Speaker
Description
Noncollinear spin structures have received tremendous interest in recent years as they
provide a versatile platform for spin control and manipulation desirable for spintronics1.
Realization of noncollinearity in ferrimagnetic insulators is of particular interest as the
combined effect of both ferro- and antiferromagnetic orders opens up opportunities for their potential utilization in low-damping spintronic devices with desirable magnetic order and minimal stray fields2.
Inverse spinel nickel ferrite is a classical ferrimagnetic insulator with a collinear in-plane magnetic structure3. The substitution of Zn and Al in the nickel ferrite (NiZAF) makes it an excellent choice especially for low-damping spintronics4. However, the realization of noncollinearity together with low-damping has remained challenging so far. Here we show
the evidence of noncollinearity in the ultrathin films (3-5 nm thickness) of NiZAF induced by the rare earth ion Dy3+-doping. Motivated by our in-house laboratory measurements (SQUID and MOKE) and XMCD experiments using synchrotron x-rays, we performed soft x-ray resonant magnetic reflectivity (XRMR)5 and related simulations to probe the magnetic depth profile. The magnetic asymmetry analysis for the Fe-L3 edge (Fig. 1a) using Dyna software shows nice agreement for a model considering an in-plane spiral-type spin structure with weak out-of-plane magnetization component, confirming the noncollinear (and noncoplanar) spin- configuration in the Dy-doped NiZAF. This spiral spin structure for the Fe-spins is sketched in Fig. 1b. We attribute the stabilization of such noncollinearity to the formation of a local strain field created by the Dy3+ (evidenced by Dy-L3 EXAFS analysis) thereby involving local space- inversion symmetry breaking and emergence of asymmetric Dzyaloshinskii-Moriya interaction.This is supported by our first-principle DFT calculations.
The realization of noncollinear spin structure in the insulating spinel-ferrite opens further pathway to explore the possibility of chiral magnetic domain and topological spin textures (e. g., skyrmions) potential for the oxide-based spintronic applications.
This work is supported by the DFG (grant no. Mo 4198/2-1) and FWF (grant no. I-5384).
REFERENCES
[1]. A. Fert, N. Reyren and V. Cros, Nat. Rev. Mater. 2, 17031 (2017). [2]. S. K. Kim et al. Nat. Mater. 21, 24-34 (2022).
[3]. Y. Yafet and C. Kittel, Phys. Rev. 87, 290-294 (1952). [4]. S. Emori et al., Adv. Mater. 29, 1701130 (2017).
[5]. J.-M. Tonnerre et al., Eur. Phys. J. -Spec. Top. 208, 177-187 (2012)
