Phase-Sensitive Imaging of Ferromagnetic Resonance Using Ultrafast Heat Pulses

Abstract

Measuring local magnetization dynamics and its spatial variation is essential for advancements in spintronics and relevant applications. Here we demonstrate a phase-sensitive imaging technique for studying patterned magnetic structures based on picosecond laser heating. With the timeresolved anomalous Nernst effect (TRANE) and extensions, we simultaneously image the dynamic magnetization and RF driving current density. The stroboscopic detection implemented in TRANE microscopy provides access to both amplitude and phase information of ferromagnetic resonance (FMR) and RF current. Using this approach, we measure the spatial variation of the Oersted driving field angle across a uniform channel. In a spatially nonuniform sample with a cross shape, a strong spatial variation for the RF current as well as FMR precession is observed. We find that both the amplitude and the phase of local FMR precession are closely related to those of the RF current.

Ferromagnetic resonance phase imaging in spin Hall multilayers

“…The driving current has a controllable phase, and it is frequency-locked to the stroboscopic repetition rate of the laser pulses, thus enabling measurement of the FMR with a selectable relative phase between the driving current phase and the probe time. Additionally, the increase in the local resistivity due to transient heating produces a voltage corresponding to the stroboscopic time-slice of I rf , enabling us to image the local driving current amplitude and phase 31 . For materials with a large longitudinal spin Seebeck effect (LSSE) 35 , the vertical thermal gradient will also generate a voltage signal proportional to m y , if the ferromagnetic layer is interfaced with a spin Hall material (like Pt) because of the inverse spin Hall effect.…”

“…In this work, we use time-resolved anomalous Nernst effect (TRANE) microscopy 30,31 to quantify spin Hall efficiency by detecting local ferromagnetic resonance (FMR) precession phase in spin Hall multilayers. By imaging the amplitude and phase of the precessing magnetization in relation to the driving current, we find that the driving field direction in a sample with strong spin torque is different from that in a sample where the spin torque is blocked with a 2 nm thick Hf spacer.…”

Imaging uncompensated moments and exchange-biased emergent ferromagnetism in FeRh thin films

“…Unlike anomalous Nernst images of ferromagnets 23,25,26 , V AN E does not uniformly saturate with the field, which indicates that it does not originate from simple ferromagnetism. We can rule out possible spurious contributions from spatial inhomogeneity in sample resistivity or thermal conductivity, for two reasons.…”

Imaging Magnetization Structure and Dynamics in Ultrathin Y3Fe5O12/Pt Bilayers with High Sensitivity Using the Time-Reso

“…This relation is used to fit the FMR spectra to extract the amplitude, phase, linewidth, and resonant field. For more details on fitting see refs [25,38]. To demonstrate that the TRLSSE microscope is a phase-sensitive stroboscope, we rotated the phase of the microwave current by 180° and remeasure FMR.…”