Synthesis and surface plasmon resonance of Au–ZnO Janus nanostructures

Metal-semiconductor Janus nanostructures with asymmetry and directionality have recently aroused significant interest,both in fundamental light-matter interactions mechanism and in technological applications.Here we report the synthesis of different Au-ZnO Janus nanostructures via a facile one-pot colloid method.The growth mechanism is revealed by a series of designed synthesis experiments.The light absorption properties are determined by both the decrease of dipole oscillations of the free electrons and the plasmon-induced hot-electron transfer.Moreover,the finite-difference time-domain(FDTD)simulation method is used to elucidate the electric field distributions of these Janus nanostructures.

Antiferromagnetic spin dynamics in exchanged-coupled Fe/GdFeO_(3) heterostructure

We investigate the ultrafast spin dynamics of an antiferromagnet in a ferromagnet/antiferromagnet heterostructure Fe/GdFeO_(3) via an all-optical method.After laser irradiation,the terahertz spin precession is hard to be excited in a bare GdFeO_(3) without spin reorientation phase but efficiently in Fe/GdFeO_(3).Both quasi-ferromagnetic and impurity modes,as well as a phonon mode,are observed.We attribute it to the optical modification of interfacial exchange coupling between Fe and GdFeO3.Moreover,the excitation efficiency of dynamics can be modified significantly via the pump laser influence.Our results elucidate that the interfacial exchange coupling is a feasible stimulation to efficiently excite terahertz spin dynamics in antiferromagnets.It will expand the exploration of terahertz spin dynamics for antiferromagnet-based opto-spintronic devices.

Thickness-dependent magnetic anisotropy in obliquely deposited Fe(001)/Pd thin film bilayers probed by VNA-FMR

The thickness-dependent magnetic anisotropy of obliquely deposited Fe(001)/Pd thin films on Mg(001) is investigated by fitting the field-dependent resonant field curve using the Kittel equation.In this study, three Fe film samples with thicknesses of 50 monolayers(ML), 45 ML, and 32 ML deposited at 0°, 45°, and 55°, respectively, are used.The magnetic anisotropy constant obtained from ferromagnetic resonance(FMR) spectra exhibits a dominant fourfold magnetocrystalline anisotropy(MCA) at the normal deposition angle with larger Fe thickness.However, the in-plane uniaxial magnetic anisotropy(UMA) is induced by a higher oblique deposition angle and a smaller thickness.Its hard axis lies between the [100] and [010] directions.The FMR data-fitting analysis yields a precise measurement of smaller contributions to the magnetic anisotropy, such as in-plane UMA.Due to MCA, when the magnetic field is weaker than the saturated field,the magnetization direction does not always align with the external field.The squared frequency-dependent resonant field measurement gives an isotropic Landé g-factor of 2.07.Our results are consistent with previous experiments conducted on the magneto-optical Kerr effect(MOKE) and anisotropic magnetoresistance(AMR) systems.Thus, a vector network analyzer ferromagnetic resonance(VNA-FMR) test-method for finding UMA in obliquely deposited Fe(001)/Pd bilayer ferromagnetic thin films, and determining the magnetic anisotropy constants with respect to the film normal deposition, is proposed.

Anisotropic Magnon–Magnon Coupling in Synthetic Antiferromagnets

Magnon-magnon coupling in synthetic antiferromagnets advances it as hybrid magnonic systems to explore the quantum information technologies.To induce magnon-magnon coupling,the parity symmetry between two magnetization needs to be broken.Here we experimentally demonstrate a convenient method to break the parity symmetry by the asymmetric structure.We successfully introduce a magnon-magnon coupling in Ir-based synthetic antiferromagnets CoFeB(10 nm)/Ir(t_(Ir)=0.6 nm,1.2 nm)/CoFeB(13 nm).Remarkably,we find that the weakly uniaxial anisotropy field(-20 Oe)makes the magnon-magnon coupling anisotropic.The coupling strength presented by a characteristic anticrossing gap varies in the range between 0.54 GHz and 0.90 GHz for t_(Ir)=0.6 nm,and between 0.09 GHz and 1.4 GHz for t_(Ir)=1.2 nm.Our results demonstrate a feasible way to induce magnon-magnon coupling by an asymmetric structure and tune the coupling strength by varying the direction of in-plane magnetic field.The magnon-magnon coupling in this highly tunable material system could open exciting perspectives for exploring quantum-mechanical coupling phenomena.

