Compensated ferrimagnets 1,2 with two inequivalent magnetic sublattices can exhibit finite spin polarization, anomalous Hall effect and tunneling magnetoresistance like a ferromagnet, even when the net magnetization exactly vanishes at the magnetic compensation point. This material class has attractive potential for high-density, ultrafast, and low-power spintronic applications. Cubic Mn2RuxGa (MRG) is a typical example of compensated ferrimagnet with high spin polarization and high tunability of compensation temperature by freely varying the Ru content x over a broad range (0.3 < x < 1.0) 3. Here, we systematically studied MRG-based polycrystalline ingots prepared by arc melting, followed by annealing at 1073 K for seven days. We surprisingly found that, in equilibrium bulk form, the cubic structure is unstable when x < 0.75, which substantially reduces the tunability of MRG. We concluded that previously reported Ru-deficient MRG thin films are mostly metastable. At equilibrium, MRG can never compensate below ~350 K.
To overcome this limitation, we alloy MRG with a fourth element V, which helps to stabilize the cubic structure while providing less valence electron than Mn and Ru. We systematically investigate the Mn2Ru0.75VyGa quaternary system. Figure 1(a) shows the temperature dependence of magnetization M(T) measured with a small applied magnetic field of 0.1 T. Adding V consistently reduces the compensation temperature from 380 K to 260 K. For y = 0.1, the M-H loop at 300 K in Fig. 1(b) shows a modest increase of the coercivity (< 0.1 T) due to the vanishing net magnetization. The sign reversal of the anomalous Hall effect (AHE) shown in Fig. 2 provides another evidence that the magnetic compensation has indeed achieved near 300 K. In the talk, we will also discuss the effect of V doping on the intrinsic and extrinsic contributions of AHE.
1 Joseph Finley and Luqiao Liu, Applied Physics Letters, 116, 110501 (2020) 2 Se Kwon Kim et al., Nature Materials, 21, 24-34 (2022) 3 H. Kurt et al., Physical Review Letters, 112, 027201 (2014)