Spin-dependent thermoelectric effect in Co2Fe0.4Mn0.6Si with perpendicular magnetic anisotropy

We report the anomalous Nernst effect in the half-metallic ferromagnetic Heusler alloy Co2Fe0.4Mn0.6Si in a MgO/CFMS/Pd trilayer stack with perpendicular magnetic anisotropy. We measure a tunable anomalous Nernst effect vary with both the CFMS and Pd thickness to investigate the magnetic proximity effect in Pd layer. The experimental results show that thicker the CFMS in a MgO/CFMS/Pd or the Pd layer is, the larger anomalous Nernst effect signal we can get.

The anomalous Nernst effect (ANE) is a thermoelectric effect which converts thermal energy derives from longitudinal temperature gradiedt along x axis in the ferromagnets into transverse electric signal along y axis,even when there is no external magnetic filed applied along the z axis. It draws much interest for its promising application prospect to harvest electricity from the waste heat by developing power generation devices based on ANE.Extensive efforts on developing this kind of ANE based devices,especially new ANE materials has been made(Schmid 2013)(Sakuraba 2013)(Ramos 2014)(Ando 2016)(Fang 2016).In this paper, we will also make a further investigation about it by performing a systematically ANE measurement on heusler alloy Co2MnFeSi samples with perpendicular magnetic anisotropy. ANE is a transverse thermoelectric effect which generates an electric filed via a spin-orbit interaction in the orthogonal direction between the applied temperature gradient \({\nabla}{T}\) and spontaneous magnetization M in the ferromagnetic material. There have been a few studies on the ANE but the original physical essence has not been clarified so far(Ramos 2014). At the same configuration, the longitudinal spin seebeck effect(LSSE) is always accompanying with the ANE, where the temperature gradient is imposed along the longitudinal direction (Bosu 2011)(Huang 2011)(Meier 2013)(Dejene 2014)(Meier 2015). Based on this, there are some studies focus on separation of the ANE from LSSE (Kikkawa 2013)(Miao 2016).

Recently, the ANE has been investigated in lots of different materials, including Fe3O4 single crystal(Ramos 2014) , the ferromagnetic metal Py (Schmid 2013)(Yin 2013), [Pt/Co]n multilayers(Fang 2016) and so on. However, there are less studies focusing on ANE in half-metallic heusler alloy compound since it is not easy to distinct from SSE. Half-metallic heusler alloy such as Co2MnFeSi have already been regarded as a promising material for the application in spintronics with high curie temperature and large spin polarizations(Sakuraba 2005)(Sakuraba 2006). There are already some work which reported the transport property in current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) in Co2MnSi trilayers (Sakuraba 2010). However, an experimental work directly relating ANE in the heusler alloy material system with high spin polarization is still lacking. As mentioned previously,it is quite challenging to separate the ANE and SSE. There is an ideal solution to avoid the occurrence of SSE with out-of-plane magnetic field and in-plane temperature gradient. In order to realize this idea,some works have been done on perpendicularly magnetized heusler alloy such as Co2MnFeSi/Pd bilayer(Ludbrook 2016)(Ludbrook 2017)[simon].The ANE has already been investigated in non-magnetic metals(NM) connected to ferromagnetic materials(FM) for revealing the magnetic proximity effect(Magnus 2016)(Kim 2016)(Vobornik 2011)(Huang 2012). Here there are pioneering works have revealed a strong relation between ANE and spin orbit coupling(SOC) strength(Fang 2016)(Uchida 2015). However,it is still not clear about the magnetic proximity effect on thermal spin- transport phenomena.There is still the physic origin of it remaining to be revealed.