Angular dependence of the magnetization reversal in exchange biased Fe/MnF2

A detailed study of exchange-biased Fe/MnF2 bilayers using magneto-optical Kerr Effect shows that the magnetization reversal occurs almost fully through domain wall nucleation and propagation for external fields parallel to the exchange bias direction. For finite angles phi between bias and external field the magnetization is aligned perpendicular to the field cooling direction for a limited field range for decreasing fields. For external fields perpendicular to the bias direction the magnetization aligns with the field cooling direction for descending and ascending fields before fully reversing. The field range for which the magnetization is close to perpendicular to the external field can be estimated using a simple effective field model.Comment: 14 pages, 3 figures, to appear in AP

Domain-resolved room-temperature magneto-electric coupling in manganite-titanate heterostructures

We present a model artificial multiferroic system consisting of a (011)-oriented ferroelectric Pb(Mg,Nb,Ti)O$_3$ substrate intimately coupled to a ferromagnetic (La,Sr)MnO$_3$ film through epitaxial strain and converse piezoelectric effects. Electric field pulse sequences of less than 6 kV/cm were shown to induce large reversible and bistable remanent strains in the manganite film. Magnetic hysteresis loops demonstrate that the changes in strain states result in significant changes in magnetic anisotropy from a highly anisotropic two-fold magnetic symmetry to a more isotropic one. Such changes in magnetic anisotropy are reversible upon multiple cycles and are stable at zero applied electric field, and are accompanied by large changes in resistivity. We directly image the change between the two-fold and isotropic magnetic configurations at the scale of a single ferromagnetic domain using X-ray photoemission electron microscopy as a function of applied electric field pulses. Imaging the domain reversal process as a function of electric field shows that the energy barrier for magnetization reversal is drastically lowered, by up to 70% as determined from free energy calculations, through the anisotropic strain change generated by the ferroelectric substrate. Thus, an electric field pulse can be used to 'set' and 'reset' the magnetic anisotropy orientation and resistive state in the film, as well as lowering the coercive field required to reverse magnetization, showing a promising route towards electric-field manipulation of multifunctional nanostructures at room temperature.Comment: 6 figures, 1 tabl

Control of the Magnetic and Magnetotransport Properties of La0.67Sr0.33MnO3 Thin Films Through Epitaxial Strain

The influence of epitaxial strain, in the form of tetragonal distortions, on the magnetic and magnetotransport properties of La{sub 0.67}Sr{sub 0.33}MnO{sub 3} thin films was studied. The tetragonal distortion (c/a ratio) was modulated through the choice of the substrate, ranging from c/a=1.007 on (001)-oriented (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7} substrates to 0.952 on (110)-oriented GdScO{sub 3} substrates. In agreement with previous theoretical predictions, these large values of tensile strain cause the Curie temperature and the saturation magnetization to decrease, alter the temperature dependence of the resistivity and magnetoresistance, and increase the resistivity several orders of magnitude

Titanium Nitride as a Seed Layer for Heusler Compounds

Titanium nitride (TiN) shows low resistivity at room temperature, high thermal stability and thus has the potential to serve as seed layer in magnetic tunnel junctions. High quality TiN thin films with regard to the crystallographic and electrical properties were grown and characterized by X-ray diffraction and 4-terminal transport measurements. Element specific X-ray absorption spectroscopy revealed pure TiN in the bulk. To investigate the influence of a TiN seed layer on a ferro(i)magnetic bottom electrode, an out-of-plane magnetized Mn2.45Ga as well as in- and out-of-plane magnetized Co2FeAl thin films were deposited on a TiN buffer, respectively. The magnetic properties were investigated using a superconducting quantum interference device (SQUID) and anomalous Hall effect (AHE) for Mn2.45Ga. Magneto optical Kerr effect (MOKE) measurements were carried out to investigate the magnetic properties of Co2FeAl. TiN buffered Mn2.45Ga thin films showed higher coercivity and squareness ratio compared to unbuffered samples. The Heusler compound Co2FeAl showed already good crystallinity when grown at room temperature

Defect-induced magnetism in graphite through neutron irradiation

We have investigated the variation in the magnetization of highly ordered pyrolytic graphite (HOPG) after neutron irradiation, which introduces defects in the bulk sample and consequently gives rise to a large magnetic signal. We observe strong paramagnetism in HOPG, increasing with the neutron fluence. We correlate the induced paramagnetism with structural defects by comparison with density-functional theory calculations. In addition to the in-plane vacancies, the trans-planar defects also contribute to the magnetization. The lack of any magnetic order between the local moments is possibly due to the absence of hydrogen/nitrogen chemisorption, or the magnetic order cannot be established at all in the bulk form.Comment: 10 pages, 8 figure

Anisotropic x ray magnetic linear dichroism - Its importance for the analysis of soft x ray spectra of magnetic oxides

Using spectroscopic information for x ray magnetometry and magnetic microscopy requires detailed theoretical understanding of spectral shape and magnitude of dichroism signals. We have shown unambiguously that--contrary to common belief--spectral shape and magnitude of x ray magnetic linear dichroism (XMLD) are not only determined by the relative orientation of magnetic moments and x ray polarization, but also their orientations relative to the crystallographic axes must be taken into account for accurate interpretation of XMLD data