Magnetic Properties Across Metal to Insulator Transitions

Room 300, Friday 10th January, 10:30

Magnetic Properties Across Metal to Insulator Transitions

J. de la Venta

Colorado State University

Department of Physics

Controlling the magnetic properties of ferromagnetic (FM) thin films without magnetic fields is an on-going challenge in condensed matter physics with multiple technological implications. External stimuli and proximity effects are the most used methods to control the magnetic properties. An interesting possibility arises when ferromagnets are in proximity to materials that undergo a metal-insulator (MIT) and structural phase transition (SPT).

Canonical examples of materials that undergo MIT and SPT are the vanadium oxides (VO₂ and V₂O₃). VO₂ undergoes a metal/rutile to an insulator/monoclinic phase transition at 340 K. In V₂O₃ the transition at 160 K is from a metallic/rhombohedral to an insulating/ monoclinic phase. We have investigated the magnetic properties of different combinations of ferromagnetic metals and vanadium oxide thin films.

In a first example I will show that the stress and phase separation associated with the structural transition produce large changes in the magnetic properties of films in the proximity of the oxides. In a second example I will show that the creation of a Fe₃O₄ interface in Permalloy (Ni₈₀Fe₂₀) / V₂O₃ bilayers gives rise to exchange bias and a vertical shift in the magnetization. Both effects are due to the change in the easy axis of the magnetization across the Fe₃O₄ Verwey transition.