Recent discovery of intrinsic ferromagnetism in two-dimension (2D) van der Waals (vdW) crystals has opened up a new arena for spintronics, raising an opportunity of achieving the tunable intrinsic 2D vdW magnetism. Here, we show that the magnetization and the magnetic anisotropy energy (MAE) of the few-layered Fe3GeTe2 (FGT) is strongly modulated by a femtosecond (fs) laser pulse. Upon increasing the fs laser excitation intensity, the saturation magnetization increases in an approximately linear way and the coercivity determined by the MAE, decreases monotonically, showing unambiguously the effect of the laser pulse on magnetic ordering. This effect observed at room temperature reveals the emergence of the lightdriven room-temperature (300K) ferromagnetism in the 2D vdW FGT as its intrinsic Curie temperature is ~ 200 K. The light-tunable ferromagnetism is attributed to the changes in the electronic structure due to the optical doping effect. Our findings pave a novel way to optically tune the 2D vdW magnetism and enhance the up to the room temperature, promoting spintronic applications at or above the room temperature.

Laser-induced spin dynamics of in-plane magnetized CoFeB films has been studied by using time-resolved magneto-optical Kerr effect measurements. While the effective demagnetization field shows little dependence on the pump laser fluence, the intrinsic damping constant has been found to be increased from 0.008 to 0.076 with the increase in the pump fluence from 2 mJ/cm2 to 20 mJ/cm2. This sharp enhancement has been shown to be transient and ascribed to the heating effect induced by the pump laser excitation, as the damping constant is almost unchanged when the pump-probe measurements are performed at a fixed pump fluence of 5 mJ/cm2 after irradiation by high power pump pulses.

Nanoscale Fe 3 O 4 epitaxial thin film has been synthesized on MgO/GaAs(100) spintronic heterostructure, and studied with X-ray magnetic circular dichroism (XMCD). We have observed a total magnetic moment (m l+s ) of (3.32±0.1)µ B /f.u., retaining 83% of the bulk value. Unquenched orbital moment (m l ) of (0.47µ B ±0.05)µ B /f.u. has been confirmed by carefully applying the sum rule. The results offer direct experimental evidence of the bulk-like total magnetic moment and a large orbital moment in the nanoscale fully epitaxial Fe 3 O 4 /MgO/GaAs(100) heterostructure, which is significant for spintronics applications. Liu et al. CITATION:

Ultrathin films of magnetite ͑Fe 3 O 4 ͒ have been grown epitaxially on wurtzite wide bandgap semiconductor GaN͑0001͒ surfaces using molecular-beam epitaxy. Reflection high-energy electron-diffraction patterns show a ͑111͒ orientation of the Fe 3 O 4 films and in-plane epitaxial relationship of ͗110͘ Fe 3 O 4 ʈ ͗1120͘ GaN and ͗112͘ Fe 3 O 4 ʈ ͗1100͘ GaN with the GaN͑0001͒. X-ray photoelectron spectroscopy and x-ray magnetic circular dichroism confirm the growth of stoichiometric Fe 3 O 4 , instead of ␥ -Fe 2 O 3 . The magnetic hysteresis loops and saturation magnetization M s obtained by superconducting quantum interference device at room temperature show fast saturation of the Fe 3 O 4 films with the magnetization close to that of the bulk single-crystal value. In-plane magnetoresistance ͑MR͒ measurements reveal negligibly small MR effects, further indicating that the films are free from antiphase boundaries.

Enhanced spin pumping damping in yttrium iron garnet/Pt bilayers Appl. Phys. Lett. 102, 012402 (2013) Mapping microwave field distributions via the spin Hall effect Appl. Phys. Lett. 101, 252406 (2012) Enhancing exchange bias and tailoring microwave properties of FeCo/MnIr multilayers by oblique deposition J. Appl. Phys. 112, 113908 (2012) Transmission of microwaves through exchange-coupled bi-layer magnetic films in ferromagnetic and standing spin wave resonances J. Appl. Phys. 112, 093901 (2012) Room temperature microwave-assisted recording on 500-Gbpsi-class perpendicular medium J. Appl. Phys. 112, 083912 (2012) Additional information on J. Appl. Phys. Optical pump-probe spectroscopy has been used to observe damped ferromagnetic resonance ͑FMR͒ oscillations in thin film Fe samples. The FMR was pumped by magnetic field pulses generated by an optically triggered photoconductive switch, and probed by means of time resolved measurements of the magneto-optical Kerr rotation. The photoconductive switch structure consisted of a parallel wire transmission line, of 125 m track width and separation, defined on a semi-insulating GaAs substrate. The biased transmission line was optically gated at one end so that a current pulse propagated along the transmission line to where the sample had been overlaid. The magnetic field associated with the current pulse is spatially nonuniform. By focusing the probe beam on the sample at different points above the transmission line the effect of the orientation of the pump field has been studied. The gyroscopic motion of the magnetization has been modeled by solving the Landau-Lifshitz-Gilbert equation and the magneto-optical response of the sample has been calculated by taking account of both the longitudinal and polar Kerr effects. The calculated and measured magneto-optical Kerr rotations are found to be in reasonable agreement.