We report element specific structural and magnetic investigations on Zn(1-x)Co(x)O epitaxial films using synchrotron radiation. Co dopants exclusively occupy Zn sites as revealed by x-ray linear dichroism having an unprecedented degree of structural perfection. Comparative magnetic field dependent measurements by x-ray magnetic circular dichroism and conventional magnetometry consistently show purely paramagnetic behavior for isolated Co dopant atoms with a magnetic moment of 4.8 (mu B). However, the total magnetization is reduced by approximately 30%, demonstrating that Co-O-Co pairs are antiferromagnetically coupled. We find no sign of intrinsic ferromagnetic interactions for isolated or paired Co dopant atoms in Co:ZnO films.
High entropy oxides (HEOs) are single-phase solid solutions consisting of 5 or more cations in approximately equiatomic proportions. In this study, we show the reversible control of optical properties in a rare-earth (RE) based HEO-(Ce0.2La0.2Pr0.2Sm0.2Y0.2)O2−δ and subsequently utilize a combination of spectroscopic techniques to derive the features of the electronic band structure underpinning the observed optical phenomena. Heat treatment of the HEO under a vacuum atmosphere followed by reheat treatment in air results in a reversible change in the bandgap energy, from 1.9 eV to 2.5 eV. The finding is consistent with the reversible changes in the oxidation state and related f-orbital occupancy of Pr. However, no pertinent changes in the phase composition or crystal structure are observed upon the vacuum heat treatment. Furthermore, annealing of this HEO under a H2 atmosphere, followed by reheat treatment in air, results in even larger but still a reversible change in the bandgap energy from 1.9 eV to 3.2 eV. This is accompanied by a disorder–order type crystal structure transition and changes in the O 2p–RE 5d hybridization evidenced from x-ray absorption near-edge spectra (XANES). The O K and RE M4,5/L3 XANES indicate that the presence of Ce and Pr (in 3+/4+ states) leads to the formation of intermediate 4f energy levels between the O 2p and the RE 5d gap in HEO. It is concluded that heat treatment under reducing/oxidizing atmospheres affects these intermediate levels, thus offering the possibility to tune the bandgap energy in HEOs.
We study the spin Hall magnetoresistance effect in ferrimagnet/normal metal bilayers, comparing the response in collinear and canted magnetic phases. In the collinear magnetic phase, in which the sublattice magnetic moments are all aligned along the same axis, we observe the conventional spin Hall magnetoresistance. In contrast, in the canted phase, the magnetoresistance changes sign. Using atomistic spin simulations and x-ray absorption experiments, we can understand these observations in terms of the magnetic field and temperature dependent orientation of magnetic moments on different magnetic sublattices. This enables a magnetotransport based investigation of noncollinear magnetic textures. DOI: 10.1103/PhysRevB.94.094401The magnetic properties of ferromagnets are often modeled in terms of a simple macrospin with magnetization vector M. In this picture, one tacitly assumes that all individual atomic magnetic moments μ are aligned in one direction, such that the magnetization is M = nμ with the moment number density n. However, many magnets exhibit a much richer magnetic structure, with canted, spiral, frustrated, or even topological [1,2] phases appearing in addition to collinear magnetic order. Unravelling these experimentally typically requires sophisticated methods, e.g., spin polarized neutron scattering, x-ray magnetic circular dichroism, or Lorentz transmission electron microscopy. A pathway for the electrical detection of magnetic properties is provided by spin torques arising at a magnet/metal interface [3][4][5]. These torques govern fundamental spintronic phenomena such as spin pumping [6][7][8][9][10], spin Seebeck effect [11][12][13], as well as spin Hall magnetoresistance [14][15][16][17][18], and even enable an electrical control of the magnetization in magnetic nanostructures [3][4][5]. However, while the spin torque effect-or more precisely the transfer of spin angular momentum across the magnet/metal interface-has been extensively discussed for a macrospin M [19,20], the action of spin torques on noncollinear magnetic phases is only poorly understood.Here we show that in the ferrimagnet gadolinium iron garnet (Gd 3 Fe 5 O 12 , GdIG), the spin Hall magnetoresistance (SMR) can be used to resolve the orientation of magnetic moments residing on different magnetic sublattices. We thereby prove that the SMR is not just governed by the net moment μ net = μ (viz. the corresponding macrospin magnetization * Present address: Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany; goennenwein@ wmi.badw.de M net ) aligned along the externally applied magnetic field. This is reflected most conspicuously by the SMR sign inversion observed for canted sublattice moments. The interpretation of our experiments is corroborated by x-ray magnetic circular dichroism (XMCD) measurements, and atomistic spin simulations [13] suggesting that the Fe sublattice moments dominate the SMR response.The SMR originates from spin current transport across the interface between an (insulating) ma...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.