Magnetotransport Study Of The Spin Torque In Magnetic Heterostructures With Perpendicular Anisotropy

Electrical control over the magnetization of magnetic thin film is one of the most fascinating subjects in spintronics due to its great potential for non-volatile device applications.In this regard,the magnetic herterostructure with perpendicular anisotropy(PMA)is of particular interest in the current-induced magnetization switching.In this thesis,we focus on three perpendicularly magnetized herterostructures comprising MnAl/MgO/MnAl,Pt/Co/MgO and Ta/CoFeB/MgO,to study the perpendicular anisotropy,the impact of spin torques on magnetization switching and possible spin logic applications.The brief is as follows:(1)We perform a first-principle calculation of MnAl/MgO magnetic tunnel junctions on the perpendicular anisotropy and quantum transport properties.It's shown that Al-terminated structure is a better choice for large PMA and Mn-O bond in the interface is detrimental for the PMA.Giant tunneling magnetoresistance ratios are predicted in both terminated structures and it can be maintained under large bias in Mnterminated structure.The in-plane spin-transfer torque increases linearly with applied voltage due to the large net spin current.(2)In the frame of macrospin,we deduce the equations satisfied by the stable states of magnetic moment at the presence of spin torques.By the discussion of a special case,we elaborate the importance of the in-plane magnetic field in deterministic switching.Meanwhile,we give the criterion of stability for the stable states of magnetic moment.(3)By optimizing the experimental conditions,we obtain the Pt/Co/MgO and Ta/CoFeB/MgO stacks with PMA.The effective field of current in both stacks are characterized by lock-in technique.With the aid of bias current,we study the different influences of field-like and damping-like toque on magnetization switching and the main features of results can be qualitatively reproduced by the macrospin model.(4)Based on the cross-shaped Hall bar structure,we experimentally demonstrate two kind of spin logic cells utilizing Pt/Co/MgO stacks.For the first demonstration,two logic input currents are applied to the same channel of Hall bar and the in-plane magnetic field is along this channel.As for the second demonstration,two logic input currents are separately applied to two mutual orthogonal channels and the in-plane magnetic field is along angle bisector between two currents.In both demonstrations,five logic functions are all realized in a single cell and the logic cell can be easily program and reprogram into desired logic function and the data stored in the cell is nonvolatile.