Magnetic properties of Mn-doped Bi₂Se₃ compound: temperature dependence and pressure effects

Magnetic susceptibility $\chi$ of Bi$_{2-x}$Mn$_{x}$Se$_3$ ($x = 0.01-0.2$) was measured in the temperature range $4.2-300$ K. For all the samples, a Curie-Weiss behaviour of $\chi(T)$ was revealed with effective magnetic moments of Mn ions corresponding to the spin value S=5/2, which couple antiferromagnetically with the paramagnetic Curie temperature $\Theta\sim -50$ K. In addition, for the samples of nominal composition $x$ = 0.1 and 0.2 the effect of a hydrostatic pressure $P$ up to 2 kbar on $\chi$ has been measured at fixed temperatures 78 and 300 K that allowed to estimate the pressure derivative of $\Theta$ to be d$\Theta$/d$P\sim-0.8$ K/kbar. Based on the observed behaviour of $\Theta$ with varied Mn concentration and pressure, a possible mechanism of interaction between localized Mn moments is discussed.