acid treatment step removes any silicon which may have diffused to the surface of the wafers without weakening the wafers by excessive etching at the grain boundaries. The resulting surface is found to be chemically clean as verified by a water break test.

With this latter sintered alloy the wafering procedure was the same as for the fusion cast material, but it was found that the wafers did not develop the severe degree of roughness after annealing experienced with the cast material, and consequently the reannealing step could be omitted. it is theorized that a sintering operation introduces less stress in the material than fusion casting, so that the annealing induces markediyless crystal shift.

The term ingot is used herein to refer to the product of a conventional fusion casting process and to the analogous product formed by compacting and sintering of powdered alloy material. The term denotes a product having the typical density of the fusion cast material or a product formed by sin tering but having comparable density. The term "ingot" as used herein requires an iron-silicon-aluminum alloy mass having a density comparable to that of fusion cast sendust such that the Rockwell hardness thereof is at least C40. The term ingot" requires a density of a sintered material of about sendust composition of at least 6.5 grams per cubic centimeter. Sintered materials of this density may have a direct current permeability (measured with A H equals 0.02 oersted on a ring sample with a thickness of 0.350 inch) of at least 6000, this permeability being defined as initial permeability herein.

I claim as my invention:

1. A composite magnetic transducer head comprising a ferrite magnetic core having magnetic pole tips defining a coupling gap for coupling of the core with a record medium, characterized in that at least one of the pole tips comprises laminations formed from an ingot of an iron-silicon-aluminum alloy, said laminations having a mechanical hardness of at least Rockwell C-40 and a thickness of about to 6 mils, said laminations having substantially smooth side surfaces, and a bonding layer between the successive laminations and mechanically bonding the laminations as a unitary structure, the successive bonding layers having a substantially uniform thickness dimension of about 200 microinches, said laminations having a density of about 7 grams per cubic centimeter and an initial penneability of at least about 6500.

2. A magnetic head comprising a magnetic core having magnetic pole tips defining a coupling gap for coupling of the core with a record medium, characterized in that the pole tips comprise laminations formed from fusion cast iron-silicon-aluminum alloy, said laminations having a hardness of at least Rockwell C-40 and a thickness of less than 8 mils, said laminations having lapped side surfaces which are substantially flat and smooth, and a bonding layer between successive laminations mechanically bonding the laminations as a unitary structure and having a thickness of less than 300 microinches, said laminations having an initial permeability of at least about 6500.

3. A magnetic head according to claim 2 with said laminations of said fusion cast alloy having been annealed, lapped smooth on the side surfaces thereof and then reannealed.

4. A composite multitrack magnetic transducer head assembly comprising a support bracket having a series of ferrite magnetic cores therein, the cores having respective pairs of edge faces all lying substantially in a common plane,

a pole tip assembly having secured thereto a series of pairs of pole tips with undersurfaces lying in closely spaced confronting relation to the respective edge faces to define respective head units for cooperation with respective channels of a magnetizable layer of a magnetic record medium.

said pole tips each comprising a series of laminations formed from an ingot of a sintered iron-silicon-aluminum alloy and having a hardness of at least about Rockwell C-40 and having a thickness of about 5 to 6 mils, said laminations having a density of at least 6.5 grams per cubic centimeter and an initial permeability of at least 6000.

5. A multitrack magnetic transducer head assembly according to claim 4 with said laminations having been etched with a viscous acid solution subsequent to annealing, and the laminations of each pole tip assembly having successive bonding layers therebetween mechanically bonding the laminations as a unitary structure and providing a substantially uniform spacing between the successive laminations of less than 300 microinches.

Claims

1. A composite magnetic transducer head comprising a ferrite magnetic core having magnetic pole tips defining a coupling gap for coupling of the core with a record medium, characterized in that at least one of the pole tips comprises laminations formed from an ingot of an iron-silicon-aluminum alloy, said laminations having a mechanical hardness of at least Rockwell C-40 and a thickness of about 5 to 6 mils, said laminations having substantially smooth side surfaces, and a bonding layer between the successive laminations and mechanically bonding the laminations as a unitary structure, the successive bonding layers having a substantially uniform thickness dimension of about 200 microinches, said laminations having a density of about 7 grams per cubic centimeter and an initial permeability of at least about 6500.

4. A composite multitrack magnetic transducer head assembly comprising a support bracket having a series of ferrite magnetic cores therein, the cores having respective pairs of edge faces all lying substantially in a common plane, a pole tip assembly having secured thereto a series of pairs of pole tips with undersurfaces lying in closely spaced confronting relation to the respective edge faces to define respective head units for cooperation with respective channels of a magnetizable layer of a magnetic record medium. said pole tips each comprising a series of laminations formed from an ingot of a sintered iron-silicon-aluminum alloy and having a hardness of at least about Rockwell C-40 and having a thickness of about 5 to 6 mils, said laminations having a density of at least 6.5 grams per cubic centimeter and an initial permeability of at least 6000.