Abstract:
The paper considers the question of the exchange interaction of localized spin states of Eu impurities in the Dirac semimetal $\alpha$-Cd$_3$As$_2$ by means donor electrons originating from these impurities. Being in a state of chemical compression, the divalent europium ion is inclined, by donating an electron to the conduction band, to pass into a trivalent state with a smaller ionic radius. The existence of europium in the non-magnetic trivalent state occurs only a small part of the time. However, it leads to a slight decrease in its effective local magnetic moment and an increase in the $g$-factor due to interaction with Dirac electrons. The change in the degree of chemical compression with temperature explains the previously observed temperature dependences of the $g$-factor and EPR linewidth for impurity Eu$^{2+}$ ions ($g\sim$ 2.2 and $g\sim$ 4.4). Taken together, this indicates the presence of a crystallographically selective indirect exchange interaction between localized spins of Eu$^{2+}$ ions mediated by the donor conduction electrons.
Keywords:magnetic resonance, Dirac semimetals, magnetic impurities, exchange interaction.