Role of sample resistivity in pulsed field anisotropy measurements

The effects of sample resistivity on magnetocrystalline anisotropy field measurements in pulsed fields are studied. Computer programs have been developed for simulating a sinusoidal field penetration and exponential decrease into a long cylindrical sample (one dimension diffusion problem), for the case of linear and nonlinear magnetic field diffusion. Simulations of conducting samples show the dependence of the delay of field at different positions within the sample with respect to the sample resistivity. In magnetic samples the resistivity itself has various effects. The values of the magnetization curve in an increasing field are lower than that corresponding to a decreasing field (this shows a hysteretic behaviour), the magnetic field values are lower in the interior of the sample, the two peaks of the second derivation of the magnetization corresponding to the anisotropy field are shifted, the value of the obtained anisotropy is higher in the increasing field with respect to the decreasing one, while the true anisotropy value lies between those and closer to the peak found in the decreasing field. Experimental results obtained on a Co polycrystalline sample at 78 K are in qualitative agreement with the presented simulations. The optimization of the field rise time in anisotropy field measurements by singular point detection is discussed with respect to the sample resistivity.