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The multilayer thin films consisting of alternating stacks of ferromagnetic Permalloy (Py) and ultra thin non-magnetic (sub-nanometer) spacer (Cr) layers have been investigated by using ferromagnetic resonance (FMR) and dc magnetization measurement techniques. The non-magnetic spacer layer thickness changes from 0.5 Å to 2.5 Å by 0.5 Å steps. Polycrystalline composite metallic films were grown on Si substrate by usual magnetron sputtering techniques at UHV conditions. The magnetic hysteresis curves were recorded by conventional dc magnetization. The ac and dc magnetic properties were investigated by using ferromagnetic resonance. FMR measurements were carried out for different directions of external dc magnetic field in order to search magnetic anisotropy. Two strong and well defined peaks (acoustic and optic mode) were observed in FMR spectrum as the magnetic field direction approaches to the film normal. Their positions and relative intensities helped to characterize coupling species. The magnetic parameters have been deduced by using a theoretical model. It has been found that the exchange coupling parameter between ferromagnetic layers through non-magnetic Cr spacer is ferromagnetic in nature and strongly decreases with increasing spacer layer thickness. The magnetic anisotropy parameters strictly depend on magnetic layer thickness while the dc magnetization is almost constant for a few nanometer thick Permalloy as well. We observed only ferromagnetic coupling between ferromagnetic layers in all samples. [ABSTRACT FROM AUTHOR]

High quality compact Ni nanowire (NW) arrays with aspect ratios (wire length/diameter) varying between 70-171 for a wire length of ∼6 μm, and between 3-400 for a constant wire diameter of 60 nm were successfully grown by direct current electrodeposition into free standing porous alumina templates having a lattice constant, i.e., interpore distance, of 105 nm. The NWs have been investigated using a combination of scanning- and transmission-electron microscopies, selected-area electron diffraction, x-ray diffraction analysis, ferromagnetic resonance (FMR), and vibration sample magnetometer techniques at room temperature. Microscopic and diffraction results show that the wires are uniform and mostly single-crystalline, being 220-oriented along the growth direction. Magnetic properties of samples are heavily dependent on the wire length as well as the diameter or packing factor, P (the volume fraction of wires/template). The FMR spectra and the field orientation dependence of the resonance field values were fitted using the imaginary part of magnetic susceptibility and a dispersion relation of magnetization, including the Bloch-Bloembergen type damping term. Combined with hysteresis (M-H) results, these indicate that the preferred (easy) axis of magnetization is parallel to the NW-axis for P<33%. On the other hand, strong interwire exchange interactions are determined to supply a magnetization state with preferred axis perpendicular to the wires for samples with P>33%. Comparison with relatively thick (110 nm diameter) and loosely packed (P∼10%) Ni NW arrays suggest that the magnetization reversal mechanism could be that of curling type. [ABSTRACT FROM AUTHOR]

Magnetic properties of ultrathin Py/Cr/Py trilayers have been investigated as a function of Cr spacer layer thickness by using ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques. The Cr spacer layer thickness was increased from 4 to 40 Å with 1 Å steps to determine the dependence of interlayer exchange coupling between ferromagnetic layers on the spacer layer thickness. Two strong and well resolved peaks were observed which correspond to a strong (acoustic) and weak (optic) modes of magnetization precession in the effective dc field due to the exciting external microwave field as the external dc field orientation comes close to the film normal. The separation of the two modes in the field axis depends on the thickness of Cr spacer layer. An interchange in the relative positions of the acoustic and optic modes has been observed for a particular thickness of Cr spacer layer as well. A computer program for magnetically exchange coupled N magnetic layers was written to simulate the experimental FMR spectra and to obtain the magnetic parameters of ultrathin Py/Cr/Py trilayers. FMR data have been analyzed from every aspect by using this program and interlayer exchange coupling constant was calculated for the prepared structures. It was found that the relative position of the peaks depends on the nature (sign) of the interlayer exchange coupling between ferromagnetic layers through Cr spacer layer. In Py/Cr/Py trilayers, strength of the interlayer exchange coupling constant oscillates and changes its sign with Cr spacer layer thickness with a period of about 11 Å. [ABSTRACT FROM AUTHOR]

Magnetic anisotropies of epitaxial ultrathin iron films grown on the surface-reconstructed GaAs substrate were studied. Ferromagnetic resonance technique was exploited to determine magnetic parameters of the films in the temperature range of 4–300 K. Extraordinary angular dependence of the FMR spectra was explained by the presence of fourfold and twofold in-plane anisotropies. A strong in-plane uniaxial anisotropy with magnetic hard axis along the [110] crystallographic direction is present at the GaAs/Fe(001) interface while a weak in-plane uniaxial anisotropy for the Fe grown on Au has its easy axis oriented along [110]. A linear dependence of the magnetic anisotropies as a function of temperature suggests that the strength of the in-plane uniaxial anisotropy is affected by the magnetoelastic anisotropies and differential thermal expansion of contacting materials. [ABSTRACT FROM AUTHOR]

We complement our study on the doping and disorder in Co2MnZ compounds [I. Galanakis, K. Özdoğan, B. Aktaş, and E. Şaşıoğlu, Appl. Phys. Lett. 89, 042502 (2006) and K. Özdoğan, E. Şaşıoğlu, B. Aktaş, and I. Galanakis, Phys. Rev. B 74, 172412 (2006)] to cover also the quaternary Co2[Y1-xYx*]Z compounds with the lower-valent transition metals Y, Y* being Cr, Mn, or Fe and the sp atom Z being one of Al, Ga, Si, Ge, and Sn. This study gives a global overview of the magnetic and electronic properties of these compounds since we vary both Y and Z elements. Our results suggest that for realistic applications the most appropriate compounds are the ones belonging to the families Co2[Mn1-xCrx]Z with x>0.5 irrespectively of the nature of the sp atoms since they combine high values of majority density of states at the Fermi level due to the presence of Cr, and half-metallicity with large band gaps. On the other hand, the presence of Fe considerably lowers the majority density of states at the Fermi level and when combined with an element belonging to the Si column, it can even destroy half-metallicity. [ABSTRACT FROM AUTHOR]