The influences on magnetic properties of substitution of Cu for Ni in NiMnSb alloys

摘要

We have investigated the effects on magnetic properties of NiMnSb alloys with substitution of Cu for Ni. The half-Heusler type alloys Cu_xNi_(1-x)MnS have been fabricated by the arc melting method and subsequently annealed at 1050 K for 24 h. All the samples retain the half-Heusler type structure. Lattice constants increase slightly with increasing Cu composition. It was found that at 300 K and in a field of 10 kOe for Cu_xNi_(1-x) MnSb samples the magnetization almost remains unchanged for x < 0.4. With increasing x above 0.4, the magnetization starts to decrease. When x is above 0.8 the magnetization decreases to near zero. At 100 K, the range in which the magnetization does not change expands to x < 0.7. A significant magnetization was found with a further increase of x; it approaches zero when x is over 0.9. The Curie temperature decreases with increasing Cu content. The curve of Curie temperature versus Cu composition can be fitted with formula of T_c = A - Bx~2, which reflects the weakening in exchange energy with substitution of Cu for Ni in NiMnSb alloys. For x < 0.4, little change was found for the magnetostriction. For 0.4 < x < 0.8, the magnetostriction decreases drastically with increasing Cu composition and decreases near to zero at x = 0.8, which is consistent with the dependence of magnetization versus Cu composition.