Magnetocrystalline anisotropy measurements in static or quasistatic magnetic fields

Abstract

Usually the singular point detection (SPD) technique, for measuring magnetocrystalline anisotropies, is easily performed in pulsed fields by direct differentiation of the obtained signal from special pick-up coils. On the other hand the use of static magnetic fields in permitted ranges has many advantages: the field enters completely the sample, there are no eddy current effects present, and there is the possibility of calibration with high precision. The present work analyzes the possibility of applying the SPD technique to static and quasistatic magnetic fields using single or double small modulation fields superimposed. Both amplitude and frequency modulation techniques are analyzed. In case of single amplitude modulations it is possible, from the signal detected by a pick-up surrounding the sample, to derive (d2M/dH2)H=H0 from the amplitude of the component with frequency 2ω and (d3M/dH3)H=H0 from the one with frequency 3ω, H0 being the static magnetic field. As in standard SPD measurements the peaks appearing in further derivatives of the magnetization curves, the order of which depends on the crystal symmetry, correspond to the specimen anisotropy field HA. Pulsed field experimental results are also used to evaluate the amplitude of the obtained signals; they are in the detectable range of available commercial lock-in amplifiers. The double modulation is also analyzed showing that it is very useful in case of large noise problems. The role of frequency modulation is shown as a further improvement of the signal-to-noise ratio. Schematic descriptions of different experimental apparatuses are also given.