  Metal-insulator transitions (MITs) in resistive switching materials can be
triggered by an electric stimulus that produces significant changes in the
electrical response. When these phases have distinct magnetic characteristics,
dramatic changes in spin excitations are also expected. The transition metal
oxide La0.7Sr0.3MnO3 (LSMO) is a ferromagnetic metal at low temperatures and a
paramagnetic insulator above room temperature. When LSMO is in its metallic
phase a critical electrical bias has been shown to lead to an MIT that results
in the formation of a paramagnetic resistive barrier transverse to the applied
electric field. Using spin-transfer ferromagnetic resonance spectroscopy, we
show that even for electrical biases less than the critical value that triggers
the MIT, there is magnetic phase separation with the spin-excitation resonances
varying systematically with applied bias. Thus, applied voltages provide a
means to alter spin resonance characteristics of interest for neuromorphic
circuits.
