A major aim of research in spintronics—devices that manipulate, store, and read electron spin and charge—is to understand dynamic interactions between spin transport and magnetic textures. Ferromagnet/antiferromagnet heterostructures are of particular interest, offering great potential for high-performance devices not bound by Moore’s Law.
However, while the dynamic properties of antiferromagnetic spintronics lead to greater stability and faster intrinsic switching speeds than conventional spintronics, they are notoriously difficult to measure. In a recent paper, researchers presented a new technique that enables time-resolved, direct detection of spin currents in either ferromagnetic or antiferromagnetic materials at GHz frequencies.
“For decades now, our research community has leveraged the chemical sensitivity of dichroic x-ray absorption to investigate the equilibrium magnetic properties of materials,” said staff scientist Padraic Shafer, who leads the ALS Dichroism Program. “And for the past decade, we have also pushed boundaries in measuring ferromagnet dynamics, including spin-current propagation and spin-transfer torque, which have spurred developments in magnetic data storage and processing. But no one had been able to look at these effects inside antiferromagnets.”
The work builds upon two foundational techniques at Advanced Light Source (ALS) Beamline 4.0.2: x-ray magnetic linear dichroism (XMLD) and x-ray-detected ferromagnetic resonance (XFMR). XMLD can detect the unique direction along which magnetic moments (e.g., electron spins) align within an antiferromagnet. XFMR uses the timing of synchrotron x-ray pulses to measure—with picosecond resolution—the instantaneous spin direction in an oscillating magnetic field.
Christoph Klewe, an ALS project scientist and lead author of the paper, performed experiments and modeling to explain the results of the technique, dubbed XMLD-FMR. “For this study,” said Klewe, “we focused on the ferrimagnet, NiZnAl-ferrite, a high-quality oscillator that provided a large dynamic XMLD signal for development work, plus a large dynamic ferromagnetic signal for control experiments using conventional XFMR.”
Shafer added, “An important contribution to this work was developing and validating the models that incorporate the time-dependence of the magnetic spins and the many degrees of freedom in the geometry of the experiments. As a result, all researchers can use XMLD-FMR to study spin dynamics in antiferromagnetic materials with confidence in their results.”
C. Klewe, S. Emori, Q. Li, M. Yang, B.A. Gray, H.-M. Jeon, B.M. Howe, Y. Suzuki, Z.Q. Qiu, P. Shafer, and E. Arenholz, “Experimental realization of linearly polarized X-ray detected ferromagnetic resonance,” New J. Phys. 24, 013030 (2022), doi:10.1088/1367-2630/ac465f.