Magnetism and structure of magnetic multilayers based on the fully spin polarized Heusler alloys Co2MnGe and Co2MnSn

TL;DR

This study investigates the magnetic and structural properties of multilayers based on fully spin-polarized Heusler alloys Co2MnGe and Co2MnSn, revealing critical thickness effects and unique magnetic phenomena at interfaces.

Contribution

It provides new experimental insights into the magnetic ordering and interface effects in Heusler alloy multilayers with different interlayers, using a comprehensive set of measurement techniques.

Findings

Loss of ferromagnetic order below 1.5 nm thickness

Spin glass order replaces ferromagnetism in very thin layers

Exchange bias observed in Co2MnGe/Au multilayers

Abstract

Our Introduction starts with a short general review of the magnetic and structural properties of the Heusler compounds which are under discussion in this book. Then, more specifically, we come to the discussion of our experimental results on multilayers composed of the Heusler alloys Co2MnGe and Co2MnSn with V or Au as interlayers. The experimental methods we apply combine magnetization and magneto-resistivity measurements, x-ray diffraction and reflectivity, soft x-ray magnetic circular dichroism and spin polarized neutron reflectivity. We find that below a critical thickness of the Heusler layers at typically dcr = 1.5 nm the ferromagnetic order is lost and spin glass order occurs instead. For very thin ferromagnetic Heusler layers there are peculiarities in the magnetic order which are unusual when compared to conventional ferromagnetic transition metal multilayer systems. In [Co2MnGe/Au] multilayers there is an exchange bias shift at the ferromagnetic hysteresis loops at low temperatures caused by spin glass ordering at the interface. In [Co2MnGe/V] multilayers we observe an antiferromagnetic interlayer long range ordering below a well defined Neel temperature originating from the dipolar stray fields at the magnetically rough Heusler layer interfaces.