Fabrication And Transport Properties Of Magnetic Oxide Fe₃O₄ And Topological Semimetal ZrSiS

In recent decades,the rapid development of information science has increasingly demands for electronic materials and devices as humans stepping into the era of electronic information.Faster,lower energy consumption and higher storage density are the new demands for electronic science.Electronic materials are the key part of devices.The materials and devices can't satisfy the need of human with only considering the charge nature due to the constraint of quantum effect and Moore law.Therefore,magnetic oxides considering spin nature,their composite structures,and novel electronic materials such as topological semimetal become hot research fields.Magnetic oxide Fe3O4 and its composite structures representing traditional electronic materials and topological semimetal ZrSiS series representing novel electronic materials are selected as our research materials.Fe3O4 is the excellent spin injection source in spintronics due to its theoretical 100%polarization at Fermi level and high Curie temperature(858 K).Topological semimetal ZrSiS series,which rising in the last two years,will have promising future in application of electronic devices,because of their special band structure,novel transport behaviors and potential spin injection source due to spin-momentum locking on topological surface.In my two research materials,Fe3O4 is traditional and classic while ZrSiS is novel and fashion,which make our work unconfined,no bias and let the author step into the research road deeply and comprehensively.Research results can be summarized as the following three parts.(1)Quasi-two-dimensional Fe3O4 epitaxial thin films have been synthesized by pulsed laser deposition technique at various oxygen pressures.The saturation magnetization of the Fe3O4 films are found to decrease from 425 emu/cm3 to 175 emu/cm3 as the growth atmospheres varying from high vacuum(?1×10-8 mbar)to oxygen pressure of 1×10-3 mbar.The ratio of Fe3+/Fe2+ increases from 2 to 2.7 as oxygen pressure increasing evidenced by fitting X-ray photoelectron spectroscopy,which weakens the net magnetic moment generated by Fe2+ at octahedral sites as the spins of the Fe3+ ions at octahedral and tetrahedral sites are aligned in antiparallel.(2)Fe3O4 nanoparticles decorated on the graphene surface can dramatically modify the Schottky barriers of Fe3O4/graphene devices possibly due to the magnetic stray field from the Fe3O4 noparticles in proximity to the graphene.The alignment mechanism of spin in antiphase domain boundaries(APBs)of Fe3O4/YIG is studied by transport properties firstly.By contrast Fe3O4/YIG with different thickness of Fe3O4 or YIG layer,the resistance of structure with thicker YIG layer is smaller than that with thinner YIG layer and the magnetoresistance(MR)of Fe3O4/YIG structure with thicker YIG layer is larger than that of thinner YIG layer.This phenomenon is explained by polarization and realignment of spin in APBs due to the magnetic YIG layer.(3)ZrSiS single crystals are fabricated by chemical vapor transport method.Two SdH oscillations with different frequency are investigated by transport measurement,in which one is corresponding with trivial and another is corresponding with nontrivial Berry phase.They come from two of the four Dirac cone at Fermi level.Cyclotron mass,mobility and other significant physic parameters are fitted by LK equation.The mobilities from both SdH oscillations are larger than 5 000 ccm2V-1s-1.The direct quantum transport evidence of the 3 dimensional nodal-line semimetal phase of ZrSiS is investigated by angular-dependent MR both in ac and be planes.Fitted with two-carrier model,the MR yields a high nodal-line fermion density of 6×1021 cm 3 and a perfect electron/hole density ratio of 0.94,which is corresponding with semiclassical expression fitting of Hall conductance Gxy and theoretical calculation.The beautiful butterfly shaped MR are investigated both in ac and be planes.The more excellent transport properties of ZrSiS in high pulsed field up to 60 T are studied and MR of 200 000%is investigated.The splitting of Landau level at above 20 T and blow 10 K is induced by the Zeeman effect and orbital contribution.Stronger and more sensitive de Haas-van Alphen(dHvA)quantum oscillations are investigated based on TORQUE technique.Cyclotron mass,mobility and other significant physic parameters are analyzed with dHvA oscillations.They are all corresponding with the parameters from SdH oscillations.