Giant intrinsic magnetic hardness due to randomized crystal field interactions in SmNi5−xCux

Abstract

Giant intrinsic magnetic hardness is found at low temperatures in structurally homogeneous materials SmNi5−xCux. Magnetic hardness peaks at a composition SmNi2.5Cu2.5 where the crystal field disorder due to compositional randomization is at a maximum. By comparison with SmCo5−xNix, where giant intrinsic magnetic hardness originates, in part, from fluctuations from site to site of the magnitude of moment and strength of exchange of the transition metal, magnetic hardness in the SmNi5−xCux is predominantly due to anisotropy and concomitant exchange fluctuations on Sm sites.

Magnetic properties of RNi5−xCux intermetallics

“…A partial substitution of Cu for Ni increase H c sharply except for the case of GdNi 5Àx Cu x where H c was very low for all x. The SmNi 5Àx Cu x alloys have especially high H c values in accordance with results of [18] for polycrystalline specimens. In the case of R ¼ Sm and Tb, the maximum of H c (x) was observed at x ¼ 2.…”

“…All curves have a maximum at xE1. As we have outlined in Introduction, the maximum in the T C (x) curve was not observed for SmNi 5Àx Cu x in the paper [18]. It is possible that the T C values presented there, were influenced by an external magnetic field of 3 kOe which was applied in the course of T C measurements.…”

“…The appearance of high coercive force in the Cu substituted RNi 5Àx Cu x compounds can be explained also by the LUA effects, as was discussed earlier for the TbNi 5Àx Cu x [17] and SmNi 5Àx Cu x [18] alloys. Owing to the strong uniaxial magnetocrystalline anisotropy in combination with relatively week exchange interactions, domain walls are rather thin in the RNi 5 compounds.…”

“…We have found an unusual dependence T C (x) having a maximum at xE1 for RNi 5Àx Cu x alloys with R ¼ Pr, Gd, Tb [12,17]. Meanwhile, it was found that T C of the SmNi 5Àx Cu x alloys is almost constant up to x ¼ 1:4 and then it slowly decreases [18]. The compositional dependences of spontaneous magnetization M s (x) are rather different in the TbNi 5Àx Cu x [17] and SmNi 5Àx Cu x [18] systems.…”

“…Meanwhile, it was found that T C of the SmNi 5Àx Cu x alloys is almost constant up to x ¼ 1:4 and then it slowly decreases [18]. The compositional dependences of spontaneous magnetization M s (x) are rather different in the TbNi 5Àx Cu x [17] and SmNi 5Àx Cu x [18] systems. We have suggested in our previous works that the compositional behavior of magnetic properties in RNi 5Àx Cu x alloys can be explained by the effects of band magnetism and random local crystal fields (RLCF) which should take place for all R. To verify this idea, we have performed a systematic study of magnetic properties of RNi 5Àx Cu x for R ¼ La, Ce, Nd, Sm, Dy, Ho, Er, Tm, Lu.…”