Electric field control of magnetic tunnel junctions in multiferroic heterostructures

With the rapid development of advanced information technology, the requirement for high-performance memory with high storage density, fast reading and writing, and low energy consumption is increasing. Magnetic tunnel junctions (MTJs) possessing a large tunnel magnetoresistance ratio at room temperature, are the core elements of magnetic sensors, magnetic reading heads, magnetic random-access memory (MRAM), and so on. Currently, the mainstream writing operation of the MTJs is based on electric current, and it can be significantly reduced if an electric field is used instead. Therefore, it is important to modulate the reversible and nonvolatile resistance states of MTJs via electric fields. However, the approaches of changing the insulator layer of the MTJ into a ferroelectric material or voltage-controlled magnetic anisotropy have some problems, such as low operating temperature, magnetic field assistance, and volatile modulation. The study of the electric field control of magnetism based on strain in ferromagnetic/ferroelectric multiferroic heterostructures provides a new approach for the electric field to modulate the resistance states of the MTJs. In this review paper, the progress of electric field control of resistance states of MTJs in Pb(Mg1/3Nb2/3)0.7Ti0.3O3-based multiferroic heterostructures is briefly introduced. In the first part, the importance of MRAM and electric field control of resistance states of MTJs is introduced. In the second part, we discuss the electric field control of resistance states of in-plane MTJs. The relative angle between the free and reference layers can be modulated to 90° and 180°. The dipole interaction between the free layer and the reference layer can be used to achieve nonvolatile electric-field control of the MTJs’ resistances via volatile strain. In the third part, we discuss the electric field control of the resistance states of p-MTJs. A method for realizing electric field control nonvolatile and reversible high and low resistance states in p-MTJs under zero magnetic field is introduced. Finally, a further outlook on the electric field control of the resistance states of MTJs in multiferroic heterostructures is presented.