First-order reversal curve investigated magnetization switching in Pd/Co/Pd wedge film

The magnetization switching plays an essential role in spintronic devices.In this study,a Pd（3 nm）/Co（0.14–1.68 nm）/Pd（5 nm） wedge film is deposited on an Mg O（111） substrate by molecular beam epitaxy.We investigate the polar magneto-optical Kerr effect（MOKE） and carry out the first-order reversal curve（FORC） measurements.For the wedge system,it is observed that the Co thickness could drive the spin reorientation transition（SRT） from out-of-plane to in-plane.Meanwhile,we find the different types of magnetization switchings in the continuous SRT process,which can originate from the formation of different magnetic compositions.Our work provides the possibility of tuning the interfacial effect,and paves the way to analyzing magnetization switching.

Thickness dependent manipulation of uniaxial magnetic anisotropy in Fe-thin films by oblique deposition

The uniaxial magnetic anisotropy of obliquely deposited Fe（001）/Pd film on MgO（001） substrate is investigated as a function of deposition angle and film thickness. The values of incidence angle of Fe flux relative to surface normal of the substrate are 0°, 45°, 55°, and 70°, respectively. In-situ low energy electron diffraction is employed to investigate the surface structures of the samples. The Fe film thicknesses are determined to be 50 ML, 45 ML, 32 ML, and 24 ML（1 ML = 0.14 nm） by performing x-ray reflectivity on the grown samples, respectively. The normalized remanent magnetic saturation ratio and coercivity are obtained by the longitudinal surface magneto-optical Kerr effect. Here, the magnetic anisotropy constants are quantitatively determined by fitting the anisotropic magnetoresistance curves under different fields.These measurements show four-fold cubic anisotropy in a large Fe film thickness（50 ML） sample, but highly in-plane uniaxial magnetic anisotropies in thin films（24 ML and 32 ML） samples. In the obliquely deposited Fe films, the coercive fields and the uniaxial magnetic anisotropies（UMAs） increase as the deposition angle becomes more and more tilted. In addition, the UMA decreases with the increase of the Fe film thickness. Our work provides the possibility of manipulating uniaxial magnetic anisotropy, and paves the way to inducing UMA by oblique deposition with smaller film thickness.

Interfacial effect on the reverse of magnetization and ultrafast demagnetization in Co/Ni bilayers with perpendicular magnetic anisotropy

For static magnetic properties of the Co/Ni bilayers,macroscopic hysteresis loops and microscopic magnetic moment distributions have been determined by the object oriented micromagnetic framework(OOMMF).It is found that when the bilayer systems are fully decoupled,the magnetizations of the two phases reverse separately.The coercivity of the bilayers decreases to a valley value sharply with increasing interfacial exchange coupling and then rises slowly to a platform.On the other hand,we have carried out an atomistic simulation for the laser-induced ultrafast demagnetization of the Co/Ni bilayer.A larger damping constant leads to a faster demagnetization as well as a larger degree of demagnetization,which is consistent with the first-principle theoretical results.For the magnetization recovery process,the damping constant has different influences on the recovery time with various peak electron temperatures,which is ignored in previous atomistic simulations as well as the Landau–Liftshit–Bloch(LLB)micromagnetic calculations.Furthermore,as the interfacial exchange coupling increases,the ultrafast demagnetization curves for Co and Ni become coincident,which is a demonstration for the transition from two-phase phenomenon to single-phase phenomenon.