Inter-grain tunneling in the half-metallic double-perovskites Sr$_2$BB'O$_6$ (BB'-- FeMo, FeRe, CrMo, CrW, CrRe

TL;DR

This study investigates inter-grain tunneling in Sr$_2$BB'O$_6$ double-perovskites, revealing a consistent tunneling barrier and a linear relationship between tunneling properties and magnetic moment across various samples.

Contribution

It demonstrates the universal presence of an intrinsic insulating boundary layer and links tunneling behavior to magnetic properties in these materials.

Findings

Tunneling constant is approximately 2 for all Sr$_2$FeMoO$_6$ samples.

The tunneling constant decreases linearly with increasing magnetic moment.

Inter-grain transport is well described by the fluctuation induced tunneling model.

Abstract

The zero-field conductivities ($\sigma$) of the polycrystaline title materials, are governed by inter-grain transport. In the majority of cases their $\sigma$(T) can be described by the "fluctuation induced tunneling" model. Analysis of the results in terms of this model reveals two remarkable features: 1. For \emph{all} Sr$_2$FeMoO$_6$ samples of various microstructures, the tunneling constant (barrier width $\times$ inverse decay-length of the wave-function) is $\sim$ 2, indicating the existence of an intrinsic insulating boundary layer with a well defined electronic (and magnetic) structure. 2. The tunneling constant for \emph{all} cold-pressed samples decreases linearly with increasing magnetic-moment/formula-unit.