137 research outputs found
Magnetic properties of epitaxial Fe films on MnPt/Fe(1 0 0)
No full textMagnetic properties of epitaxial Fe films on MnPt/Fe(1 0 0) were measured using X-ray magnetic circular dichroism (XMCD) and Mott electron spin polarimetry (SP). Surface sensitive secondary electron spin polarization images revealed the magnetization orientation of the Fe overlayers with respect to that of the substrate Fe crystal that was measured with bulk-sensitive XMCD. The magnetic domains of the Fe overlayer are influenced by the substrate magnetic domain structure, giving a clear evidence of the magnetic interaction between the Fe overlayer and the substrate Fe through the antiferromagnetic MnPt film. (C) 2007 Elsevier B.V. All rights reserved
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 Focusing mainly on the authors' own work, but not exclusively, published/unpublished XPEEM and MFM images of ferroic domains and complex magnetic textures (involving vortices and phase separation) are presented.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
Evidence for in-plane spin-flop orientation at the MnPt Fe (100) interface revealed by x-ray magnetic linear dichroism
No full textX-ray magnetic linear and circular dichroism at the Mn L2,3 edges are used to determine the magnetic properties of epitaxial MnPt films on Fe(100). The good agreement between experimental linear dichroism and multiplet calculations reveals that the Mn spins are aligned in plane but perpendicularly to the underlying in-plane Fe spins. The absence of magnetic circular dichroism rules out the presence of uncompensated Mn spins at the interface
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
Surface treatments and magnetic properties of Ga1−xMnxAs thin films
No full textAs a diluted magnetic semiconductor (DMS), (Ga,Mn)As is a possible candidate for the realization of spintronics devices, due to its intrinsic compatibility with GaAs based electronics. The low Curie temperature still limits its use for practical devices. Despite the huge knowledge on GaAs surface, the (Ga,Mn)As surface is still not well understood and difficult to handle. Standard surface cleaning techniques have many drawbacks, mainly because thermal treatments changes crystal structure. We will compare the magnetic and spectroscopic properties of differently processed (Ga,Mn)As surfaces with X-ray photoemission (XPS), X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD). Samples as-grown, chemically etched, Ar+ sputtered and annealed in oxygen will be compared
Giant and reversible extrinsic magnetocaloric effects in La0.7Ca0.3MnO3 films due to strain
No full textLarge thermal changes driven by a magnetic field have been proposed for environmentally friendly energy-efficient refrigeration, but only a few materials that suffer hysteresis show these giant magnetocaloric effects. Here we create giant and reversible extrinsic magnetocaloric effects in epitaxial films of the ferromagnetic manganite La0.7Ca0.3MnO3 using strain-mediated feedback from BaTiO3 substrates near a first-order structural phase transition. Our findings should inspire the discovery of giant magnetocaloric effects in a wide range of magnetic materials, and the parallel development of nanostructured bulk samples for practical applications
Control of the antiferromagnetic domain configuration and Néel axis orientation with epitaxial strain
No full textIn the growing field of spintronic devices incorporating antiferromagnetic materials, control of the domain configuration and Néel axis orientation is critical for technological implementations. Here we show by X-ray magnetic linear dichroism in photoelectron emission microscopy how antiferromagnetic properties of LaFeO3 (LFO) thin films can be tailored through epitaxial strain. LFO films were grown via molecular beam epitaxy with precise stoichiometric control, using substrates that span a range of strain states—from compressive to tensile—and crystal symmetries, including different crystallographic orientations. First, we show that epitaxial strain dictates the Néel axis orientation, shifting it from completely in-plane under compressive strain to completely out-of-plane under tensile strain, regardless of the substrate crystal symmetry. Second, we find that LFO films grown on cubic substrates exhibit a fourfold distribution of antiferromagnetic domains, but can be controlled by varying the substrate miscut, while those on orthorhombic substrates, regardless of strain state, form large-scale monodomains, a highly desirable feature for spintronic applications
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