Theoretical study of the interaction between a magnetic nanotip and a magnetic surface.

Abstract

A theoretical study of the electronic structure of transition-metals' magnetic nanotips and of the interaction of such tips with magnetic surfaces is performed within the tight-binding scheme. The real-space recursion method is used to calculate the local densities of states of the interacting tips and surfaces. We consider more especially Fe supported tips and both Cr and Ni magnetic surfaces. A strong enhancement of the magnetic moments is observed on the tip's surfaces and tip's apex atoms. The interaction of such tips with Cr(001) and Ni(001) surfaces is studied in regime for which the adhesive forces are dominant. Different magnetic tip-sample (TS) configurations are considered. The electronic structure of both the tip and sample are found to be substantially modified due to the TS interaction. These modifications lead to the decrease of the corresponding magnetic moments for decreasing TS distances. The TS interaction energy curves, the magnetic TS coupling energy, and the magnetic ``exchange'' forces are also calculated when the tip's apex is located above high-symmetry surface's sites. Large antiferromagnetic (AP) couplings are found between interacting Fe tip and Cr surface, instead of small ferromagnetic (P) couplings for the Ni surface. According to the values of the magnetic TS ``exchange'' forces and to their variations upon the considered surface's sites, high spatial resolution is expected for such a magnetic force microscopy. Finally, the experimental feasibility for the measurement of such forces and the influence of the tip's morphology on the magnetic contrast are also examined. To our knowledge, this is the first study of the magnetic coupling energy for tip-sample systems.