Abstract
Spin valve magnetic sensors have been demonstrated as the most promising candidates for high-area-density magnetic read heads. Since the antiferromagnetic biasing layer is one of the key elements of the spin valve, the anisotropy exchange between antiferromagnetic and ferromagnetic layers has received much theoretical and experimental attention; however, a complete understanding of the controlling paremeters for anisotropic exchange remains elusive. Exchange anisotropy of NiFe/FeMn and NiFe/NiMn has been extensively studied for the pinning structures of spin valves. The uni-directional anisotropy due to the coupling in those systems was induced either by depositing NiFe in the magnetic field or by annealing the samples in the magnetic field. In this work, epitaxial (111)NiFe and NiFeMn were prepared by a molecular beam epitaxy(MBE) system on the Al2O3/Mo structural templates. During the deposition of samples, no magnetic field was applied. During the depositions, reflection high energy electron diffraction (RHEED) was in-situ taken to monitor the surface structure and the epitaxial orientation relationship between layers. After depositions, the crystalline structures were characterized by x-ray diffraction (XRD), and the hysterisis loops were measured by VSM and magnto-optical Kerr effect (MOKE) at room temperature. Since the lattice mismatch between NiFe and Mo, this stress may induce a strong uniaxial anisotropy in NiFe. Consequently, the spins in NiFe mainly align in this axis (either in positive or negative direction). This strong uniaxial anisotropy behaves like an internal field, which affects the spin orientations of NiFeMn at the interface. Because of the epitaxial growth between NiFe and NiFeMn, the exchange coupling can be strong enough to form muti-domains in NiFeMn to reduce the interfacial energy between NiFe and NiFeMn. As a result, for MOKE experiments, when the laser spots covered two domains, dual shifted loops were observed. We have successfully prepared a stress-induced exchange biasing system[NiFe(8nm)/NiFeMn(12nm)] with exchange field of 135 Oe, and the coercivity of 87 Oe.