High-resolution vector magnetometry: Piezo-spin-polarization effect and in-plane strain-induced dominating uniaxial magnetic anisotropy in a 200-nm-thick Ni thin film

Owing to its high-sensitivity, reliability, fast, versatile and cost-effective operation, vibrating sample magnetometers (VSM) are massively popular characterization instruments at Magnetism laboratories worldwide. Nevertheless, the inherent appearance of synchronous noise represents a major drawback, which critically limits the fine probing of nanometer-sized media. I here report on an innovative approach to eliminate synchronous noise in VSM. This consists of fitting engineered mechanical devices that absorbs vibration energy, dissipating that into heat. Complementarily, a novel transversal pick-up coil system is also presented and analyzed; this detection system has been engineered to enhance the noise-to-signal ratio and optimized for measuring small size thin film samples. The implementation of a combined mechanical and electromagnetic approach enables to notably enhance the VSM performance, achieving a sensitivity better than 1×10-6 emu and a resolution below 5×10-8 emu, so that the magnetization vector in nanostructured media can be accurately mapped out down to cryogenic temperatures. I lastly show precision magnetometry measurements carried out in an epitaxial (0 0 1)-oriented 200 nm-thick Ni thin film. The analysis reveals the arising of an in-plane dominating strain-induced uniaxial magnetic anisotropy, K2ef=-6.455kJ m-3, and a stunning piezo-spin-polarization effect resulting in a remarkable 10% modulation of the magnetization vector, ∼27 emu/cm3, with respect to the cubic lattice axes. Both effects are attributed to the likely existence of an orthorhombic lattice distortion, i.e.εxx-εyy≈-2×10-3. This categorical link enables to assign the observed anisotropic spin-polarization in the Ni overlayer to a two-ion magnetoelastic coupling effect.