Study of magnetism in Fe-Ni Invar alloys by mechanically alloying

镍含量约为35原子%的铁镍合金被称为因瓦合金，因瓦合金以其非常小的热膨胀系数而众所周知。除了这些热膨胀异常外，因瓦合金还表现出各种磁性能异常，如Slater极化曲线上磁矩的异常降低，居里温度的异常大的压力效应等，这些异常起源于具有fcc晶格结构的3d带电子，因此，因瓦合金的磁性对于金属和合金的磁性研究特别重要。指出Fe-Ni因瓦合金总是存在一定的浓度波动，这对其磁性能有一定的贡献。然而，很少有人通过人为改变浓度波动来进行磁性研究。采用机械合金化和高温连续退火的方法， ...更多信息 d，使得浓度波动比通过常规熔融合金化获得的浓度波动宽得多。测量了机械合金化Fe-Ni因瓦合金的居里温度、磁化率和磁化曲线。结果表明，居里温度随浓度波动幅度的增大先降低，达到最小值，然后又大幅度升高。饱和磁化强度随涨落宽度的增大先减小后增大，达到最小值。高场磁化率随涨落宽度的增大先减小，出现极大值后减小。这些性质可以通过考虑浓度波动的高斯分布来解释。利用加速器对Fe-Ni因瓦合金进行了高能重离子辐照。结果表明，辐照后样品的居里温度明显升高，剂量为10 μ cm-3时，居里温度可达100 K<14><-2>。这种效应为纳米级磁存储器件的应用提供了可能。少

Fe-Ni alloys with the Ni-concentration around 35 at.% are called the Invar alloys, which are well known with their very small thermal expansion coefficients. Besides those thermal expansion anomalies, Invar alloys show various anomalies in magnetic properties such as abnormal decrease of the magnetic moment from the Slater-Poling curve, anomalously large pressure effect of the Curie temperature and so on. Those anomalies are originated in the 3d-band electrons with a fcc-lattice structure, and therefore, the magnetic properties of Invar alloys are especially important for studies of magnetism in metals and alloys. It was pointed out that Fe-Ni Invar alloys always have a certain amount of concentration fluctuation, which makes some contribution to their magnetic properties. However, there have been made very few magnetic studies by artificially changing the concentration fluctuation. By adopting a method of mechanically alloying and successive annealing at high temperatures, we succeede … More d to make the concentration fluctuation much wider than those obtained by conventional alloying by melting. Measurements of the Curie temperature, magnetic susceptibility and magnetization curves were made on those mechanically alloyed Fe-Ni Invar alloys. It was found that the Curie temperature decreased first with increasing the range of the concentration fluctuation, taking a minimum, and then, increased largely. The saturation magnetization also decreased first, taking a minimum, and then increased with increasing the fluctuation width. The high-field susceptibility decreased first with increasing the fluctuation width, taking a maximum, then, decreased. Those properties could be explained by considering a gaussian distribution for the concentration fluctuation. By using an accererator, high-energy heavy ion irradiation were made on Fe-Ni Invar alloys. It was found that the Curie temperature of the irradiated part increased largely, as large as 100 K with the dose of 10^<14> cm^<-2>. This effect has a possibility for application of nano-scale magnetic memory device. Less