A quantum material spintronic resonator

Abstract

In a spintronic resonator a radio-frequency signal excites spin dynamics that can be detected by the spin-diode effect. Such resonators are generally based on ferromagnetic metals and their responses to spin torques. New and richer functionalities can potentially be achieved with quantum materials, specifically with transition metal oxides that have phase transitions that can endow a spintronic resonator with hysteresis and memory. Here we present the spin torque ferromagnetic resonance characteristics of a hybrid metal-insulator-transition oxide/ ferromagnetic metal nanoconstriction. Our samples incorporate $${\mathrm {V}}_2{\mathrm {O}}_3$$ V 2 O 3 , with Ni, Permalloy ($${\hbox {Ni}}_{80}{\hbox {Fe}}_{20}$$ Ni 80 Fe 20 ) and Pt layers patterned into a nanoconstriction geometry. The first order phase transition in $${\mathrm {V}}_2{\mathrm {O}}_3$$ V 2 O 3 is shown to lead to systematic changes in the resonance response and hysteretic current control of the ferromagnetic resonance frequency. Further, the output signal can be systematically varied by locally changing the state of the $${\mathrm {V}}_2{\mathrm {O}}_3$$ V 2 O 3 with a dc current. These results demonstrate new spintronic resonator functionalities of interest for neuromorphic computing.

Quantum materials for energy-efficient neuromorphic computing

“…For instance, magnetic oscillator properties can be controlled via the tunable electrical resistance of an adjacent vanadate. 33 Oxides may enable the combination of distinct charge, spin, or superconducting properties for future conversion of information modality from one form to another.…”

“…Electric field effects are particularly promising for controlling spintronic synapses as they are low power, can lead to non-volatile variations, and modify spin textures in multiple ways, e.g., via interfacial effects in oxide/magnetic structures 33,128 or by locally changing the perpendicular anisotropy of the magnetic thin film. A future challenge is to go beyond the neighbor to neighbor coupling intrinsically delivered by exchange or dipolar coupling between the oscillator-neurons, and achieve controllable long range connections.…”

“…However, being able to adjust the output characteristics is not. Incorporating a quantum material -a metal-insulator-transition metal oxide --can give spin resonators hysteresis and memory of their prior state, 33 an important characteristic for oscillator-based synapses (Fig. 7).…”

“…This is because the oscillator characteristics can change dramatically at phase transitions and, at a first order phase transition, can be hysteretic endowing the oscillator with memory, i.e., its resonance frequency and output power can depend on its prior state. 32,33 This can enable learning in a neuromorphic circuit, such as the adjustment of a synaptic weight. The exploration of these ideas has just begun.…”

“…36 Quantum materials may offer additional coupling mechanisms through phase transitions that electrically couple oscillators. 32,33 Tunable or even on/off coupling may be possible at magnetic phase transitions.…”