Electrical detection of magnetization canting in a magnetic insulator
In addition to collinear magnetic order, magnetic materials can exhibit a large variety of other types of order, such as canted, spiral, frustrated or even topological states. However, unravelling these different magnetic structures usually requires sophisticated methods, e.g., spin-polarized neutron scattering, x-ray magnetic circular dichroism, or Lorentz transmission electron microscopy.
Here, we present a method for the electrical detection of magnetic phases based on the spin Hall magnetoresistance effect (SMR). The SMR has been extensively studied in heterostructures consisting of a collinear ferrimagnetic insulator (MI) with net magnetization M and a normal metal (NM) with large spin-orbit coupling such as Pt. Owing to the spin Hall effect, a charge current driven through the Pt is accompanied by a spin current with a spin polarization s, which is either transmitted into or reflected at the interface of the magnetic system, depending on the orientation of M. This leads to a magnetization orientation dependent modulation of the resistance in the metal – the so-called spin Hall magnetoresistance effect. We have measured the SMR in a MI/Pt bilayer based on the compensated ferrimagnet (In,Y)-doped Gd3Fe5O12 (InYGdIG) as the MI. InYGdIG assumes a canted phase around its compensation temperature Tcomp = 85 K, whereas it exhibits collinear ferrimagnetism both well above and well below Tcomp. We extract the amplitude of the SMR effect from measurements at the EMFL-Grenoble in magnetic fields up to 29 T in the collinear as well as in the canted phase, and observe a sign change (red pocket in the Figure) around Tcomp. The latter can be understood in terms of canted magnetic sublattices, as confirmed by atomistic spin calculations. Our analysis furthermore suggests that the SMR response in Gd3Fe5O12 is dominated by the iron sublattice magnetizations. Taken together, our results clearly show that the SMR is not governed by the net magnetization, but by the orientation of magnetic moments on different sublattices. This suggests that SMR experiments can be used to map out different magnetic phases in magnetic insulators.
False-color plot of the SMR amplitude in (In,Y)-doped Gd3Fe5O12/Pt measured as a function of temperature and magnetic field. A sign change of the SMR is evident as the red pocket around 85 K, where the Fe and Gd sublattice magnetizations are canted.
Spin Hall magnetoresistance in a canted ferrimagnet
K. Ganzhorn, J. Barker, R. Schlitz, B. A. Piot, K. Ollefs, F. Guillou, F. Wilhelm, A. Rogalev, M. Opel, M. Althammer, S. Geprägs, H. Huebl, R. Gross, G. Bauer and S. T. B. Goennenwein, Phys. Rev. B 94, 094401 (2016).