FILM SM-CO PERMANENT-MAGNETS FOR THE BIASING OF THIN PERMALLOY STRIPS

Highly textured Sm-Co-based permanent magnet films which exhibit in-plane anisotropy, with thicknesses ranging from 500 angstrom to several microns, have been synthesized on polycrystalline Al2O3 substrates. The textured Sm-Co-based films of the disordered TbCu7-type structure were directly crystallized by sputter deposition onto heated substrates. Remanent inductions B(R) were almost-equal-to 8 kG, and the intrinsic coercivities, (i)H(c), ranged from 4-10 kOe. The crystallite grain size as a function of film thickness was determined. The use of these films in small scale geometry devices was tested in a sandwich configuration of strips of areal size 7 X 1 mm2. The Sm-Co films were used to bias Ni81.5Fe18.5 permalloy films. The sandwich permanent magnet was magnetized across its width. The permalloy films were sputter synthesized under conditions very similar to those of the permanent magnet films. Substrate biasing was not used for either the permanent magnet or the permalloy strips. The permalloy films exhibited a well-defined easy axis along the length of the strip. Unbiased, the permalloy showed a maximum magnetoresistance MR(max) of 3.0%. On biasing with a 25-mum-thick permanent magnet film with a spacer thickness of 25 mum, the longitudinal biasing field value at MR/MR(max) = 0.5 was more than a 100 Oe, indicating an average biasing field of the same value.