Enhancement of uniaxial magnetic anisotropy in Fe thin films grown on GaAs(001) with an MgO underlayer

The understanding and control of anisotropy in Fe films grown on cubic systems such as GaAs and MgO has been of interest from the point of view of applications in devices. We report magnetic anisotropy studies on Fe/GaAs(001) and Fe/MgO/GaAs(001) prepared by pulsed laser deposition. In Fe/GaAs(001), magneto optical Kerr effect (MOKE) measurements revealed a dominant uniaxial anisotropy for Fe thickness less than 20 monolayers (ML) and this was confirmed by ferromagnetic resonance (FMR) studies. Multiple steps in the hysteresis loops were observed for Fe films of thickness 20 and 25 ML. Whereas, in Fe/MgO/GaAs(001), even at 25 ML of Fe, the uniaxial anisotropy remained dominant. The anisotropy constants obtained from FMR spectra have shown that the relative strength of uniaxial anisotropy is higher as compared to the cubic anisotropy constant in the case of Fe/MgO/GaAs(001). (C) 2011 American Institute of Physics. doi:10.1063/1.3556941]

Anisotropic low field magnetoimpedance in (001) oriented La0.7Sr0.3MnO3 thin films

We report the evidence for the anisotropic magnetoimpedance behavior in (001) oriented La0.7Sr0.3MnO3 (LSMO) thin films, in low frequency-low magnetic field regime. (001) oriented LSMO thin films were deposited using pulsed laser deposition and characterized with X-ray diffraction and temperature dependent magnetization studies. In the in-plain configuration, an ac magnetoresistance (MRac) of similar to -0.5% was observed at 1000 Oe, at 100 Hz frequency in these films. The MRac was found to decrease with increase in frequency. We observe increases in MRac at low frequency, indicating major contribution for change of permeability from domain wall motion. At higher frequencies, it decreases due to decrease in transverse permeability, resulting from dampening of domain wall motion. Out-of-plane configuration showed MRac similar to 5.5% at 1000 Oe, at 100 Hz frequency. The MRac turned from positive to negative with increase in frequency in out-of-plane configuration. These changes are attributed to the change in permeability of the film with the frequency and applied magnetic field.

BIMODAL NANOINDENTATION RESPONSE OF THE (001) FACE IN CRYSTALLINE SODIUM SACCHARIN DIHYDRATE

The nanoindentation response of the (001) face of sodium saccharin dihydrate is examined. The structure can be demarcated into regular and irregular regions or domains. The regular domains have solid-like and the irregular ones have liquid-like characteristics. Therefore, these domains impart a microstructure to the crystal. The indent face (001) is prominently developed in this crystal and unambiguously presents the regular and irregular regions to nanoindention. Average values of elastic modulus and hardness show a distinct bimodal mechanical response. Such a response has been observed in the case of intergrown polymorphs of aspirin and felodipine. We examine two possible reasons as to why the responses could be for bimodal in this crystal. The first possibility could be that the two domains correspond to regions of the original dihydrate and a lower hydrate that is obtained by the loss of some water. The second possibility could be that these responses correspond to regular and irregular regions in the structure. Nanoindentation is a very useful technique in the characterization of molecular solids, as a complementary technique to X-ray crystallography, because it samples different length scales.