EFFECT OF AL SUBSTITUTION ON THE MAGNETIC-PROPERTIES OF RCO5 (R = RARE-EARTH)

Magnetic and structural characteristics of RCo5-xAlx have been established for R=Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, and Tm. All systems have the CaCu5 structure. Al and Co are randomly distributed over the Co-sublattice sites. Al-substitution decreases μCo and Tc and significantly alters magnetic anisotropy. Analysis of the magnetic anisotropy data shows that the Sm anisotropy in SmCo4Al is only 32% of that in SmCo5. In terms of the point charge model this requires that Al carry a positive charge. This is consistent with inferences drawn from the decreased Co moment accompanying Al substitution, which implies electron transfer from Al to Co. At room temperature, RCo4Al systems are uniaxial for R=Y, La, Ce, Pr, Sm, and Er, whereas for R=Nd and Dy the magnetization is at an angle with respect to the unique c axis. PrCo 4Al, NdCo4Al, DyCo4Al, and TmCo4Al exhibit changes in anisotropy at about 165, 295, 420, and 84 K, respectively.