Formation and Electromagnetic Properties of Large Single Crystals of Metal Hydrides

本研究的目的是（1）形成轮廓分明的大单晶金属氧化物和（2）研究这些金属氧化物的电和磁性能。本文研究了以LaNi_5，LaCo_5，GdFe_3，<23>Gd_6Fe_3，Mg_2Ni，NdCo_5，YCo_3，Y_6Fe_3<23>等稀土金属间化合物为基础的三元金属间化合物。劳厄X射线衍射表明它们是单晶，最大尺寸为8 mm d × 20 mm l。我们发展了一种原位测量非稳定态（高平衡氢压）电阻率的方法。结果表明，Mg_2Ni由金属转变为半导体，Mg_2NiH_3的能隙<3.1>为0.056eV; GdFe_3中吸氢后，晶格常数增加，补偿温度从280 K降低到161 K;在强磁场作用下，GdFe_3H_X的磁结构由简单亚铁磁结构转变为非共线磁结构。其临界场从24.7T下降到13.0T。从交换耦合常数的变化可以看出，交换作用的强度取决于氢的组成x。

The present study was concerned with (1) the formation of well-defined and large single crystals of metal hydrides and (2) the investigation of electric and magnetic properties for these metal hydrides. We investigated the ternary metal hydrids based on rare-eath intermetallics, such as LaNi_5, LaCo_5, GdFe_3, Gd_6Fe_<23>, Mg_2Ni, NdCo_5, YCo_3, Y_6Fe_<23>.The single crystals of the starting intermetallics were prepared by means of triarcmelting. Laue x-ray diffraction patterns showed that they were single crystals and the maximum size of them was 8mm d*20mm l.We developed an in situ method to measure the electrical resistivity unstable hydrides (with high equilibrium hydrogen pressures). It was observed that Mg_2Ni transits from a metal to a semiconductor as a result of hydrogenation and the energy gap of Mg_2NiH_<3.1> is 0.056eV.As hydrogen is absorbed in GdFe_3, the lattice constants is increased and the compensation temperature is decreased from 280K to 161K.Under the influence of high magnetic fields, the magnetic structure of GdFe_3H_X transits from a simple ferrimagnetic one to a non-colinear one. Its critical fields decreased from 24.7T to 13.0T.The strength of the exchange interaction depends on the hydrogen composition x judging from the variation in the exchange coupling constant.