FeRh is a unique alloy which shows temperature dependent phase transition magnetic properties. The lattice parameter (a) of this CsCl-type (B2) structure is 4.1712 Å. It undergoes a first order transition from antiferromagnetic (AFM) to ferromagnetic (FM) order at around 370K and hysteretic behavior while cooling and heating. This meta-magnetic transition of FeRh is accompanied by an isotropic expansion in the unit cell volume, which indicates strong coupling between magnetic and structural properties of FeRh. Consequently, the magnetic and transport properties, such as magnetoresistance (MR), are changed during the transition. Due to its unique thermo-magnetic behaviors, FeRh is very important for future spintronic devices. The structure could be applicable for MR devices such as memory, sensors, and many other applications. It is critical to understand how to systematically influence phase transition of FeRh from naturally applied strains. Here, we investigate magnetic properties of FeRh in different strain environments induced by the substrates with different lattice parameters. The study was performed using synchrotron radiation, temperature dependent magnetometry, and magnetic scanning probe microscopy in addition to Landau theory calculations. We found that the naturally induced strains could modulate the magnetic phase locally and globally. The presence of the segments from the nucleation of the ferromagnetic domains, with a very thin layer in the antiferromagnetic matrix and the domain growth, were observed gradually. Using the systematic phenomena, it could be used for immediate applications in the future generation of phase change random access memory (PC-RAM) devices.

Two-dimensional (2D) layered double hydroxides (LDHs) are promising as an effective electrocatalyst towards oxygen evolution reaction (OER), but their poor conductivity and tendency to stack together limits their activity and durability as an electrocatalyst. Herein, a three-dimensional (3D) core–shell catalyst, in which numerous LDH nanoplates are vertically grown on cuboidal metal organic framework (MOF) structures, is synthesized through a facile one-pot reaction strategy. The representative electrocatalyst (CoNi-BDC@LDH) achieves an excellent OER performance (with an overpotential of 282 mV at 100 mA cm−2) and stability. A series of quasi-operando and ex-situ characterization reveals a lattice oxygen-mediated mechanism where Ni and its neighboring metal site collaboratively forms Ni-O-O-M (M = Ni, Co) bridges, and the high valence state of Ni facilitates O2 desorption from the bridges. The high OER performance is additionally attributed to γ-NiOOH and CoOOH phases, and a large electrochemically active surface area.

The spectroscopic analysis of X-ray magnetic circular dichroism (XMCD), which serves as strong and element-specific magnetic contrast in full-field magnetic transmission soft x-ray microscopy, is shown to provide information on the local distribution of spin (S) and orbital (L) magnetic moments down to a spatial resolution of 25 nm limited by the x-ray optics used in the x-ray microscope. The spatially resolved L/S ratio observed in a multilayered (Co 0.3 nm/Pt 0.5 nm) × 30 thin film exhibiting a strong perpendicular magnetic anisotropy decreases significantly in the vicinity of domain walls, indicating a non-uniform spin configuration in the vertical profile of a domain wall across the thin film. Quantitative XMCD mapping with x-ray spectro-microscopy will become an important characterization tool for systems with topological or engineered magnetization inhomogeneities.

We demonstrate the possibility to tune the saturation magnetization, coercivity, and uniaxial in-plane anisotropy constant in amorphous bilayers and multilayers of Co85 (Al70Zr30)15 and Sm11Co82Ti7 through the interface density. From magnetometry and x-ray circular dichroism (XMCD) measurements, we conclude that the easy-axis coercivity μ0 Hc increases four times when the number of bilayer repetitions, N, increases from 1 to 10 within a constant total sample thickness of 20 nm. At the same time, the anisotropy constant Ku also increases by a factor four, whereas the saturation magnetization Ms decreases slightly. The Co spin and orbital moments, ms and ml, are found to be approximately constant within the sample series. The average total Co moment is only 0.8-0.9 μB/atom, but the ml/ms ratio is strongly enhanced compared to pure Co. Magnetization curves extracted from XMCD measurements show that the Co and Sm moments are ferromagnetically coupled for all samples.

BaSnO3 is an excellent candidate system for developing a new class of perovskite-based dilute magnetic semiconductors. In this study, we show that BaSn0.95Fe0.05O3 can be grown from a background pressure of ∼2×10−3 mTorr to oxygen pressures of 300 mTorr with high crystallinity and excellent structural quality. When grown in vacuum, the films may be weakly ferromagnetic with a nonzero x-ray magnetic circular dichroism signal on the Fe L3 edge. Growth with oxygen flow appears to suppress magnetic ordering. Even for very thick films grown in 100 mTorr O2, the films are paramagnetic. The existence of ferromagnetism in vacuum-grown BaSnO3 may be attributed to the F-center exchange mechanism, which relies on the presence of oxygen vacancies to facilitate the ferromagnetism. However, other possible extrinsic contributions to the magnetic ordering, such as clusters of Fe3O4 and FeO or contamination can also explain the observed behavior.

