최경민

Recent observations of switching of magnetic domains in ferromagnetic metals by circularly polarized light, so-called all-optical helicity dependent switching, has renewed interest in the physics that governs the interactions between the angular momentum of photons and the magnetic order parameter of materials. Here we use time-resolved-vectorial measurements of magnetization dynamics of thin layers of Fe, Ni and Co driven by picosecond duration pulses of circularly polarized light. We decompose

Thermal transport in a metallic multilayer on picosecond time scales is controlled by the electronic thermal conductivity (${\ensuremath{\Lambda}}_{e}$), the electronic interfacial thermal conductance (${G}_{ee}$), and electron-phonon coupling constant ($g$). We analyze heat transfer in a nanoscale Pt/Au bilayer using data obtained in pump-probe measurements and modeling using a transmission-line-equivalent circuit. For optical exciation of either the Pt or Au side of the bilayer, the majority o

Spin current generation through the spin-orbit interaction in non-magnetic materials lies at the heart of spintronics. When the generated spin current is injected to a ferromagnet, it produces spin-orbit torque and manipulates magnetization efficiently. Optically generated spin currents are expected to be superior to their electrical counterparts in terms of the manipulation speed. Here we report optical spin-orbit torques in heavy metal/ferromagnet heterostructures. The strong spin-orbit coupli

We measure transient spin accumulation in Cu, Ag, and Au by time-resolved magneto-optical Kerr effect. The transient spin current is generated by ultrafast demagnetization of a ferromagnetic [Co/Pt] layer, and spin accumulates in an adjacent normal metal, Cu, Ag, or Au by spin diffusion. The magnitude of the Kerr rotation is described by an off-diagonal conductivity tensor that is proportional to spin accumulation and spin-orbit coupling. From comparisons between observed Kerr rotations and calc

Ferrimagnetic metals show an extraordinary phenomenon of all-optical switching of magnetization. Ongoing research has revealed the relevant physics of crossing a compensation temperature, occurrence of a transient ferromagneticlike state, and transferring angular momentum between sublattices during the all-optical switching. However, most studies were focused on the spin dynamics of local bands, and the role of the conduction band is unknown. Here, we investigate spin generation in conduction ba

Laser-induced ultrafast demagnetization is an important phenomenon that probes arguably the ultimate limits of the angular momentum dynamics in solid. Unfortunately, many aspects of the dynamics remain unclear except that the demagnetization transfers the angular momentum eventually to the lattice. In particular, the role and origin of electron-carried spin currents in the demagnetization process are debated. Here we experimentally probe the spin current in the opposite phenomenon, i.e., laser-i

We have investigated the feasibility of using FePdB alloy layers for perpendicular magnetic tunnel junctions (p-MTJs). The perpendicular magnetic anisotropy (PMA) of FePdB films is obtained by depositing amorphous Fe40Pd40B20 layers on proper templates and by postannealing. An FePdB film on a thick Pt (001) underlayer has a PMA energy (Ku) of 4.9×106 erg/cm3, and an FePdB layer sandwiched by two thin MgO (001) layers shows a Ku of 3.7×106 erg/cm3. A double barrier p-MTJ with an FePdB middle laye

Metallic ferrimagnets with rare earth-transition metal alloys can provide novel properties that cannot be obtained using conventional ferromagnets. Recently, the compensation point of ferrimagnets, where the net magnetization or net angular momentum vanishes, has been considered a key aspect for memory device applications. For such applications, the magnetic anisotropy energy and damping constant are crucial. In this study, we investigate the magnetic anisotropy and damping constant of a GdCo al