Magnetic and thermal properties of alloys close in composition to the spin gapless semiconductor Mn₂CoAl

The field dependence of magnetization at T = 4.2 K and in magnetic fields of up to 70 kOe, temperature dependences of magnetization (2 K < T < 300 K), heat capacity (2 K < T < 30 K) and magnetic susceptibility (2 K < T < 1000 K) for Mn_1.99Co_0.96Al_1.05 and Mn_1.79Co_1.25Al_0.96 alloys, closed in composition to the Mn₂CoAl spin gapless semiconductor, were studied. Alloys studied were demonstrated to be the band ferromagnets. Their high-field (H > 11 kOe) magnetization is described in the Stoner models with the Rhodes–Wohlfarth parameter p_RW = 1.3 for Mn_1.99Co_0.96Al_1.05 and p_RW = 2.3 for Mn_1.79Co_1.25Al_0.96. When the composition deviates from the stoichiometric Mn₂CoAl, the spontaneous moment decreases slightly, the effective moment, on the contrary, increases. In this case, a negative sign of the temperature-independent component of the paramagnetic susceptibility is observed. The density of states n(E_F) at Fermi level and the Debye temperature Θ_D of studied alloys have the usual values for 3d-metal alloys. (author)