Spin and charge transport in ferromagnet-superconductor-ferromagnet heterostructures: Stoner versus spin mass mismatch mechanism

TL;DR

This paper compares charge and spin transport in ferromagnet-superconductor-ferromagnet heterostructures driven by Stoner versus spin mass mismatch mechanisms, revealing distinct conductance behaviors useful for probing ferromagnetic order origins.

Contribution

It introduces a comparative analysis of transport phenomena in F/S/F junctions for Stoner and spin mass mismatch ferromagnets, highlighting their different conductance responses.

Findings

Large mass mismatch enhances low-bias conductance in SMM F/S/F junctions.

Spin transport exhibits opposite bias response in SMM compared to Stoner ferromagnets.

Superconductivity significantly amplifies conductance at the gap edge.

Abstract

We study transport phenomena through a ballistic ferromagnet-superconductor-ferromagnet (F/S/F) junction, comparing the case in which the ferromagnetic order in the two F layers is of the standard Stoner type with the case where it is driven by a spin mass mismatch (SMM). It is shown that the two mechanisms lead to a different behavior in the charge and the spin conductances, especially when compared to the corresponding non-superconducting ferromagnet-normal-ferromagnet (F/N/F) junctions. In particular, when the injected current is perpendicular to the barrier, for high barrier transparency and large magnetization of the F layers, the large mass mismatch gives rise to an enhancement of both low-bias charge and spin conductances of the F/S/F junction, which is not observed in the equal-mass case. When all the allowed injection directions are considered, the low bias enhancement of the charge conductance for SMM leads still holds for high barrier transparency and large magnetization of the F layers. However, in the case of non-transparent interfaces, spin transport with SMM ferromagnets exhibits an opposite sign response with respect to the Stoner case at high biases for all magnetization values, also manifesting a significant amplification induced by superconductivity at the gap edge. The above mentioned differences can be exploited to probe the nature of the electronic mechanism underlying the establishment of the ferromagnetic order in a given material.