The Magnetic And Transport Properties Of Mn₃Ga Thin Films

Hexagonal DO 19-type Mn3Ga alloys for the hosting of a frustrated Mn-kagome lattice,which gives rise to large anomalous and topological-like Hall effect,making them have potential for antiferromagnetic spintronic devices.Due to the tetragonal DO22-type Mn3Ga with high perpendicular magnetic anisotropy and high spin polarization,can be used in magnetic memory and logic.In this dissertation,Mn3Ga alloy thin films are the main research object,the magnetic properties and transport properties of MnmGa thin films with different phase structures are measured.The experimental results are explained and analyzed by combining the surface morphology and structure components.According to different growth processes of alloy films this paper divided into two parts:The first part of the work is different growth process of Mn3Ga thin films.The first one is we studied the influences of the deposition temperature to the Mn3Ga films:directly sputtering films on the silicon substrate for high-temperature.Mn3Ga began to form a tetragonal phase at 500℃,it shows obvious tetragonal phase characteristics at 600℃:the magnetization saturation is 350 emu/cc,the coercivity is 0.4 T,and without miscellaneous phase exists.We also studied the effect of annealing temperature on Mn3Ga thin films:The samples were sputtered at room temperature on the Si substrate and then annealed immediately.In this series of samples,coexistence of two phases at 500℃,The sample has a magnetization saturation of 175 emu/cc and a coercivity of less than 100 Oe.When the temperature rises to 600℃,the samples had some problem in surface.The addition of Ta as the buffer layer successfully improves the suitability between the substrate and the sample films,and successfully obtained the tetragonal Mn3Ga.In the second part of the work,we investigated the influence of the type and thickness of the buffer layer on the performance of Mn3Ga thin films.we have achieved to grow Mn3Ga film in both tetragonal and hexagonal phase with a tuned Ta(5 nm)/Ru(x nm)(x = 10,20,30)seed layer on the thermally oxidized Si substrate.Consistent with previous reports,large coercivity and large anomalous Hall resistivity is found in the Ta(5 nm)sample with mixed two phases.With the increasing thickness of Ru,a relatively pure hexagonal phase is obtained,in which the anomalous Hall conductivity nearly vanishes,while an abnormal asymmetric hump structure emerges in the low field region of the Hall resistivity curve.The extracted additional Hall term persists in a large temperature range and presents a signchange at above 200 K.The structure of the hump is caused by the change of magnetic properties.The sign reversal is because the manganese in the hexagonal structure re-spins in the lattice of the pomegranate,which represents the formation of the topological Hall effect.