Diamagnetic to ferromagnetic switching in VO2 epitaxial thin films by nanosecond excimer laser treatment

Abstract

VO2(010)/NiO(111) epitaxial heterostructures were integrated with Si(100) substrates using a cubic yttria-stabilized zirconia (c-YSZ) buffer. The epitaxial alignment across the interfaces was determined to be VO2(010)‖NiO(111)‖c-YSZ(001)‖Si(001) and VO2[100]‖NiO⟨110⟩‖c-YSZ⟨100⟩‖Si⟨100⟩. The samples were subsequently treated by a single shot of a nanosecond KrF excimer laser. Pristine as-deposited film showed diamagnetic behavior, while laser annealed sample exhibited ferromagnetic behavior. The population of majority charge carriers (e−) and electrical conductivity increased by about two orders of magnitude following laser annealing. These observations are attributed to the introduction of oxygen vacancies into the VO2 thin films and the formation of V3+ defects.

Multifunctional heterostructures integrated on Si (100)

“…MgO and TiN were found to be non-magnetic. The fact that the XRD and XPS data did not reveal any indication of secondary impurities, before or after laser annealing, coupled with the observation of no FE features after laser irradiation, leads us to believe that oxygen vacancies 34,35,[66][67][68]78,79 (cause leakage currents, adversely affecting ferroelectricity) are responsible for the observed FM features. This finding is similar to many other reports.…”

“…Doping of (Mn 76 and Nb 77 ) STO crystal and thin films has been shown to be one means of inducing ferromagnetism. In addition, recent studies here at North Carolina State University [66][67][68] suggest that laser irradiation/annealing processes offer an alternative approach for introducing magnetism. Similarly, the irradiation-or defect-induced ferromagnetism has been widely reported in a variety of solids.…”

“…[65][66][67][68][69][70][71] It was suggested that the combination of magnetic defects arising from various defects such as vacancies, interstitials, deformation and partial destruction of the lattice structure may explain the onset of magnetic order. This represents an alternative approach to introducing magnetic moments into the multifunctional heterostructures considered in this study.…”

Band filling dependence of the Curie temperature in CrO2

“…Nevertheless, both HF calculations and DMFT support strong FM character of exchange interactions in VO 2 , if they are calculated near the FM state. It is also important to note that the electronic structure and exchange interactions in VO 2 exhibit the strong dependence on the magnetic state in which they are calculated (and in this sense, VO 2 can be regarded as a smart material [26,27]). For instance, in the HF calculations, the AFM alignment of two V spins in the primitive cell opens the band gap (of about 0.1 eV) and changes the character of NN interactions to the AFM one (J 1 = −14.6 meV).…”

“…Such a possibility for VO 2 was indeed demonstrated in refs. [26,27], where it was argued that by deposing VO 2 on different substrates one can achieve the room-temperature ferromagnetism, which can be switched 'on' and 'off', depending on the treatment conditions. This behavior was attributed to the V 3+ defects, existing in the thin films of VO 2 .…”