Giant magnetoresistance of magnetic granular phase of FeRh ordered alloy

由于铁磁-反铁磁相变是一阶相变，因此由相变引起的电阻率的大变化被认为是难以利用的。然而，很明显，在从高温铁磁相到低温反铁磁相的相变的中间期间由施加磁场引起的电阻率的变化具有小的且可逆的磁滞。为了弄清这种电阻率大变化的机理，对样品进行了冷轧和各种热处理。讨论了电阻率的变化与相变和磁性微结构的关系。实验认为，在磁性相变过程中出现的磁性结构是铁磁相和反铁磁相的混合物，类似于冷却的颗粒态，部分磁阻是由磁性晶界处的传导电子的自旋无关衍射引起的。这些研究结果发表在日本磁学学会杂志上。然后，我们尝试用MFM观测磁性颗粒态，得到了支持我们设想的结果，作为应用尝试，我们尝试用弱磁场获得大的磁电阻变化。将0.5mm长、2 mm宽、1 mm厚的Fe-Rh样品夹在两块5 mm长、2 mm宽的铁板之间。然后通过从点焊机引入一个脉冲电流将样品与铁板连接。这种异质结构样品表现出5.4%的相对磁电阻变化6.6kOe。该变化比没有铁板的样品获得的变化大5倍。Rh组分的磁阻变化的依赖性进行了研究。具有51at%Rh的样品显示出最大的磁电阻的磁场依赖性。

Since the ferromagnetic-antiferromagnetic phase transition is first ordere transition, the large change in resistivity caused by the transition is considered to be difficult to use. Howecer, it became clear that the change in resistivity caused by an application of magnetic field during the midway of the phase transition from high temperature ferromagnetic phase to low temperature antiferromagnetic phase has a small and reversible hysteresis. Therefore, the application of this change in resistivity is possible.In ordere to make clear the mechanism of this large change in resistivity, samples were cold rolled and performed various kind of heat treatments. Then, the change in resistivity was discussed in relation to the phase transition and magnetic microstructure. From this experiment, it is considered that the magnetic structure which appears on the midway of magnetic phase transition is the mixture of ferromagnetic and antiferromagnetic phases mixed like the so colled granular state, and a part of magnetoresistance is due to the spindependent diffractions of conduction electrons which occur at the magnetic grain boundary. These results were presented to the journal of the magnetics society of japan. Then, we tried to observe the magnetic granular state by MFM,and obtained results which suport our consideration.As an applicational attempt, we tried to get large change in magnetoresistance by weak magnetic field. A Fe-Rh sample 0.5mm long 2mm wide 1mm thick was sandwiched between two iron plates 5mm long and 2mm wide. Then sample was connected with the iron plates by introducing one pulse of current from a spot welder. This heterostructural sample showed large relative magnetoresistance change of 5.4% by 6.6kOe. This change is 5 times larger than that obtained for a sample without iron plates. Rh conposition dependence of the change in magnetoresistance was examined. The sample with 51 at% Rh showed the largest magnetic field dependence of magnetoresistance.