Correlation of uniaxial magnetic anisotropy axes and principal resistivities in polycrystalline ferromagnetic films

In the present study, we demonstrate the measurement of resistivity tensor ($ρ$) along the magnetic axes of a polycrystalline film of ferromagnetic permalloy (Py). To this end, conventional Hall-bar and a more recent extended van der Pauw methods were utilized for determining 2D $ρ$ in the film plane. The samples were prepared by normal incidence sputter deposition within an in-situ magnetic field to induce in-plane uniaxial magnetic anisotropy in the film. Since $ρ$ might be affected by the internal magnetization of the film, we performed measurements by rotation of a saturating magnetic field in the film plane. Both methods indicate that the average resistivity is lower along the easy axis of the film compared to the hard axis. Since X-ray diffraction results indicated no dominating texture in the film, we concluded that there is a correlation between uniaxial magnetic axes and principal resistivity axes. This is an important finding that allows determining the direction of magnetic anisotropy axes without magnetometry. The results also verify atomic or pair ordering to be the origin of uniaxial magnetic anisotropy in the Py since resistivity is sensitive to the level of order in solids. The extended van der Pauw utilized here can be easily performed on the as-received samples which is of practical interest.