Materials with extraordinary spin/heat coupling
Ella Pek, Hyejin Jang, Zhu Diao and David G. Cahill
OSU subcontract; prime: Army Research Office MURI W911NF-14-1-0016

Together with collaborators at Ohio State University, U. of Chicago, and UCLA, we are working to understand both heat currents carried by spin excitations as well as spin currents created by heat currrents. The coupling of spin and heat gives rise to new physical phenomena in nanoscale spin devices and new ways to manipulate local magnetization. This field of study is typically referred to as “spin caloritronics”. Our work in this field takes advantage of recent advances in the measurement and understanding of heat transport at the nanoscale using ultrafast lasers. We use a picosecond duration pump laser pulses as a source of heat and picosecond duration probe laser pulses to detect changes in temperature, spin accumulation, and spin transfer torque using a combination of time-domain thermoreflectance and time-resolved magneto-optic Kerr effect Our pump-probe optical methods enable us to change the temperature of ferromagnetic layers on a picosecond time-scale and generate enormous heat fluxes on the order of 100 GW m-2 that persist for  30 ps.

Low-dimensional quantum magnets based on copper oxides (Sr14Cu24O41, La2CuO4, CaCu2O3), demonstrate that electrons and phonons are not the only significant carriers of heat in materials. Near room temperature, the magnon thermal conductivity is comparable to the electronic thermal conductivities of metal alloys. At high modulation frequencies, the thermal conductivity is reduced by non-equilibrium between phonons and magnons on short length scales. We extract the effective strength of magnon-phonon coupling from the TDTR data using a two temperature model.

---

File translated from T_EX by T_TH, version 4.12.
On 25 Aug 2018, 16:38.