The Study Of Anomalous Nernst Effect In Iron-based Magnetic Films

In recent years,electronic comp onents continue to be miniaturized,and their integration and operation speed are also increasing.However,the local high tem.perature of the device seriously reduces the operation speed and service life of the electronic components.Therefore,reasonable absorption and utilization of the waste heat from devices has become the key to the development of green information technology with high efficiency and low power consumption.Anomalous Nernst effect(ANE)of ferromagnetic materials has attracted much attention due to its ability to convert thermal energy to electrical energy.At present,the research on ANE of ferromagnetic material main ly focuses on the structural design.However,the anomalous Nernst effect of ferromagnetic layer itself plays an important role in the overall effect of devices.Therefore,in order to improve the thermoelectric conversion efficiency per unit magnetic moment of thermoelectric devices based on anomalous Nernst effect,exploring the physical mechanism of anomalous Nernst effect from the intrinsic factors of ferromagnetic materials and increasing anomalous Nernst effect not only have theoretical significance but also has important application,value.The existing theoretical studies have shown that the anomalous Nernst effect is closely related to the spin-orbit coupling energy(SOC)and the position of Fermi surface.Based on this,the research of this paper is divided into the following three directions:1.The Feo.5(PtxPd1-x)0.5(FePtPd)(0≤x≤1)ternary alloy films with different compositions were selected as the research object.By changing the content of Pt and Pd in FePtPd alloy,the spin orbit coupling energy of the system was continuously and singly regulated,so as to study the influence mechanism of spin-orbit coupling energy on anomalous Nernst effect.FePtPd ternary alloy films with thickness of 20±2 nm were prepared on quartz glass substrates by DC maegnetron sputtering.The samples were all fcc structure.By measuring the ANE of samples with different compositions,it was found that the anomalous Nernst voltage VANE increases with the heating current I applied to the heat source increasing,while it shows a linearly increasing dependence with the heating power P.It was also found that the anomalous Nernst efficiency vN increases with the increase of the proportion of Pt atoms,which is due to the enhancement of SOC.This part comprehensively gives the regulation and mechanism of SOC to ANE,which will be helpful to the research and development of next-generation spintronics and thermoelectric devices.2.The FeXNi1-x(FeNi)(x=0-0.55,1)epitaxial alloy films with different compositions were selected as the research object.By changing the compositions of FeNi alloy,the position of Fermi surface of the system was continuously and singly regulated to study its influence mechanism on anomalous Nernst effect.FeNi epitaxial films with thickness of 40±3 nm were prepared on single crystal MgO(001)substrates by DC magnetron sputtering.The ANE of the samples with different compositions was measured,and it was found that the value of the anomalous Nernst voltage VANE increases with the increase of the heating current I applied to the heat source,while it increases linearly with the increase of heating power P.For fee FexNi1-x(x=0-0.55)film samples,VANE and anomalous Nernst efficiency vN increase with the increase of the Fe content x.The theoretical calculation shows that with the replacement of Ni by Fe atom,the Fermi level will increase and thus affecting the value of the VANE and vN.Compared with fee FeNi alloy,the VANE and vN of bcc Fe epitaxial film decrease sharply and change sign,which is resulted from the change of intrinsic mechanisms contribution caused by the band filling effect.Therefore,this part of the work profoundly reveals the microscopic mechanism of ANE in the FeNi epitaxial system,which will provide new ideas for regulating and increasing the anomalous Nernst ffect.3.The disordered(FexNi1-x)0.5Pt0.5(0≤x≤1)ternary alloy system was chosen.On the one hand,compared with the conclusion of FexNi1-x system,it was found that SOC of the system increased with the doping of heavy metal Pt,and therefore the ANE was also enhanced.On the other hand,the Fermi surface position of the system is tuned by changing the relative atomic content of Fe and Ni.It is concluded that with the increase of Fe atoms,the Fermi surface position increases,and both VANE and vN increase.