Exchange coupled Mn2Au/Ni81Fe19 heterostructures for antiferromagnetic spintronics

Abstract

The last few years have witnessed an emerging interest in building spin-electronics devices for memory and logic applications from antiferromagnets due to their highly favourable properties of external field stability, ultrafast magnetization dynamics etc. However, unless antiferromagnets are manipulated electrically, they cannot be effectively implemented in practical microelectronic devices that rival existing technologies, let alone supersede them. One of the proposed ideas is to use antiferromagnets with a special crystallographic symmetry (as found in Mn2Au & CuMnAs) in memory bit cells. Theoretically, their unique structure enables their bi-stable magnetic order to be reversibly manipulated by short electrical pulses. This so called ‘Néel spin-orbit torque’ based switching of such antiferromagnets might require current densities comparable to values typically needed for the traditional spin-torque switching of ferromagnets. Though promising strides towards experimental proof were made in recent years, yet another challenge impeding the practicality of antiferromagnets remains to be tackled. Currently, the state of the antiferromagnet (upon reorientation of its magnetic order) is read via anisotropic magnetoresistance which is usually a tiny change of less than 1% in the resistance of the structure. However, the integration of a memory element into a functional CMOS circuit with a high signal to noise ratio (for good scalability) demands a significantly larger electrical readout. This work explores the growth of high quality epitaxial Mn2Au (001) thin films and the exceptionally robust interfacial exchange coupling found in the Mn2Au/Ni81Fe19 system. Such strongly coupled antiferromagnet/ferromagnet bilayers open up the possibility of generating large magnetoresistance effects via the ferromagnet for electrical readout while retaining the core advantages offered by the antiferromagnet. Furthermore, imprinting of the antiferromagnetic domain pattern on the ferromagnet facilitates its visualization via well established imaging techniques for ferromagnets. Additionally, it enables an in-house study of current induced switching of antiferromagnets while eliminating the need for synchrotron based microscopy. Thus, this research will help make antiferromagnets more accessible by addressing some of the key issues identified in the quest for next generation spintronics devices based on these remarkable materials.