Co₂MnSi thin films for spin Seebeck devices and multilayers

The growth and optimisation of Co2MnSi thin films fabricated by PLD have been investigated of application in spin Seebeck Effect (SSE) devices. The results of structural, magnetic and thermal transport measurement of the optimisation of deposition and post-deposition annealing treatments have been presented. In addition, the Co2MnSi films were fabricated as part of SSE devices, [Co2MnSi:Pt]n multilayers, which were fabricated and analysed to investigate the possibility of an enhancement in the thermoelectric signal. The films have been analysed using x-ray diffraction (XRD), x-ray reflectivity (XRR), polarised neutron reflectometry (PNR), magnetometry (SQuID, VSM-SQuID and MOKE) and the contributions from the anomalous Nernst and spin Seebeck effects were analysed on in-house thermal transport equipment. The Co2MnSi films deposited on glass were found to exhibit a development of the atomic site ordering with both deposition and annealing temperature. At an annealing temperature of 300◦C the films grew with a (220) texture and in the B2 phase. At an annealing temperature of 450◦C the films grew with a (220) texture and in the L21 phase. The SSE measurements suggested that bilayers annealed at 300◦C exhibited a larger response than those annealed at 450◦C because the interface quality and width was a more determinant factor in the SSE than the bulk atomic ordering of the film. The multilayers annealed at 450◦C showed absolutely no enhancement from the single bilayer, echoing the need for interface engineering rather than spin generation optimisation. However, the multilayers annealed at 300◦C (with cleaner interfaces) exhibited a thermoelectric enhancement, twice that of the single bilayers.