ULTRAFAST MAGNETIZATION SWITCHING OF FERROMAGNETIC ALLOYS THROUGH OPTICALLY GENERATED SPIN CURRENT
Divyashish Kumar1, Richard Wilson2, Jeffrey Bokor2.
1College of San Mateo, San Mateo, CA, 2University of California, Berkeley, Berkeley, CA.
Current methods of controlling the magnetization dynamics of a ferromagnetic metal for storin information have substantial limitations, especially with regards to processing speed and data storage density. Magnetization switching by spin-transfer-torque is a promising phenomenon for the operation of ultrafast nanoscale devices. In our study, we investigated the possibility of using optically generated spin current to manipulate the magnetization of a 0.5 nm ferromagnetic layer. The spin current is generated by the rapid demagnetization of a ferromagnetic metal with the use of an ultrashort laser pulse. To understand the experimental limitations, we developed numerical simulations that compare the measured temperature dependence of the remnant magnetization with the optically generated temperature rises in order to calculate the spin currents in 4 different ferromagnetic metals: Fe, Ni, Co50Fe50, and Ni43Fe57. From this model, we predict that Ni43Fe57 excited with a 100 fs laser pulse with a fluence of 25 Jm-2 can generate a net spin current of approximately 1010 A/s for approximately 0.5 ps. The model also suggests that 1010 A/s is the spin current threshold for switching the spin of a 0.5 nm layer of Co50Fe50B. This investigation allows us to explore new ways of generating spin currents to flip the magnetization of a ferromagnetic film on the timescale of a few picoseconds.