124 research outputs found
XPEEM and MFM Imaging of Ferroic Materials
No full textThe authors describe and compare two complementary techniques that are habitually used to image ferromagnetic and ferroelectric materials with sub-micron spatial resolutions (typically 50 nm, at best 10 nm). The first technique is variable-temperature photoemission electron microscopy with magnetic/antiferromagnetic/polar contrast from circularly/linearly polarized incident X-rays (XPEEM). The second technique is magnetic force microscopy (MFM). Focusing mainly on the authors' own work, but not exclusively, published/unpublished XPEEM and MFM images of ferroic domains and complex magnetic textures (involving vortices and phase separation) are presented. Highlights include the use of two XPEEM images to create 2D vector maps of in-plane (IP) magnetization, and the use of imaging to detect electrically driven local reversals of magnetization. The brief and simple descriptions of XPEEM and MFM should be useful for beginners seeking to employ these techniques in order to understand and harness ferroic materials
Low-temperature transverse magnetic domains in nominally uniaxial La0.67Sr0.33MnO3 films on NdGaO3 (0 0 1)
No full textControl of Magnetization-Reversal Mechanism via Uniaxial Anisotropy Strength in La0.67Sr0.33MnO3 Electrodes for Spintronic Devices
No full textSpintronic device performance depends critically on magnetization reversal mechanisms, but these are rarely imaged in order to verify correct operation. Here we use magnetometry and magnetic imaging to study thin films and patterned elements of highly spin-polarized La0.67Sr0.33MnO3 grown epitaxially on NdGaO3 substrates whose crystallographic orientation determines magnetic anisotropy strength. Small anisotropy yields gradual magnetization reversal via nucleation and propagation of small-needle domains, whereas large anisotropy yields a single nucleation event resulting in sharp and complete magnetization reversal. We explain these observed differences using micromagnetic simulations, and exploit them in order to quantify the effect of La0.67Sr0.33MnO3 electrode behavior on spin signals from hypothetical devices. Our work, therefore, highlights the dramatic discrepancies that can arise between the design and performance of spintronic devices
Inverted shear-strain magnetoelastic coupling at the Fe/BaTiO3 interface from polarised x-ray imaging
No full textThe elastic degree of freedom is widely exploited to mediate magnetoelectric coupling between ferromagnetic films and ferroelectric substrates. For epitaxial Fe films grown on clean BaTiO3 substrates, shear strain can determine the underlying magnetoelastic coupling. Here, we use PhotoEmission Electron Microscopy of ferroic Fe and BaTiO3 domains, combined with micromagnetic simulations, to directly reveal an inverted interfacial magnetoelastic coupling in the low-dimensional limit. We show that the magnetocrystalline anisotropy competes with the epitaxial shear strain to align the local magnetization of ultrathin Fe films close to the local polarization direction of the ferroelectric BaTiO3 in-plane domains. Poling the BaTiO3 substrate creates c-domains with no shear strain contribution with the local magnetization rotated by ~45°. Tuning shear strain magnetoelastic contributions suggests new routes for designing magnetoelectric devices
The variability of perioperative nursing care in neurosurgery patients: a national – based prospective study
No full textLarge magnetoelectric coupling in multiferroic oxide heterostructures assembled via epitaxial lift-off.
No full textEpitaxial films may be released from growth substrates and transferred to structurally and chemically incompatible substrates, but epitaxial films of transition metal perovskite oxides have not been transferred to electroactive substrates for voltage control of their myriad functional properties. Here we demonstrate good strain transmission at the incoherent interface between a strain-released film of epitaxially grown ferromagnetic La0.7Sr0.3MnO3 and an electroactive substrate of ferroelectric 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 in a different crystallographic orientation. Our strain-mediated magnetoelectric coupling compares well with respect to epitaxial heterostructures, where the epitaxy responsible for strong coupling can degrade film magnetization via strain and dislocations. Moreover, the electrical switching of magnetic anisotropy is repeatable and non-volatile. High-resolution magnetic vector maps reveal that micromagnetic behaviour is governed by electrically controlled strain and cracks in the film. Our demonstration should inspire others to control the physical/chemical properties in strain-released epitaxial oxide films by using electroactive substrates to impart strain via non-epitaxial interfaces
Evidence for a Magnetic Proximity Effect up to Room Temperature at Fe/(Ga,Mn)As Interfaces
No full textWe report x-ray magnetic circular dichroism and superconducting quantum interference device magnetometry experiments to study magnetic order and coupling in thin Fe/(Ga,Mn)As(100) films. We observe induced magnetic order in the (Ga,Mn)As layer that extends over more than 2 nm, even at room temperature. We find spectroscopic evidences of a hybridized d configuration of Mn atoms in Fe/(Ga,Mn)As, with negligible Mn diffusion and/or MnFe intermixing. We show by experiment as well as by theory that the magnetic moment of the Mn ions couples antiparallel to the moment of the Fe overlayer
Exchange-spring-driven spin flop in an ErFe2/YFe2 multilayer studied by x-ray magnetic circular dichroism
No full textVoltage control of magnetic single domains in Ni discs on ferroelectric BaTiO3
No full textFor 1 µm-diameter Ni discs on a BaTiO3 substrate, the local magnetization direction is determined by ferroelectric domain orientation as a consequence of growth strain, such that single-domain discs lie on single ferroelectric domains. On applying a voltage across the substrate, ferroelectric domain switching yields non-volatile magnetization rotations of 90°, while piezoelectric effects that are small and continuous yield non-volatile magnetization reversals that are non-deterministic. This demonstration of magnetization reversal without ferroelectric domain switching implies reduced fatigue, and therefore represents a step towards applications
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