Resonant nanodiffraction x-ray imaging reveals role of magnetic domains in complex oxide spin caloritronics

Abstract

Spin electronic devices based on crystalline oxide layers with nanoscale thicknesses involve complex structural and magnetic phenomena, including magnetic domains and the coupling of the magnetism to elastic and plastic crystallographic distortion. The magnetism of buried nanoscale layers has a substantial impact on spincaloritronic devices incorporating garnets and other oxides exhibiting the spin Seebeck effect (SSE). Synchrotron hard x-ray nanobeam diffraction techniques combine structural, elemental, and magnetic sensitivity and allow the magnetic domain configuration and structural distortion to be probed in buried layers simultaneously. Resonant scattering at the Gd L2 edge of Gd3Fe5O12 layers yields magnetic contrast with both linear and circular incident x-ray polarization. Domain patterns facet to form low-energy domain wall orientations but also are coupled to elastic features linked to epitaxial growth. Nanobeam magnetic diffraction images reveal diverse magnetic microstructure within emerging SSE materials and a strong coupling of the magnetism to crystallographic distortion.

X-ray nanodiffraction imaging reveals distinct nanoscopic dynamics of an ultrafast phase transition

“…Ultrafast nanoscale characterization methods based on optical ( 2 , 12 – 15 ), electron ( 16 , 17 ), and X-ray ( 18 – 23 ) microscopies have been recently developed and have revealed new physical phenomena. Hard X-ray microscopy is particularly advantageous in the study of phase transformations involving structural changes because X-ray diffraction is highly sensitive to structural heterogeneity, due to its high reciprocal-space resolution ( 24 , 25 ). X-ray diffraction microscopy also preserves the spatially heterogenous stress state in complex structures such as quantum devices ( 25 – 27 ) because experiments do not require the preparation of the free-standing thin specimens typically required for transmission electron microscopy.…”

“…Hard X-ray microscopy is particularly advantageous in the study of phase transformations involving structural changes because X-ray diffraction is highly sensitive to structural heterogeneity, due to its high reciprocal-space resolution ( 24 , 25 ). X-ray diffraction microscopy also preserves the spatially heterogenous stress state in complex structures such as quantum devices ( 25 – 27 ) because experiments do not require the preparation of the free-standing thin specimens typically required for transmission electron microscopy. Here, X-ray nanodiffraction microscopy combined with ultrafast optical excitation reveals that the nanoscale processes of the optically driven first-order phase transition in FeRh thin films are distinct from those occurring in a quasi-equilibrium transformation with slowly varying external parameters.…”