Date of this Version
Echtenkamp, W. (2021). Voltage-Controlled Magnetization in Chromia-based Magnetic Heterostructures [Doctoral Dissertation, University of Nebraska-Lincoln]
Spintronics promises a new generation of low-power, high-speed, non-volatile memory and logic devices. Heterostructures based on magnetoelectric chromia enable the direct manipulation of magnetization by applied electric fields and emerged as a promising building block for spintronic devices. In this dissertation, several interesting emergent magnetic properties arising in these device-enabling building blocks are examined. In some cases, exchange coupling at the interface between the magnetoelectric antiferromagnet and an adjacent ferromagnet stabilizes the interfacial antiferromagnetic domain state against the electrically induced rotation of the bulk spin structure. Upon magnetically cycling the ferromagnet, the magnetoelectric antiferromagnet relaxes towards a commensurate spin structure between bulk and interface. This relaxation is reflected in the electrically controllable exchange bias training effect of the ferromagnetic hysteresis loop. In other cases, the interfacial exchange locks the antiferromagnetic interface to rotate along with the ferromagnet. This causes a competition between the exchange energy at the interface and the anisotropy energy of the crystal. At the crossover point between these two mechanisms there occurs a simultaneous disappearance of exchange bias with a more than twofold increase in coercivity of the ferromagnetic hysteresis loop. Finally, it is shown that by boron doping, the Néel temperature of chromia can be controllably tuned from the undoped temperature of 307 K, up to at least 400 K. In addition, boron doped chromia exhibits voltage-controlled and non-volatile Néel vector reorientation in the absence of an applied magnetic field, further expanding its functionality and revealing B-doped chromia is an ideal material for voltage-controlled antiferromagnetic spintronics.
Advisor: Christian Binek