Magnetic and electronic structures of MSM alloys Ni1-x-yMnxGay

Abstract

Non-stoichiometric alloys Ni 1-x-y Mn x Ga y characterised by different values of magnetic shape memory effect (MSME) from 0.2 to 7.3% were studied using ferromagnetic resonance (FMR). The angular dependence of FMR signals was measured in the martensitic and austenitic states of the samples just before and after martensite-to-austenite transition. Experimental data were used for determination of the magnetisation 4πM s and anisotropy parameters K 1 , K 2 for the martensitic state and Kc for the austenitic state. A special feature of the alloys possessing high MSME is a larger value of the coefficient K 2 . The temperature dependence of the FMR signals was investigated in the range from temperatures below M s to those higher than T C where FMR is transformed into the conduction electron spin resonance (CESR). The main difference between the alloys in the martensitic state revealing the large or small MSM is the behaviour of the electron system. In the alloys with the small MSME all the electrons are included into the ferromagnetic system. On the contrary, in the alloy with the large MSME the narrow resonance line of one electron subsystem is separately present in the FMR spectra. An intensive signal of CESR is observed in the alloys with the large MSME, which is an evidence for a high concentration of free electrons. The suggestion is made that the high concentration of free electrons, i.e. enhanced metallic character of interatomic bonds, assists MSME.