Kind Of Magnetic Material Research Articles

高エントロピー磁性材料を用いたＧＭ冷凍機の高性能化の研究

In the present paper we have investigated the method to produce the high efficient regenerator by using the magnetic regenerator materials in the He temperature range. These days, the magnetic materials with low magnetic phase transition temperature Tc are thought to be the promising regenerator materials below 10K. However, the very sharp peak of the magnetic specific heat CJ appears near Tc in the temperature dependence curve and, moreover, its value is almost same order of the value of the specific heat of the He gas. Therefore, it is difficult to make the efficient regenerator by using only a kind of a magnetic material. In the present investigation, in order to produce the highly efficient regenerator, we selected two kinds of magnetic materials whose Tc's are different, and produced the layered type regenerator in which the magnetic material with the high Tc piled up that with the low Tc. In the computer simulation and experiment it is verified that the layered type regenerator (Er0.9Yb0.1Ni+Er3Ni) is more efficient than that with only Er3Ni. Moreover, we have made new double-layered regenerator with Er0.9Yb0.1Ni and Er3Co, where Tc of Er3Co is almost twice Tc of Er3Ni. Applying this regenerator to the GM refrigerator, we have succeeded to obtain the fairly large refrigeration capacity of 1.05W at 4.2K. Finally, on the basis of the above results, we discussed the direction of the development of the magnetic regenerator in future.

Magnetovolume effects in Laves phase intermetallic compounds

First, general aspects of magnetovolume effects in various kinds of magnetic materials are summarized. Then the magnetovolume effects in rare earth-transition metal intermetallic compounds RM 2 are reviewed. RCo 2 show large magnetovolume effects which are attributable to an induced Co moment. We have recently observed a large spontaneous volume magnetostriction in the RMn 2 series. Among them YMn 2, which has been found to be an antiferromagnet, shows the largest volume magnetostriction of about 5%. On the other hand, it has been reported that some Np cubic Laves phase intermetallic compounds also show large pressure effects. These large magnetovolume effects can be interpreted generally in terms of itinerant electron ferromagnetism taking into account spin fluctuations, i.e. a local band theory of itinerant ferro- or antiferromagnetism.