Special Condensed Matter Seminar - Chunhui Du, Ohio State U - " Spin Dynamics and Transport Studied by Ferromagnetic Resonance (FMR) based Techniques"

Fri, Apr 10, 2015, 1:00 pm to 2:00 pm
Jadwin A07
Generation and manipulation of spin is of central importance in modern physics. This intense interest is driven in part by exciting new phenomena such as spin Hall effects and spin transfer torque as well as by the growth in new tools enabling microscopic studies. Ferromagnetic resonance (FMR) is a powerful technique to study both macro and nano-scale spin ensembles, and also an effective method to generate pure spin currents. In the first part of my talk, we use FMR spin pumping technique to characterize the spin Hall angles for a series of 3d, 4d, and 5d transition metals with widely varying spin-orbit coupling strengths and demonstrate that both atomic number Z and d-electron count play important roles in spin Hall physics. We have systematically studied spin transport in a series of six Y3Fe5O12/insulator/Pt trilayers where the inserted insulators have different magnetic properties: diamagnetic (one), paramagnetic (one) and antiferromagnetic (AF) (four, having a wide range of magnetic ordering temperatures). We observe remarkably robust spin transport in the AF insulators and a clear linear relationship between the spin decay lengths in the insulators and the damping enhancements in the Y3Fe5O12, suggesting the critical role of magnetic correlations in magnetic insulators for spin transport. I will then describe our experiment using spin wave modes confined into microscopic volumes in a ferromagnetic film by the spatially inhomogeneous magnetic field of a scanned micromagnetic tip of a ferromagnetic resonance force microscope (FMRFM). We have measured local spin transfer from the resonance region to surrounding areas within an insulating ferrimagnetic Y3Fe5O12 thin film, and we image the local magnetic texture variations in patterned ferromagnetic permalloy structures. Micromagnetic simulations accurately reproduce our FMRFM spectra allowing quantitative understanding of the spin dynamics and transport phenomena across various interfaces. I will also show strong coupling of FMR excitation to spins in Nitrogen Vacancy (NV) center in diamond, suggesting NV center is a promising candidate to image the spin dynamics.