Vortex-like state observed in ferromagnetic contacts

TL;DR

This paper reports the observation of a vortex-like spin state in ferromagnetic point-contacts, revealing complex magnetic configurations and weak surface coupling through three-level resistance states.

Contribution

It introduces the detection of a spin-vortex state in nanoscale ferromagnetic contacts, expanding understanding of magnetic states in such systems.

Findings

Observation of a third intermediate-resistance state in point-contacts

Interpretation of this state as a spin-vortex nucleated by Oersted field or geometry

Evidence of weak coupling of interface spins to bulk spins

Abstract

Point-contacts (PC) offer a simple way to create high current densities, 10^9 A/cm^2 and beyond, without substantial Joule heating. We have shown recently (Nano Letters, 7 (2007) 927) that conductivity of nanosized PCs between a normal and ferromagnetic metals exhibits bi-stable hysteretic states versus both bias current and external magnetic field - the effect typical for spin-valve structures. Here we report that apart from the bi-stable state a third intermediate-resistance state is occasionally observed. We interpret this state as due to a spin-vortex in the PC, nucleated either by Oersted field of the bias current and/or by the circular geometry of PC. The observed three-level-states in the PC conductivity testify that the interface spins are both weakly coupled to the spins in the bulk and have depressed exchange interaction within the surface layer.