David Cahill1 Hyejin Jang1

1, Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States

Time-resolved measurements of the magneto-optic Kerr effect (TR-MOKE) are commonly used to study how the magnetization dynamics of ferromagnetic materials respond to fast temperature excursions and heat currents generated by ultrafast pulses of light. Here, we flip the situation around and describe how TR-MOKE provides an ultrafast thermometer for studies of the physics of heat conduction. TR-MOKE, i.e., measurements of transient changes in the polarization of a reflected probe beam, has some unique advantages over the more conventional time-domain thermoreflectance (TDTR) approach that is based on measurements of the transient changes in the intensity of a reflected probe beam. For example, the signal in a TR-MOKE measurement is localized to the magnetic layer while the signal from a TDTR measurement is dependent on entire temperature field that interacts with the probe beam. Thus, TR-MOKE can accurately report the temperature of semi-transparent magnetic layers or magnetic layers that are buried within multilayer structures. We are using TR-MOKE to test if the two-temperature model can be applied with consistent parameters to describe ultrafast heat transport in metallic multilayers. Our model system is Pt/Co/Pt trilayers deposited by magnetron sputtering on sapphire substrates. The thickness of the buried magnetic Co layer only 3 atomic layers and yet provides good signal-to-noise and fast time response to the local electronic temperature. We find that the two-temperature model provides a good description of heat transport in Pt over a wide range of length and time-scales.