Evidence for Ferromagnetic Clusters in the Colossal-Magnetoresistance Material EuB6

Abstract

We combined scanning tunneling microscopy and locally resolved magnetic stray field measurements on the ferromagnetic semimetal EuB_{6}, which exhibits a complex ferromagnetic order and a colossal magnetoresistance effect. In a zero magnetic field, scanning tunneling spectroscopy visualizes the existence of local inhomogeneities in the electronic density of states, which we interpret as the localization of charge carriers due to the formation of magnetic polarons. Micro-Hall magnetometry measurements of the total stray field emanating from the end of a rectangular-shaped platelike sample reveals evidence for magnetic clusters also in finite magnetic fields. In contrast, the signal detected below the faces of the magnetized sample measures a local stray field indicating the formation of pronounced magnetic inhomogeneities consistent with large clusters of percolated magnetic polarons.

Control of Mooij correlations at the nanoscale in the disordered metallic Ta–nanoisland FeNi multilayers

“…Here electronic correlations inevitably existing between localised electrons [25][26][27][28] may develop when metallic charge carriers become self-localised in the metallic magnetic clusters near the large localised moments of Tb 4f states. This is also supported by the recent evidence of the formation of intrinsic inhomogeneous states represented by ferromagnetic clusters (called magnetic polarons) in magnetic materials, in which the electronic and magnetic properties are strongly modified by the exchange coupling between the conduction electrons and local magnetic moments 29 .…”

A new view on the origin of zero-bias anomalies of Co atoms atop noble metal surfaces

“…ignatures of many-body phenomena in solid state physics are diverse [1][2][3][4][5] . One of them is the Kondo effect emerging from the interaction between the sea of electrons in a metal and the magnetic moment of an atom 6,7 , whose signature is expected below a characteristic Kondo temperature T K .…”

Towards a Single Chemical Model for Understanding Lanthanide Hexaborides

“…6 Lanthanide hexaborides (LnB6) are quantum materials that show a number of anomalous and seemingly contradictory features, in spite of having the same crystal structure (CaB6-type, space group, see Figure 1A). [7][8][9][10][11][12] For example, both EuB6 and SmB6 have an anomalous behavior in the specific heat as a function of temperature, T (the so-called Schottky anomaly). 13,14 Many electronic properties of SmB6 and EuB6, such as resistivity and electronic transport, are highly sensitive to T and pressure, p. 15,16 However, some other properties of these two alloys are very different: SmB6 is Sm(II)/Sm(III) mixed-valent, whereas EuB6 is not.…”