Proceedings of the Fifth Vietnamese-German Seminar on Physics and Engineering, Hue, 25 February - 02 March, 2002 Preparation and some characteristics of NiMn antiferromagnetic thin films used for low-field spin valves Nguyen Anh Tuan a , Nguyen Hoang Luong b , Nguyen Chau b , Vuong Van Hiep b , Nguyen Duc Linh b , Nguyen Thi Minh Ha b a International Training Institute for Materials Science (ITIMS), Hanoi, Vietnam, E-mail: tuanna@itims.edu.vn. b Center for Materials Science (CMS), University of Science, Vietnam National University, Hanoi, Vietnam, E-mail: luongnh@vnu.edu.vn; chau@cms.edu.vn NiMn alloys are antiferromagnetic up to rather high temperature, T N ~ 380 o C, and are strongly interested at the present time. These alloys are used for pinning magnetization in the spin valves operated at low magnetic field regions. In this paper, we study preparation of NiMn thin films by rf sputtering, investigate some characteristics in technology as well as in structure of them. The exchange-biased coupling (EBC) between the NiMn film and a Co ferromagnetic film, is also examined. Investigations on the magnetic properties showed rather complex features in this system. 1. Introduction In 1991, Dieny et al had firstly shown a type of pinning spin valve, in which a FeMn antiferromagnetic (AF) layer used for pinning magnetization of an adjacent ferromagnetic (FM) layer [1]. Since then, capacity for application of giant magnetoresistance (GMR) effect at low field in the heads of modern computers or in some other magnetoelectronics devices had been opened. The pinning was based on exchange anisotropy phenomenon, or exchange bias (EB), created between atomic layers at interface of AF and FM layers. This is the phenomenon discovered by Meiklejohn and Bean in 1956 [2], but it was almost not concerned after that. FeMn is an antiferromagnet and is known to be very sensitive to corrosion [3]. Attempts were made to find other antiferromagnets for replacing it. Antiferromagnets used as a pinning layer in spin valves include demands such as high blocking temperature, large pinning field, intensively exchange coupling strength, high thermal stability and good corrosion resistance. Recently, some of alloys of Mn or oxides of ferromagnetic metals, for example alloys such as NiMn [4], InMn [5], PdPtMn [6], PtMn [7] and PdMn [8], or several oxides such as NiO [9, 10], Fe 2 O 3 [11] and NiCoO [12] have been used in the spin valves. In general, above antiferromagnets have pinning field (H p ) rather large, H p > 300 Oe, and rather high blocking temperature, about from 400°C up. However, from point of view of simple technology, easy for preparation and low cost, but still guarantee the above demands for antiferromagnets used in spin valves, we think that NiMn alloy is very suitable. NiMn antiferromagnetic alloy has T N ~ 380°C, H p ~ 650 Oe and very good corrosion resistance [4]. In the other hand, the knowledge on the technology, some characteristics and properties of NiMn thin films is still yet rather poor. In this paper, we report some results studying on preparation and magnetic properties of NiMn thin films. These results will be used in further research on the application of low- field spin valve elements in read-heads. 141