We have synthesized transparent, conducting, paramagnetic stannate thin films via rare-earth doping of BaSnO3. Gd3+ (4f7) substitution on the Ba2+ site results in optical transparency in the visible regime, low resistivities, and high electron mobilities, along with a significant magnetic moment. Pulsed laser deposition was used to stabilize epitaxial Ba0.96Gd0.04SnO3 thin films on (001) SrTiO3 substrates, and compared with Ba0.96La0.04SnO3 and undoped BaSnO3 thin films. Gd as well as La doping schemes result in electron mobilities at room temperature that exceed those of conventional complex oxides, with values as high as 60 cm2/V·s (n = 2.5 × 1020cm-3) and 30 cm2/V·s (n = 1 × 1020cm-3) for La and Gd doping, respectively. The resistivity shows little temperature dependence across a broad temperature range, indicating that in both types of films the transport is not dominated by phonon scattering. Gd-doped BaSnO3 films have a strong magnetic moment of ∼7 μB/Gd ion. Such an optically transparent conductor with localized magnetic moments may unlock opportunities for multifunctional devices in the design of next-generation displays and photovoltaics.

Structural and chemical order impact magnetic properties of solids, which are governed by spin-orbit coupling and exchange interaction. The ordered L1₀ phase of FePt is a key material to heat-assisted magnetic recording; to enable high storage density, a solid understanding is needed of structural and chemical disorder at small length scales, as well as associated modifications of the electronic band structure. Here, we investigate the effect of boron and copper additions (≲6 mol% Cu) on structural and magnetic properties of L1₀ FePt granular media. Two copper-driven mechanisms, although competing, can lead to improvements in both structural and magnetic properties. In particular, the Cu substitution on the Fe-site leads to a degradation of magnetic properties due to the delocalized electron orbitals originating from a larger Cu d-orbital occupancy. At the same time, Cu substitution leads to an enhanced crystallographic order and consequently magneto-crystalline anisotropy, which offsets the former effect to a large extent. Our study is based on magnetometry, x-ray absorption spectroscopy, ab-initio calculations and a phenomenological theory of disordered FePt granular media. We do not observe a sizable modification to Fe moments and electronic configuration; Cu reveals two different resonances associated with the presence and absence of Cu-B bonds that vary with total Cu concentration.

We study the effect of carbon segregants on the spin and orbital moments of L10 FePt granular media using x-ray magnetic circular dichroism (XMCD) spectroscopy and report an effective decoupling of the structural film properties from the magnetic parameters of the grains. The carbon concentration reduces the grain size from (200 ± 160) nm2 down to (50 ± 20) nm2 for 40 mol. %C and improves sphericity and the order of grains, while preserving the crystalline order, spin and orbital moments, and perpendicular magnetocrystalline anisotropy. We identify the primary cause of enhanced saturation and coercive fields as the reduced demagnetization fields of individual grains. The ability to shrink grains without impairing their magnetic properties is a critical requirement for the commercialization of Heat-Assisted Magnetic Recording.

Chiral magnetic domain walls are of great interest because lifting the energetic degeneracy of left- and right-handed spin textures in magnetic domain walls enables fast current-driven domain wall propagation. Although two types of magnetic domain walls are known to exist in magnetic thin films, Bloch- and Néel-walls, up to now the stabilization of homochirality was restricted to Néel-type domain walls. Since the driving mechanism of thin-film magnetic chirality, the interfacial Dzyaloshinskii-Moriya interaction, is thought to vanish in Bloch-type walls, homochiral Bloch walls have remained elusive. Here we use real-space imaging of the spin texture in iron/nickel bilayers on tungsten to show that chiral domain walls of mixed Bloch-type and Néel-type can indeed be stabilized by adding uniaxial strain in the presence of interfacial Dzyaloshinskii-Moriya interaction. Our findings introduce Bloch-type chirality as a new spin texture, which may open up new opportunities to design spin-orbitronics devices.

Perpendicular magnetic anisotropy (PMA) has recently been shown to emerge at interfaces of 3d and 5d transition-metal oxides (TMOs). However, strategies to systematically stabilize such interface-driven PMA still remains elusive, hindering further applications of this design approach. Here, tuning crystal symmetry is shown to be an effective means to engineer this interfacial phenomenon. The evolution of PMA strength as a function of ferromagnetic oxide thickness quantitatively reveals the competition between volume- and interface-specific contributions that determine the magnetic anisotropy. By applying different degrees of epitaxial strain, the relative contributions to PMA are modulated, clearly revealing their correlations with crystal symmetries. To be more specific, the volume anisotropy energy is found to be correlated with the tetragonal distortion of the ferromagnetic layer, while the interface anisotropy energy is mainly modulated by the octahedral tilting at the interface. With these insights, superlattices with enhanced interface-driven PMA and higher Curie temperature are realized. These findings reveal a route to engineering interface-driven PMA and associated magnetic phenomena in TMO heterostructures for future spintronic applications.