Magnetic Properties of Mn_3-xNi_xB₄and Mn_3-xCo_xB₄

Abstract

Thermomagnetic properties of Mn 3- x Me x B 4 (Me=Ni or Co; 0.36≧ x >0) were investigated in the temperature range from -196°C to 300°C. The antiferromagnetic characteristics of these compounds are almost similar to those of the parent compound Mn 3 B 4 at high temperatures, and a monotonic decrease of the Néel point is observed depending on the amount of Ni or Co present. With decreasing temperature, however, the susceptibility undergoes a transition to ferromagnetic state, and exchange inversions are observed at temperatures between -140°C and -10°C depending on the value of x in the formula. Magnetizations of these compounds are unsaturable even under the field of 18,000 Oe and are as large as 30∼40 e.m.u./g. From the results of the present experiment, the spin assignment in Mn 3 B 4 is discussed again. It is concluded that manganese atoms on 4(g) exclusively can contribute to the magnetism.