Abstract
With the realization of stress-induced perpendicular magnetic anisotropy, efficient spin-orbit torque switching, and room temperature topological Hall effect, interest in rare earth iron garnets has been revived in recent years for their potential in spintronic applications. In this study, we investigate the magnetic properties of micrometer-thick Bi and Ga substituted thulium iron garnets (BiGa:TmIG) grown by the liquid-phase epitaxy method. Above the magnetization compensation (MC) temperature, anomalous triple hysteresis is observed in BiGa:TmIG/Pt heterostructures by anomalous Hall effect measurements. X-ray magnetic circular dichroism and energy dispersive spectroscopy measurements reveal its origin as an internal exchange bias (EB) effect arising from inhomogeneities localized at the surface of the film. Possibly depending on the difference in thickness and defect realization of the EB layer, two types of magnetization reversal mechanisms, namely, the Stoner-Wohlfarth type and the reversible domain-wall motion type, are observed. Our results show that rich meta-magnetic phases exist in garnets close to MC, which can be robustly tuned by chemical composition engineering and conveniently probed by electrical transport measurements.
Highlights
In ferrimagnetic (FI) rare earth-transition metal (RE-TM) alloys and compounds, the magnetic moments of the REs (Gd, Tb, Tm, etc.) and the TMs (Fe, Co and Ni) are antiferromagnetically (AF) coupled to each other
Soft x-ray Fe L3 and Tm M5 peaks were first identified by saturating the magnetization in the OP direction while scanning the x-ray energy, and Fe and Tm sublattice hysteresis were obtained by sweeping the external field with x-ray energy fixed at the peak of the x-ray magnetic circular dichroism (XMCD) at the L3 and M5 edges
The 24 Fe3+ (d) ions at tetrahedral sites are AF coupled with the 16 Fe3+ (a) ions at octahedral sites, and the moments of the 24 Tm3+ (c) ions at dodecahedral sites are antiparallelly aligned with Fe3+ (d) ions, both by superexchange interaction through the O2− ions [27]
Summary
In ferrimagnetic (FI) rare earth-transition metal (RE-TM) alloys and compounds, the magnetic moments of the REs (Gd, Tb, Tm, etc.) and the TMs (Fe, Co and Ni) are antiferromagnetically (AF) coupled to each other. By changing composition or temperature, the RE and TM moments can cancel each other, resulting in a vanishing net magnetization. In the past few years, enhanced spin-orbit field [2], fast domain-wall motion [3], and ultrafast magnetization switching [4] have been demonstrated in RE-TM alloys close to compensation. Compared with these alloys, FI rare earth iron garnets (ReIG) have much higher chemical stability and lower Gilbert damping. Partly because stoichiometric TmIG does not compensate above 1.5 K [8,9], phenomena around compensation have not been well explored
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