98 research outputs found
Composition-tuned magneto-optical Kerr effect in L10-MnxGa films with giant perpendicular anisotropy
We report the large polar magnetooptical Kerr effect in L10-MnxGa epitaxial
films with giant perpendicular magnetic anisotropy in a wide composition range.
The Kerr rotation was enhanced by a factor of up to 10 by decreasing Mn atomic
concentration, which most likely arises from the variation of the effective
spin-orbit coupling strength, compensation effect of magnetic moments at
different Mn atom sites, and overall strain. The Kerr ellipticity and the
magnitude of the complex Kerr angle is found to have more complex
composition-dependence that varies with the photon energy. These L10-MnxGa
films show large Kerr rotation of up to 0.10o, high reflectivity of 35%-55% in
a wide wavelength range of 400~850 nm, and giant magnetic anisotropic field of
up to 210 kOe, making them an interesting material system for emerging
spintronics and terahertz modulator applications
Observation of orbital two-channel Kondo effect in a ferromagnetic L10-MnGa film
The experimental existence and stability of the quantum criticality point of
the two-channel Kondo (2CK) effect displaying exotic non-Fermi liquid physics
has been buried in persistent confusion despite the intensive theoretical and
experimental efforts in past three decades. Here we report an experimental
realization of the two-level system scattering-induced orbital 2CK effect in a
ferromagnetic L10-MnGa film, which is signified by a magnetic field-independent
resistivity upturn that has a logarithmic and square-root temperature
dependence beyond and below the Kondo temperature of ~14.5 K, respectively. Our
result not only evidences the robust existence of orbital 2CK effect even in
the presence of strong magnetic fields and long-range ferromagnetic ordering
but also extends the scope of 2CK host materials from nonmagnetic nanoscale
point contacts to diffusive conductors of disordered alloys
Effective exchange interaction for terahertz spin waves in iron layers
The exchange stiffness is a central material parameter of all ferromagnetic materials. Its value controls the Curie temperature as well as the dynamic properties of spin waves to a large extent. Using ultrashort spin current pulses we excite perpendicular standing spin waves (PSSW) in ultrathin epitaxial iron layers at frequencies of up to 2.4 THz. Our analysis shows that for the PSSWs the observed exchange stiffness of iron is about 20% smaller compared to the established iron bulk value. In addition, we find an interface-related reduction of the effective exchange stiffness for layers with the thickness below 10 nm. To understand and discuss the possible mechanisms of the exchange stiffness reduction we develop an analytical one-dimensional model. In doing so we find that the interface induced reduction of the exchange stiffness is mode dependent
Modulating the polarization of broadband terahertz pulses from a spintronic emitter at rates up to 10 kHz
Reliable modulation of terahertz electromagnetic waveforms is important for many applications. Here, we rapidly modulate the direction of the electric field of linearly polarized terahertz electromagnetic pulses with 1–30 THz bandwidth by applying time-dependent magnetic fields to a spintronic terahertz emitter. Polarity modulation of the terahertz field with more than 99% contrast at a rate of 10 kHz is achieved using a harmonic magnetic field. By adding a static magnetic field, we modulate the direction of the terahertz field between angles of, for instance, −53° and 53° at kilohertz rates. We believe our approach makes spintronic terahertz emitters a promising source for low-noise modulation spectroscopy and polarization-sensitive techniques such as ellipsometry at 1–30 THz
Laser-induced terahertz spin transport in magnetic nanostructures arises from the same force as ultrafast demagnetization
Laser-induced terahertz spin transport (TST) and ultrafast demagnetization (UDM) are central but so far disconnected phenomena in femtomagnetism and terahertz spintronics. Here, we show that UDM and TST are driven by the same force: a generalized spin voltage, which is induced by the incident femtosecond laser pulse. Using broadband terahertz emission spectroscopy, we find that the rate of UDM of a single ferromagnetic film F has the same time evolution as the flux of TST from F into an adjacent normal-metal layer N. An analytical model consistently and quantitatively explains our observations. It reveals that both UDM in F and TST in the F|N stack arise from a generalized spin voltage Δμs, which is defined for arbitrary, nonthermal electron distributions. Our findings open up unexpected synergies and new pathways toward large-amplitude terahertz spin currents and, thus, energy-efficient ultrafast spintronic devices
Extremely Nonperturbative Nonlinearities in GaAs Driven by Atomically Strong Terahertz Fields in Gold Metamaterials
Magnetic anisotropies in ultrathin iron films grown on the surface-reconstructed GaAs substrate
Magnetic anisotropies of epitaxial ultrathin iron films grown on the surface-reconstructed GaAs substrate were studied. Ferromagnetic resonance technique was exploited to determine magnetic parameters of the films in the temperature range of 4-300 K. Extraordinary angular dependence of the FMR spectra was explained by the presence of fourfold and twofold in-plane anisotropies. A strong in-plane uniaxial anisotropy with magnetic hard axis along the [1 1- 0] crystallographic direction is present at the GaAsFe (001) interface while a weak in-plane uniaxial anisotropy for the Fe grown on Au has its easy axis oriented along [1 1- 0]. A linear dependence of the magnetic anisotropies as a function of temperature suggests that the strength of the in-plane uniaxial anisotropy is affected by the magnetoelastic anisotropies and differential thermal expansion of contacting materials. © 2007 American Institute of Physics
Terahertz-Driven Nonlinear Spin Response of Antiferromagnetic Nickel Oxide
Terahertz magnetic fields with amplitudes of up to 0.4 Tesla drive magnon resonances in nickel oxide while the induced dynamics is recorded by femtosecond magneto-optical probing. We observe distinct spin-mediated optical nonlinearities, including oscillations at the second harmonic of the 1 THz magnon mode. The latter originate from coherent dynamics of the longitudinal component of the antiferromagnetic order parameter, which are probed by magneto-optical effects of second order in the spin deflection. These observations allow us to dynamically disentangle electronic from lattice-related contributions to magnetic linear birefringence and dichroism-information so far only accessible by ultrafast THz spin control. The nonlinearities discussed here foreshadow physics that will become essential in future subcycle spin switching
Extremely non-perturbative terahertz nonlinearities in GaAs metamaterials
erahertz near fields of gold metamaterials resonant at a frequency of 0.88 THz allow us to enter an extreme limit of nonperturbative ultrafast terahertz electronics: Fields reaching a ponderomotive energy in the keV range are exploited to drive nondestructive, quasistatic interband tunneling and impact ionization in undoped bulk GaAs, injecting electron-hole plasmas with densities in excess of 1019 cm−3. This process causes bright luminescence at energies up to 0.5 eV above the band gap and induces a complete switch-off of the metamaterial resonance accompanied by self-amplitude-modulation of transmitted few-cycle terahertz transients. Our results pave the way towards highly nonlinear terahertz optics and optoelectronic nanocircuitry with subpicosecond switching times
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