Magnetic nature of wolframite MgReO₄

Rhenium oxides belonging to the family AReO₄ where A is a metal cation, exhibit interesting electronic and magnetic properties. In this study we have utilized the muon spin rotation/relaxation (µ⁺SR) technique to study the magnetic properties of the MgReO₄ compound. To the best of our knowledge, this is the first investigation reported on this interesting material, that is stabilized in a wolframite crystal structure using a special high-pressure synthesis technique. Bulk magnetic studies show the onset of an antiferromagnetic (AF) long range order, or a possible singlet spin state at T_C1 ≈ 90 K, with a subtle second high-temperature transition at T_C2 ≈ 280 K. Both transitions are also confirmed by heat capacity (C_p) measurements. From our µ⁺SR measurements, it is clear that the sample enters an AF order below T_C1 = T_N ≈ 85 K. We find no evidence of magnetic signal above T_N, which indicates that T_C2 is likely linked to a structural transition. Further, via sensitive zero field (ZF) µ⁺SR measurements we find evidence of a spin reorientation at T_Cant ≈ 65 K. This points towards a transition from a collinear AF into a canted AF order at low temperature, which is proposed to be driven by competing magnetic interactions.