The magnetic structure of exchange-coupled antiferromagnetic (AF) layers in epitaxial La 0.7 Sr 0.3 MnO 3 (LSMO)/La 0.7 Sr 0.3 FeO 3 (LSFO) superlattices grown on (111)-oriented SrTiO 3 substrates was studied using angle-dependent x-ray absorption spectroscopy utilizing linearly polarized x rays. We demonstrate the development of the measurement protocols needed to determine the orientation of the LSFO antiferromagnetic spin axis and how it responds to an applied magnetic field due to exchange interactions with an adjacent ferromagnetic layer. A small energy difference exists between two types of AF order: the majority of the AF moments cant out-of-the-plane of the film along the 110 or 100 directions depending on the LSFO layer thickness. In response to an applied magnetic field, these canted moments are aligned with a single 110 or 100 direction that maintains a nearly perpendicular orientation relative to the LSMO sublayer magnetization. The remaining AF moments lie within the (111) plane and these in-plane moments can be reoriented to an arbitrary in-plane direction to lie parallel to the LSMO sublayer magnetization. These results demonstrate that the magnetic order of AF thin films and heterostructures is far more complex than in bulk LSFO and can be tuned with orientation, thickness, and applied magnetic field.

In ferromagnetic metals, transverse spin currents are thought to be absorbed via dephasing - i.e., destructive interference of spins precessing about the strong exchange field. Yet, due to the ultrashort coherence length of ≈1 nm in typical ferromagnetic thin films, it is difficult to distinguish dephasing in the bulk from spin-flip scattering at the interface. Here, to assess which mechanism dominates, we examine transverse spin-current absorption in ferromagnetic NiCu alloy films with reduced exchange fields. We observe that the coherence length increases with decreasing Curie temperature, as weaker dephasing in the film bulk slows down spin absorption. Moreover, nonmagnetic Cu impurities do not diminish the efficiency of spin-transfer torque from the absorbed spin current. Our findings affirm that the transverse spin current is predominantly absorbed by dephasing inside the nanometer-thick ferromagnetic metals, even with high impurity contents.

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.

The ability to systematically modify the magnetic properties of epitaxial La0.7Sr0.3MnO3 thin films is demonstrated through the use of Ar+ ion implantation. With increasing implant dose, a uniaxial expansion of the c-axis of the unit cell leads to a transition from in-plane toward perpendicular magnetic anisotropy. Above a critical dose of 3 × 1013 Ar+/cm2, significant crystalline disorder exists leading to a decrease in the average Mn valence state and near complete suppression of magnetization. Combined with lithographic techniques, ion implantation enables the fabrication of magnetic spin textures consisting of adjacent regions with tunable magnetic anisotropy in complex oxide thin films.

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.

Antiferromagnetic (AFM) spintronics offer several benefits compared to their ferromagnetic (FM) counterparts, such as high storage capacity and faster processing speed, however, difficulties in manipulating and detecting the AFM moments impede their implementation. Spin-flop coupling, the interfacial perpendicular coupling between FM and AFM moments, can be utilized to control the orientation of AFM moments with the application of moderate magnetic fields on the scale of tenths of a Tesla. In this work, epitaxial bilayers of AFM La0.5Sr0.5FeO3 (LSFO)/FM La0.7Sr0.3MnO3 (LSMO) with fixed LSMO thickness (∼85 u.c.) and LSFO thicknesses varying from 10 to 50 u.c. were investigated to determine the effect of Sr doping and La1-xSrxFeO3 magnetocrystalline anisotropy on the strength of spin-flop coupling. X-ray magnetic linear dichroism demonstrated that the spin-flop coupling strength decreased with increasing LSFO layer thickness, persisting at a thickness of 50 u.c. (∼20 nm). Furthermore, photoemission electron microscopy revealed a domain-by-domain correlation between the FM and AFM domains consistent with the perpendicular orientation dictated by spin-flop coupling. These results demonstrate that LSFO/LSMO bilayers have the potential to serve as a model materials system for AFM spin transport measurements.