Magnetic Head With Mechanically Isolated Thin Film Sensor

1. Field of the Invention

This invention relates in general to magnetic heads, and in particular to a magnetic head -- and to a method for making such a head -- in which the windowed back section of the head is bridged by a single domain thin magnetic film coated wire having a sense coil wound thereabout.

2. Description of the Prior Art

In practicing the teachings of McClure (U.S. Ser. No. 835,110) and Moeller (U.S. Ser. No. 835,105), commonly assigned, it happens that anomalies may appear in the characteristic curves of some, but not all, of the magnetic heads according to those teachings. For example, at a certain current through the sense coil of a head according to the teaching of Moeller . . . the current serving to apply a bias field along the hard axis of the film . . . a "switching" transient appeared in the output of the sense coil. As will appear below, the invention postulates a theory to explain such behavior and provides apparatus/method, in correspondence with such theory, to preclude such behavior.

It turns out that thin film wire sensors are supplied by their suppliers in throw-away glass shipping tubes, such tubes serving to protect the fragile thin (about 3 microns or less) magnetic films from handling damage. Such glass shipping tubes are, in one aspect of the invention, modified and reused to implement the theory which is at the root of the invention.

On the basis that anomalies in performance characteristics of a head of the type under discussion are caused by mechanical strains in the single domain magnetic film thereof, i.e. the film dipoles are switchable by stressing the film, the invention precludes the tight winding of the sense coil directly on the magnetically coated wire. To this end, the sense coil is wound on a hollow mandril, and then the coated wire is threaded through the hollow of the mandril, the mandril being shorter than the coated wire. Next, the coated wire, with the coil supporting mandril thereon, is bonded in place to the head back part, thereby effectively completing construction of the head.

Since the above-noted glass shipping tubes are designed as sense wire "protective housings", they serve as ideal mandrils for respective coils. Accordingly, in practicing the invention the glass shipping tubes are cut to respective "mandril-lengths", each mandril-length being provided with a sense coil. Bonding the wire-mandril-coil combinations to respective head front parts takes place as noted above.

The invention will now be described with reference to the FIGURE, which is a perspective view of apparatus according to the invention:

A pair of ferrite pole pieces 10, 12 cooperate to define a transducer gap 14 for a head 8; and a non-magnetic back bar 16 cooperates with the pole pieces for purposes of support. The pole pieces 10, 12 are notched at 18, 18', respectively, and a single domain thin magnetic film coated wire 19 is bonded to the pole pieces in such notches. A non-magnetic tube 20, e.g. one made of glass, having an axial opening 22 sufficient to avoid stressing the film on the wire 19 has the wire 19 threaded through it; and a sense coil wraps around the tube 20 which serves as the mandril for the coil 24. Although the mandril 20 effectively causes an increase in the impedance of the coil 24, the advantages of "performance predictability", resulting from mandril-assured non-stressing of the thin film far outweigh such impedance increase.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.