PhD Dissertation: Voltage-controlled effects in Magnetic Tunnel Junctions

Meng Xu, University of Arizona

When

1:30 – 2:30 p.m., April 30, 2020

Where

Abstract: 

Magnetic tunnel junction (MTJ), which features a core structure of ferromagnet/oxide/ferromagnet, serves as one of the building blocks in the study of spintronics. It can store information in a nonvolatile manner and is compatible with the standard semiconductor process. With the everincreasing demand for data processing power, the efficient reading/writing in MTJ is vital for the development of spintronics memory to replace conventional transistor memories. The voltage-controlled effects are naturally energy saving in a resistive system like MTJ. In this dissertation, we focus on the model system of CoFeB/MgO/CoFeB MTJ. First, we will introduce an unconventional procedure to fabricate high-quality MTJ nanopillars, which are essential for the study of spin dynamics under the influence of voltage. Then, we will demonstrate sub-nanosecond magnetic switching in MTJ nanopillars by voltage-controlled magnetic anisotropy (VCMA) effect. Some fascinating phenomena which only exist in this short time scale are observed. With the help of interfacial engineering and increased range of annealing by structural modification, the VCMA coefficient can be significantly enhanced and we obtained the lowest switching energy ever reported. In the third part, a novel voltage-controlled exchange bias (VCEB) effect is reported and its implication on magnetic switching and further enhancement of TMR is discussed.

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