Magnetic ordering in MnB2: an ab initio study

We present an ab initio study of different possible magnetic states of the hexagonal intermetallic compound MnB2 employing the augmented spherical wave method. The calculations show that the ground state of MnB2 is antiferromagnetically ordered. The calculated magnetic moment of Mn is close to 2 mu(B) for both the antiferromagnetic (AF) and the ferromagnetic (FM) states. This result is in contradiction to the earlier experiments which classified MnB2 as an itinerant ferromagnet. This experimental conclusion was drawn from magnetization and susceptibility measurements which find a small saturated moment (similar to 0.2 mu(B)/Mn) and a high Rhodes-Wohlfarth ratio. Our calculation shows that the density of states exhibits a d-band splitting of the Mn subband of about 2 eV and that the spin-up d-subband is placed well below (similar to 1 eV) the Fermi energy implying a certain degree of localization of manganese d-states. It appears that the calculated effective moment is in good agreement with the value obtained experimentally from the Curie-Weiss fit to the paramagnetic susceptibility. In order to resolve this contradiction we suggest a spin canting structure which could be responsible for the small FM component found in the experiment. (C) 2000 Elsevier Science Ltd. All rights reserved.