Electric-field-mediated Electrical Transport And Magnetic Properties Of PMN-PT Based Heterostructures

Studying electric-field-mediated electrical transport and magnetic properties of materials,not only benefits to understanding the fundamental physical properties but also has huge potential applications in energy and environment.In this work,the Pb(Mg_1/3Nb_2/3)_0.7Ti_0.3O₃（PMN-PT）based heterostructures were fabricated by magnetron sputtering,including Co₃O₄/PMN-PT,Co Fe₂O₄/La_0.67Sr_0.33Mn O₃/PMN-PT（CFO/LSMO/PMN-PT）and LSMO/PMN-PT heterostructures.The electric-field-modulated electrical transport and magnetic properties were studied systematically.Electric-field-modulated electrical transport properties of Co₃O₄/PMN-PT heterostructure were achieved.The Co₃O₄/Mg Al₂O₄（MAO）and Fe₃O₄/Co₃O₄/MAO heterostructures were first fabricated to investigate the magnetic and photocurrent properties of Co₃O₄ films.The Fe₃O₄/Co₃O₄/MAO heterostructure presents large exchange bias,which derives from the interfacial coupling between the antiferromagnetic Co₃O₄ and ferromagnetic Co_xFe₃-_xO₄ layer formed through the interdiffusion.Based on the strong optical absorption properties of the Co₃O₄ film,the enhanced current of～79%is achieved in the Fe₃O₄/Co₃O₄ heterostructure under the irradiation of 405-nm laser.Compared to the Co₃O₄/MAO and Co₃O₄/Sr Ti O₃heterostructures,the Co₃O₄/PMN-PT heterostructure shows dislocation defects and owns a higher concentration of Co vacancies,which derive from the ferroelectric-domain-shape surface morphology and phase transition of the PMN-PT substrates.The Co vacancies reduce the resistivity of Co₃O₄/PMN-PT heterostructure by 2～3 orders of magnitude.The results of first-principles calculations indicate that Co vacancies can build impurity levels near the Fermi level of Co₃O₄,which are beneficial to forming free-moving holes in the valence band.The free-moving holes can also be accumulated/dissipated by the ferroelectric field effect of the PMN-PT substrates,leading to upward/downward bending of conduction and valence bands,and further low/high resistance states.Electric-field-mediated magnetic properties were also investigated in the CFO/LSMO/PMN-PT heterostructure.The butterfly-like electric-field-dependent magnetization indicates that the strain effect plays a critical role in the electric-field-mediated magnetic properties,causing the magnetization to decrease along the[01-1]direction but increase along the[100]direction in the CFO/LSMO/PMN-PT heterostructure.Due to the large magnetostriction of the CFO layer,the coercivity of the CFO/LSMO/PMN-PT heterostructures decreases～50%along the[01-1]direction under the electric fields.The significant modulation of the coercivity makes it feasible to achieve the electric-field-controlled magnetoresistance in the metal/CFO/LSMO/PMN-PT spin filter magnetic tunneling junctions.To further explore and distinguish the mechanism of electric-field modulation,the LSMO/PMN-PT（011）and（001）heterostructures were fabricated.Their electric-field-dependent resistance exhibits asymmetric-butterfly shape under bipolar electric fields,indicating the existence of volatile strain and non-volatile ferroelectric field effects.By applying unipolar electric fields,the LSMO/PMN-PT（011）heterostructure presents obvious non-volatile strain effect compared to the LSMO/PMN-PT（001）heterostructure,which is due to the in-plane polarization of the PMN-PT（011）substrates.The volatile strain,non-volatile strain,and ferroelectric field effects can enhance or weaken the double-exchange coupling of the LSMO films,achieving the modulation of resistance.