Research On Magnetoresistance Of Metal Films

Magnetoresistance effect refers to the effect that the resistance of a material changes with the change of the external magnetic field.It is one of the important means to study the transport properties of materials,and it is widely used in magnetic sensors,magnetic storage and other fields.At present,the researches on magnetoresistance are mainly focused on the two fields of giant magnetoresistance in non-magnetic materials and angular magnetoresistance in magnetic materials.By changing the temperature,magnetic field and other conditions,the change law and physical nature of magnetoresistance are studied.In this work,we studied the magnetoresistance of non-magnetic metal Al,ferromagnetic single crystal Co and ferrimagnetic Co₆₅Tb₃₅ films.Combined with Hall and other characterization methods,we made detailed analysis and demonstration,and obtained the following innovative results:1.Large magnetoresistance phenomenon in Al/SrTiO₃ heterostructures.As the temperature decreases and the magnetic field increases,the magnetoresistance increases gradually,and the magnetoresistance reaches 410%at 5 K and 9 T.At the same time,hall resistance is nonlinear and meets the Two-carriers model.By fitting the concentration and mobility of electron and hole,it is proved that the large magnetoresistance originates from the compensation mechanism of electron and hole.Moreover,the angle-dependent magnetoresistance of the system with two carriers is further studied.Different from the single carrier,the peaks and valleys of the curves are obviously asymmetric,and it is caused from the different deviation of the current trajectory caused by the electrons and holes.2.Anomalous anisotropic magnetoresistance in single crystal Co/SrTiO₃heterostructures.The anisotropic magnetoresistance of Co[100]and Co[110]crystal direction were measured under different temperature,and it was found that when the temperature was less than 100 K in Co[100]crystal direction,the longitudinal magnetoresistance gradually became negative,while the transverse magnetoresistance was always positive.However,for Co[110]crystal direction,the longitudinal magnetoresistance was always positive and the transverse magnetoresistance became negative when the temperature was less than 100 K.In addition,the amplitude ratio of Co[110]to Co[100]crystal direction is as high as 29 times at 100 K.The phenomenological analysis method based on crystal symmetry expansion can explain our experimental results well,and it is found that the anisotropic magnetoresistance of this anomaly is caused by the competition between the crystal-independent magnetoresistance term and the crystal-related magnetoresistance term.3.Temperature-dependent angular magnetoresistance in ferromagnetic Co₆₅Tb₃₅films.It is found that the transition point of Hall effect corresponds to the compensation point of magnetic temperature 170 K,and the sign of angular magnetoresistance changes from positive to negative to positive,and the magnitude is approximately zero at 200 K and 140 K.By the measurement of changing magnetic field and theoretical analysis,it is proved that the complex variations of magnetoresistance with temperature are the result of the competition between the anisotropic magnetoresistance away from the compensation point and the ordinary magnetoresistance near the compensation point.It is proved that magnetoresistance is both related to transition metals and rare earth metals and is not zero at the magnetic compensation point.