In Ni-Mn-X（X=In,Sn,Sb） ferromagnetic shape memory alloys,a ferromagnetic transition from paramagnetic to ferromagnetic austenite and a martensitic transformation from ferromagnetic austenite to weak magnetic martensite occur in some particular composition ranges,in which abundant physical properties have been observed by the abrupt change of magnetization and resistivity around their transition temperatures in these alloys.Therefore,tuning the martensitic transformation temperature（TM） and enlarging the workingtemperature interval for Ni-Mn-X（X=In,Sn,Sb） alloys,are of great importance.In the present paper,we will focus on the effect of external factors,including pre-deformation,annealing,and high pressure annealing,on the magnetic transitions and the related magnetocaloric properties in Ni-Mn-Co-Sn ferromagnetic shape memory alloys.Our approaches and the main results in this particular field will be reviewed.
The stability and local vibrational mode（LVM） of hydrogen related p-type AlN have been studied by firstprinciples calculations based on density functional theory.The stable and metastable microscopic geometries of group-Ⅱ（Be,Mg,Ca,Sr,Ba）-H complexes have been investigated.The calculated results indicate that BC_（‖） is the most stable configuration for isolated interstitial H~＋ and Be-H complexes,while it is AB_（n,⊥） for Mg-H,Ca-H,Sr-H and Ba-H complexes.Moreover,the vibrational frequencies and the values of k and ｜α｜ for the H atom with LVM are calculated. Here,the values of k and ｜α｜ are used to describe the parameters of the harmonic and anharmonic contributions,respectively. The calculated results indicate that the larger the size of the doped ion is,the shorter the N-H bond length is,and the larger the potential energy,the vibrational frequencies,the values of k and ｜α｜ are.This implies that the size of the doped ion has an important influence on the vibrational properties of H.
Based on Monte Carlo method, the hysteresis loops for both individual Co nanowires and their array were simulated, and the influence of the strength of the dipolar interaction on the macroscopical magnetic properties of Co nanowire array was investigated. The simulated results indicate that the coercivity approximately increases linearly with the increase of the strength coefficient of the dipolar interaction. The interwire dipole interaction between wires tends to develop a magnetic easy axis perpendicular to the wire axis. In the magnetic reversal process, competition between the interwire dipolar interaction and the shape anisotropy of individual wires which forces the moments to orient along the axis makes the magnetic reversal of the array different from that of individual wire. For applied field parallel to wire axis, the coercivity of nanowire array increases rapidly with the increase of the nearest-neighbor interwire distance, and approximately increases linearly with the increase of the strength coefficient of the dipolar interaction for the fixed diameter and the nearest-neighbor interwire distance. While for applied field perpendicular to wire axis, in contrast, the coercivity decreases with increasing the nearest-neighbor interwire distance, and nearly remains a constant with the increase of the strength coefficient of the dipolar interaction.
Zn0.93Co0.07O thin films infiltrated with nitrogen and aluminum were prepared by means of magneton sputtering. The structural and magnetic properties of the films were studied systematically. The materials were single phase (wurtzite structure) with surfaces showing signs of homogeneous growth. The films were ferromagnetic at room temperature, and magnetic domains could be clearly observed on the surfaces. In the case of Al infiltration, saturated magnetization increased with Al concentration increasing; whereas in the case of N infiltration, saturated magnetization decreased with the increase in N concentration. The results show that ferromagnetic interactions in Co-doped ZnO diluted magnetic semiconductor may be transferred by electrons.
