Giant magnetoresistance of magnetic granular phase of FeRh ordered alloy

由于铁磁-反铁磁相变是一阶相变，因此这种相变引起的电阻率大变化被认为是难以使用的。然而，在高温铁磁相向低温反铁磁相转变的过程中，由于施加磁场而引起的电阻率变化具有很小的可逆滞后。因此，这种电阻率变化的应用是可能的。为了弄清这种电阻率大变化的机理，对试样进行了冷轧和各种热处理。然后，讨论了电阻率的变化与相变和磁微观结构的关系。本实验认为，在磁相变的中间出现的磁性结构是铁磁相和反铁磁相的混合物，类似于颗粒态的混合，磁电阻的一部分是由于导电电子在磁晶界处的独立衍射造成的。这些结果发表在日本磁学学会杂志上。然后，我们尝试用MFM观察磁性颗粒状态，得到了支持我们考虑的结果。作为一种应用尝试，我们试图通过弱磁场获得大的磁电阻变化。将长0.5mm、宽2mm、厚1mm的Fe-Rh样品夹在长2mm、宽2mm的两块铁板之间。然后通过点焊机的一脉冲电流将试样与铁板连接起来。该异质结构样品的相对磁阻变化较大，为5.4%，变化幅度为6.6kOe。这种变化比没有铁板的样品大5倍。研究了Rh成分对磁阻变化的依赖性。Rh为51的样品对磁电阻的磁场依赖性最大。

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.