Magnetic anomalies and structures in Ni/Mn multilayers

Abstract

Ni/Mn multilayers were prepared by the vapor deposition method. The appearance of high spin states in the Mn layers at a low temperature was synthetically clarified from the magnetizations, the exchange biased fields, the spin flopping transition, and the resistivity. Some structural factors that affect the appearance of high spin states were determined. The exchange biased fields showed that high-spin-state Mn layers are antiferromagnetic. The low spin flopping transition fields revealed that the exchange interaction and magnetic anisotropy of the Mn layers were largely reduced, resulting in large magnetizations of high-spin-state antiferromagnetic Mn layers. From a large magnetization, 139 emu/g, of the Ni(20)/Mn(4) in 5 T at 5 K, the largest magnetization, 497 emu/g, of the Mn layers was estimated to be in a high spin state. The Néel temperature (8.2 K) was estimated from saturation magnetization (500 emu/g) and susceptibility (43.1) of the Mn layers. On the other hand, from the temperature dependencies of the exchange biased fields, the Néel temperature was estimated to be 5–20 K. The increase in electric resistance accompanying a decrease in temperature indicated that the transition from a low spin state to a high spin state was accompanied by a localization of 3d-electrons. These magnetic anomalies were qualitatively discussed from the interplanar spacings, the textures, the interfacial roughnesses, Mn layer thicknesses, and relative thicknesses of Ni layers to those of Mn layers.