Spin texture on top of vortex avalanches in Nb/Al_2O_3/Co thin film heterostructures

TL;DR

This study investigates the spin texture formation on top of vortex avalanches in Nb/Al_2O_3/Co heterostructures, revealing stable spin domains associated with dendritic flux penetration that persist at room temperature.

Contribution

It demonstrates the direct imaging and stability of spin textures linked to vortex avalanches in superconductor/ferromagnet heterostructures, a novel observation in this material system.

Findings

Magnetic flux penetrates as dendrites in Nb/Co heterostructures.

Imprinted spin domains are stable at room temperature.

Flux instabilities cause noise in magneto-resistance and Hall measurements.

Abstract

We report on magneto-optical imaging, magnetization, Hall effect and magneto-resistance experiments in Nb/Al_2O_3/Co thin film heterostructures. The magnetic field is applied perpendicularly to the plane of the film and gives rise to abrupt flux penetration of dendritic form. A magnetization texture is imprinted in the Co layer in perfect coincidence with these ramifications. The spin domains that mimic the vortex dendrites are stable upon the field removal. Moreover, the imprinted spin structure remains visible up to room temperature. Complementary magnetization, Hall effect and magneto-resistance experiments were performed in a similar sample where electrical contacts were placed on the Co layer. In the region of the field - temperature diagram where flux instabilities are known to occur in Nb films, irregular jumps are observed in the magnetic hysteresis and large amplitude noise is detected in the magneto-resistance and Hall resistivity data when measured as a function of the field.