Field-induced magnetostructural phase transition in double perovskite Ca₂FeReO₆ studied via x-ray magnetic circular dichroism

Spin and orbital contributions to the magnetic moment of rhenium have been studied across the magnetostructural transition in Ca₂FeReO₆ double perovskite employing x-ray magnetic circular dichroism (XMCD) at the Re L_2,3 edges. Temperature-dependent measurements performed in pulsed magnetic field varying from 6.8 to 30 T revealed that the two phases of this compound are characterized by a different spin-orbit coupling. At T=10 K, the average orbital-to-spin moment ratio of the Re sublattice increases in the application of 30 T magnetic field by ∼5%, while at T=250 K it is field independent and amounts to |m_L/m_S|=0.362(6). The field and temperature dependences of the rhenium XMCD and bulk magnetization are explained within the scenario of a field-induced phase coexistence and transition between two monoclinic phases of diverse magnetocrystalline coupling.