RESUMO
In this work we investigate the magnetic field dependence of A(g) octahedra rotation (tilt) and B(2g) symmetric stretching modes frequencies at different temperatures. Our field-dependent Raman investigation at 10 K is interpreted by an ionic displacive nature of the magnetically-induced ferroelectric phase transition. The increasing frequency of the A(g) tilt mode with magnetic field gives evidence for the increase of the MnO(6) tilt angle, which in turn leads to a weakening of the ferromagnetic exchange interaction, yielding the necessary conditions for the onset of ferroelectricity on the basis of the inverse Dzyaloshinskii-Moriya interaction. The frequency change of the B(2g) symmetric stretching mode at the ferroelectric phase transition enables one to estimate the shift of oxygen ion positions and the corresponding spontaneous polarization of 480 µC m(-2) in magnitude, which is of the same order as earlier reported values in single crystals.
RESUMO
Magneto-optical Kerr effect (MOKE) magnetometry is an indispensable, reliable, and one of the most widely used techniques for the characterization of nanostructured magnetic materials. Information, such as the magnitude of coercive fields or anisotropy strengths, can be readily obtained from MOKE measurements. We present a description of our state-of-the-art vectorial MOKE magnetometer, being an extremely versatile, accurate, and sensitivity unit with a low cost and comparatively simple setup. The unit includes focusing lenses and an automatized stepper motor stage for angular dependent measurements. The performance of the magnetometer is demonstrated by hysteresis loops of Co thin films displaying uniaxial anisotropy induced on growth, MnIr/CoFe structures exhibiting the so called exchange bias effect, spin valves, and microfabricated flux guides produced by optical lithography.
