Electric-field Control Of Magnetization Switching In FM/FE Heterostructures

With the development of information technology, the traditional magnetic random access memory (MRAM) has its inherent advantages, but there are also the inevitable shortcomings, such as low writing speed, high power consumption, low storage density and so on. New storage devices need to be studied to improve the defects of the traditional MRAM. On the basis of the magnetoelectric coupling effect, using the electric field directly control magnetization switching in FM/FE heterostructures can solve these problems.The property of magnetic field induced polarizing reorientation in dielectric is the magnetic-electric (ME) coupling effect, and the converse ME coupling effect means that the magnetic properties can be controlled by the electric field. The converse ME coupling effect has been widely used in the field of spintronics devices. The ME coupling effect was initially found in the single phase multiferroic materials, which both have ferroelectric property and ferromagnetic property. However the single phase multiferroic materials with both of room temperature ferroelectric and ferromagnetic properties are rare and the ME coupling effect is too small to be used. Then the artificial multiferroic composite materials with strong ME coupling effect were studied as alternatives. Recently the ferromagnetic/ferroelectric (FM/FE) heterostructures called widely attention. In this FM/FE heterostructures using the electric field directly as the writing field can meet the requirements of low-power consumption and miniaturization for information storage devices. This may have potential application in the electric field write/magnetic field read storage devices. There have been many researches studying the electric field controlling magnetic properties in these kinds of FM/FE heterostructures. Among the studies, the strain mediated ME coupling effect is the most used. There ars relatively few researches about strain mediated non-volatile ME coupling, especially the 90° non-volatile magnetization switching, which is critical for the non-volatile FM/FE storage devices. In this work, we study the volatile and the non-volatile magnetization switching by electric field method through converse ME coupling effect. The main results are as follows:(ⅰ) In FeCoSi/PZT actuator heterostructures, the negative voltage can control the magnetization switching, and the positive voltage can tune the magnitude of the anisotropy field, which has potential application in high frequency devices.(ⅱ) In FeNi/Ti/(110)PMN-PT heterostructures, we found that the electric field can realize 90° magnetization switching and adjust the magnitude of the anisotropy field under high electric field region.(ⅲ) In FeCo/Cu/(110)PMN-PT heterostructures, we found two stable magnetization directions were established through a 90° transition of the in-plane uniaxial anisotropy of FeCo film under a positive electric field, and a large nonvolatile remanence ratio tunability between 0.50 and 0.12 was realized using electric field pulses. With the increase of negative electric field, the anisotropy field increases at a rate of around 31.1 Oe/(kV/cm).(ⅳ) to FeCo/Ru/(110)PMN-PT heterostructures, we found the magnetization in the orthogonal directions can be reset by the positive/negative electric fields pulse in PMN-PT/Ru/FeCo heterostructures due to the strain mediated converse magnetoelectric effect. The high (low) resistance state was realized under the negative (positive) electric fields pulse due to the anisotropy magnetoresistance of FeCo films, this may have potential application in the electric field write/magnetic field read storage devices.