Recent Progress on Rare Earth Magnetic Regenerator Materials

Our group has reported several candidates for magnetic regenerator materials in the helium temperature range, such as, Er(Ni1-xCox)2 Er(Ni1-xCox)2, ErNi and Er3Ni. However, those Curie temperatures Tc’s are more than ~5.5 K and the specific heats C(T)’s of those systems become very small near 4.2 K. In the present investigation we have succeeded in developing a new low Tc material, Er0. 9Yb0. 1Ni2 whose Tc is ~4 K. Moreover, other new regenerator materials, such as Er1-xYbxNi and Er1-xHoxNi2 have also been investigated and usefulness of those compounds was verified. We have also studied the origin of the small C(T) of some Er compounds near 4.2 K and it has been made clear that the Schottky type specific heat reduces the absolute value of C(T) in low temperature range.