Spin dynamics of electrons in the first excited subband of a high-mobility low-density 2D electron system

We report on time-resolved Kerr rotation measurements of spin coherence of electrons in the first excited subband of a high-mobility low-density two-dimensional electron system in a GaAs/Al0.35Ga0.65As heterostructure. While the transverse spin lifetime (T2*) of electrons decreases monotonically with increasing magnetic field, it has a non-monotonic dependence on the temperature, with a peak value of 596 ps at 36 K, indicating the effect of inter-subband electron-electron scattering on the electron spin relaxation. The spin lifetime may be long enough for potential device application with electrons in excited subbands

Directional Spin Wave in Spin-Torque Oscillators Induced by Interfacial Dzyaloshinskii–Moriya Interaction

Spin torque oscillators (STOs) are currently of great interest due to its wide tunable frequencies, low energy consumption and high quality factors compared with traditional oscillators. Here, we report the characteristics of the nanocontact-(NC-)STO in the presence of interfacial Dzyaloshinskii-Moriya interaction (DMI), using micromagnetic simulations. We find that the DMI can decrease the STO frequency by around 2 GHz. More importantly, the DMI is able to break the isotropy of the spin-wave spectrum and turn the emitted microwave into directional spin-wave beams potentially facilitating the synchronization of multiple STOs

Femtosecond laser-heating effect on the magnetization dynamics in perpendicularly magnetized Ta/CoFeB/MgO film

We have studied the effect of ultrafast laser-heating on the magnetization dynamics of perpendicularly magnetized CoFeB film by means of the time-resolved magneto-optical Kerr rotation effect. The effective perpendicular magnetic anisotropy field HK is significantly decreased with enhancing the pump laser-fluence in a moderate range of 5-12 mJ cm-2. The Gilbert damping, however, is found to be independent of the pump fluence. These findings provide a new method of separately manipulating the Gilbert damping and perpendicular magnetic anisotropy

Enhanced magnetoresistance in NiFe/GaAs/Fe hybrid magnon valve

The magnon valve (MV), which consists of a one spacer layer sandwiched between two ferromagnetic layers, is a potential spintronic device. The operation principle of the magnon valve depends on magnon current propagating between the two magnetic layers. More specifically, the magnon current is induced in one ferromagnetic layer and then injects magnons into the other ferromagnetic layer through the spacer layer. During this process, the magnetization of the injected ferromagnetic layer is changed, leading to the different relative magnetic orientations of the two magnetic layers. Here, we investigated the electromagnetic property of the NiFe/GaAs/Fe magnon valve assisted by microwaves with various frequencies. We find that the magnetoresistance (MR) of the magnon valve increases up to 40% when applying an external 3.4GHz microwave. The increase in the magnetoresistance results from the magnon current propagating between the two ferromagnetic layers. The magnons induced by the external microwave share the same phase, and thus the magnon current can penetrate into a 70 μm thick GaAs by coherent propagation

Transient enhancement of magnetization damping in CoFeB film via pulsed laser excitation

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

Transient enhancement of magnetization damping in CoFeB film via pulsed laser excitation

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

Component manipulated magnetic anisotropy and damping in Heusler-like compound Co2+xFe1-xAl

The component dependence of the magnetocrystalline anisotropy and the damping has been investigated in epitaxial Heusler-like compound Co2+xFe1-xAl films grown by molecular beam epitaxy (MBE) with x = -0.4, -0.2, 0, 0.2, and 0.4. All the films show a component tunable four-fold magnetocrystalline anisotropy with the easy axis along [1 1 0] orientation. The time resolved magneto-optic Kerr effect measurements reveal that the damping constant can be tuned in a range of 0.0065-0.0156 with a minimum value of 0.0065 at x = -0.2. This work provides a new approach to manipulate the magnetic dynamic properties of Heusler alloy Co2FeAl by adjusting the proportion of Co and Fe

Depinning of domain walls in permalloy nanowires with asymmetric notches

E ective control of the domain wall (DW) motion along the magnetic nanowires is of great importance for fundamental research and potential application in spintronic devices. In this work, a series of permalloy nanowires with an asymmetric notch in the middle were fabricated with only varying the width (d) of the right arm from 200 nm to 1000 nm. The detailed pinning and depinning processes of DWs in these nanowires have been studied by using focused magneto-optic Kerr e ect (FMOKE) magnetometer, magnetic force microscopy (MFM) and micromagnetic simulation. The experimental results unambiguously exhibit the presence of a DW pinned at the notch in a typical sample with d equal to 500 nm. At a certain range of 200 nm < d < 500 nm, both the experimental and simulated results show that the DW can maintain or change its chirality randomly during passing through the notch, resulting in two DW depinning elds. Those two depinning elds have opposite d dependences, which may be originated from di erent potential well/barrier generated by the asymmetric notch with varying d

Observation of Small Polaron and Acoustic Phonon Coupling in Ultrathin La0.7Sr0.3MnO3/SrTiO3 Structures

Understanding the underlying physics of interactions among various quasi-particles is a fundamental issue for the application of spintronics and photonics. Here the observation of a coupling between the small polarons in the nanoscale ultrathin La0.7Sr0.3MnO3 (LSMO) films and the acoustic phonons in the SrTiO3 (STO) substrate using ultrafast pump–probe spectroscopy has been reported. According to the temperature- and wavelength-dependent measurements, the amplitudes of the acoustic phonons are suppressed by tuning the small polarons absorption. This shows a coupled relationship between the acoustic phonons and the small polarons. At the probe photon energy of 1.55 eV where the polaron absorption is dominant, the acoustic phonons become unobservable. Furthermore, by performing the pump fluence dependent measurements on the LSMO films with different thicknesses, smaller acoustic phonon amplitudes are found in the thinner film with stronger small polaron binding energy. Such a coupled nature can be utilized to manipulate the small polarons using the acoustic phonons or vice versa, which is of great importance in device applications of colossal magnetoresistance materials

Interface magnetic and electrical properties of CoFeB /InAs heterostructures

Amorphous magnetic CoFeB ultrathin films have been synthesized on the narrow band gap semiconductor InAs(100) surface, and the nature of the interface magnetic anisotropy and electrical contact has been studied. Angle-dependent hysteresis loops reveal that the films have an in-plane uniaxial magnetic anisotropy (UMA) with the easy axis along the InAs [0-11] crystal direction. The UMA was found to be dependent on the annealing temperatures of the substrates, which indicates the significant role of the Fe, Co-As bonding at the interface related to the surface condition of the InAs(100). I-V measurements show an ohmic contact interface between the CoFeB films and the InAs substrates, which is not affected by the surface condition of the InAs (100)