NIO STRUCTURE-EXCHANGE ANISOTROPY RELATION IN THE NI81FE19 NIO FILMS AND THERMAL-STABILITY OF ITS NIO FILM/

We studied an antiferromagnetic (AF) NiO film for an exchange-biased l ayer, focusing especially on the relationships between the exchange co upling properties of the Ni81Fe19(top)/NiO(bottom) films and the chara cter of its NiO film. Among the variable sputtering conditions, our ex perimental data showed that the dominant factor determining the exchan ge coupling properties was the Ar pressure during the NiO film prepara tion. Better exchange coupling properties resulted when the NiO film w as deposited at low Ar pressure which was attributed to: (i) the smoot h surface of the NiO film and (ii) the presence of relatively large pa rticle sizes within it. The former was thought to bring about not only an increase in the number of unidirectional exchange coupled Ni81Fe19 /NiO spins, but also the appearance of exchange paths having large loc al exchange anisotropies. The latter was thought to produce an increas e in the AF clusters with a particle volume larger than K(ei)A/K-AFi, where K-ei, A, and K-AFi are local unidirectional anisotropy, interfac ial area of the NiO cluster in contact with the Ni81Fe19 film, and loc al magnetocrystalline anisotropy of the NiO cluster, respectively. Mor eover, the NiO film was thermally stable up to 250 degrees C, although the AF anisotropy of the NiO film was weakened on increasing the anne aling temperature above 250 degrees C. (C) 1996 American Institute of Physics.