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
Abstract
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.ɛxx -ɛyy ≈ - 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.
- Publication:
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Journal of Magnetism and Magnetic Materials
- Pub Date:
- April 2018
- DOI:
- 10.1016/j.jmmm.2017.11.082
- Bibcode:
- 2018JMMM..451..420B
- Keywords:
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- Vibrating sample magnetometer;
- Synchronous noise;
- Mechanical resonator;
- Ni thin film;
- Anisotropic spin-polarization;
- Strain-induced uniaxial magnetic anisotropy