THERMAL-STABILITY OF THE (100) CU-NI SUPERLATTICES WITH REVERSED MAGNETIC-ANISOTROPY

The (100) Cu(100 angstrom)-Ni(25 angstrom) superlattice structure, grown on Cu/Si(100), that shows a reversed magnetic anisotropy between the in-plane and normal-to-plane magnetizations, has been heated to 400-degrees-C, and the magnetic and structural changes investigated. The periodic structure remains mostly intact up to a 30-min heating at 300-degrees-C, and partially so after heating at 400-degrees-C. The reversed anisotropy, with a hysteresis loop seen for the field perpendicular to the film plane, but not for that parallel to the film plane, remains seen up to 400-degrees-C. This is compared with two (100) Cu/Ni/Cu structures containing 50- and 500-angstrom Ni, respectively, with two 1000-angstrom Cu layers each. The former structure, with a completely reversed magnetic anisotropy, lost both the Ni layer and the magnetic characteristics after heating at 200-degrees-C. The latter structure retained its magnetic properties up to 300-degrees-C, and lost both the Ni layer and the magnetic characteristics after heating at 400-degrees-C. The different reactions involved are discussed, including that with Si and mixing between Cu and Ni.