Magnetic properties of the premartensitic transition in Ni 2 MnGa alloys
Magnetic properties of the premartensitic transition in Ni 2 MnGa alloys
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DOI：
10.1103/physrevb.58.11127
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发表时间：
1998-11
影响因子：
3.7
通讯作者：
F. Zuo;X. Su;K. Wu
中科院分区：
文献类型：
--
作者：
F. Zuo;X. Su;K. Wu
本文报道了铁磁Heusler合金Ni_2MnGa的磁化强度随磁场和温度的变化。在马氏体相变点以上的磁化强度表现出与磁场相关的峰值效应，这是预马氏体相存在的直接磁性证据。在低场下，峰值效应发生在与从中子散射，电子显微镜和超声研究中观察到的这种化合物的微调制结构转变相一致的温度下。在高场，峰值效应被抑制。峰值温度的强场依赖性表明在中间相存在大的磁弹性相互作用。@S0163-1829~98！09537-X#在20世纪80年代早期首次研究了具有x 50的铁磁Heusler合金Ni 22 xMn 11 xGa。1对于化学计量比的Ni_2MnGa合金，发现该合金是铁磁性的，居里温度为376 K。从显微镜和中子散射测量观察到的马氏体相变从立方结构到复杂的四元结构在202 K冷却，在相同的温度下，在磁化强度相应的跳跃。后来对非化学计量成分合金的研究表明，居里温度和马氏体转变都可以随x而变化。2 - 4最近对Ni 22 xMn 11 xGa合金作为形状记忆材料的兴趣导致了对结构转变的更仔细的研究。据报道，马氏体相变是通过从几个实验，如X射线，电子和中子散射，和超声测量观察到的预马氏体相变。[5 - 11]然而，人们普遍认为没有对应于预马氏体相变的磁异常。2 - 4在本文中，我们报道了化学计量比Ni 2 MnGa合金的预马氏体相变的直接磁性表征。磁化强度M作为温度T的函数，在不同的外加磁场H显示出明显的预马氏体转变的证据。预马氏体转变的特征在于M（T）的峰值远高于马氏体转变温度Tm。发现预马氏体转变温度Tp依赖于外加磁场。场的依赖性的T p表现出大的磁弹性效应在premartensitic或中间状态。样品是用传统的电弧熔化工艺制备的，具有起始材料的化学计量组成。1结构分析证实单相，
Magnetization as a function of field and temperature for a ferromagnetic Heusler alloy Ni2MnGa is reported. Magnetization above the Martensitic transition displays a field-dependent peak effect, a direct magnetic evidence of premartensitic phase. At low fields, the peak effect occurs at a temperature consistent with the observations of the micromodulated structure transition seen from neutron scattering, electron microscopy, and ultrasonic studies in this compound. At high fields, the peak effect is suppressed. The strong field dependence of the peak temperature suggests a large magnetoelastic interaction in the intermediate phase. @S0163-1829~98!09537-X# The ferromagnetic Heusler alloy Ni22xMn11xGa with x 50 was first studied in the early 1980’s. 1 For the stoichiometric Ni2MnGa, the alloy was found to be ferromagnetic with a Curie temperature of 376 K. A martensitic phase transition from a cubic structure to a complex tetragonal structure at 202 K on cooling was observed from microscopy and neutron-scattering measurements, with a corresponding jump in magnetization at the same temperature. Later studies on alloys with nonstoichiometric compositions show that both the Curie temperature and the Martensitic transition can be varied with x. 2‐4 Recent interest in the Ni22xMn11xGa alloys as shape memory materials has lead to much more careful studies of the structural transition. It has been reported that the Martensitic transition is proceeded by a premartensitic transition as observed from several experiments such as x-ray, electron- and neutron-scattering, and ultrasound measurements. 5‐11 However, it is generally believed that there is no magnetic anomaly corresponding to the premartensitic transition. 2‐4 In this paper, we report direct magnetic characterizations of the premartensitic transition for the stoichiometric Ni2MnGa alloy. Magnetization M as a function of temperature T at various applied field H shows clear evidence of a premartensitic transition. The premartensitic transition is characterized by a peak in M(T) well above the Martensitic transition temperature Tm . The premartensitic transition temperature T p is found dependent on the applied field. The field dependence of T p demonstrates a large magnetoelastic effect in the premartensitic or intermediate state. Samples are prepared with the conventional arc-melt process with the stoichiometric composition of starting materials. 1 Structural analysis confirms the single phase,