Search

Ferroelectric Rashba semiconductors (FERSCs) have recently attracted intensive attention due to their giant bulk Rashba parameter, αR, which results in a locking between the spin degrees of freedom and the switchable electric polarization. However, the integration of FERSCs into microelectronic devices has provoked questions concerning whether the Rashba effect can persist when the material thickness is reduced to several nanometers. Here we find that αR can keep a large value of 2.12 eV A in the 5.0 nm thick GeTe film. The behavior of αR with thickness can be expressed by the scaling law and provides a 3D thickness limit of the bulk Rashba effect, dc = 2.1 ± 0.5 nm. Finally, we find that the thickness can modify the Berry curvature as well, which influences the polarization and consequently alters the αR. Our results give insight into understanding the factors influencing αR in FERSCs and pave a novel route for designing Rashba-type quantum materials.

We characterize the magnetic interfacial coupling of the Fe/FeGe heterostructure and its influence on the magnetic damping via ferromagnetic resonance in the temperature range of 200-300 K. When the temperature is below the critical temperature of FeGe, the interfacial coupling rises. The strength of the magnetic interfacial coupling is determined as a function of the temperature and reaches up to 0.194 erg/cm2 at 200 K. Meanwhile, the Gilbert damping of the Fe layer is enhanced from 0.035 at 300 K to 0.050 at 200 K. The enhancement is linearly proportional to the strength of magnetic interfacial coupling. We attribute the enhancement to the interfacial coupling that transfers spin angular momentum from Fe to FeGe via the exchange interaction. Our results reveal that the interfacial coupling is an effective approach to inject spin current into the chiral spin texture.

Dual topological insulators, simultaneously protected by time-reversal symmetry and crystalline symmetry, open great opportunities to explore different symmetry-protected metallic surface states. However, the conventional dual topological states located on different facets hinders integration into planar opto-electronic/spintronic devices. Here, we construct dual topological superlattices (TSLs) Bi

Topological insulators (TIs) have emerged as some of the most efficient spin-to-charge convertors because of their correlated spin-momentum locking at helical Dirac surface states. While endeavors have been made to pursue large "charge-to-spin" conversions in novel TI materials using spin-torque-transfer geometries, the reciprocal process "spin-to-charge" conversion, characterized by the inverse Edelstein effect length (λ

Chiral bobber (ChB) is an exotic three-dimensional topological texture in chiral magnets. It is composed of a Bloch-point singularity and a skyrmion tube; the incommensurate characteristic length scales of these two components would thus lead to novel dynamics of a ChB. Here, we report the current-induced motion and the accompanying Hall effect of a ChB. Surprisingly, we find that the Hall angle of a ChB can be tuned in a wide range from \ensuremath{-}90 \ifmmode^\circ\else\textdegree\fi{} to positive angles. A further study of spin-wave excitations identified high-frequency resonant modes, which are related to the velocity of ChB and lattice constants. The excited frequency can be two orders of magnitude higher than that of skyrmions. The broad ranges of Hall angles and frequency spectra could boost the development of spintronic devices using topological textures.

Although the magnetic relaxation mechanism in ferromagnetic/nonmagnetic (FM/NM) bilayers has been commendably established, the nonlocal Gilbert damping has been much less addressed in spin valve configurations of FM/NM/FM associated with both the static interlayer exchange coupling and the dynamic coupling. Here, we report the dimensional crossover role of the Pd layer on magnetic relaxation in Fe/Pd/Fe trilayer structures. We identify a pronounced jump of Gilbert damping across the characteristic static interlayer exchange coupling length of Fe/Pd/Fe. The significant enhancement and suppression of Gilbert damping values are ascribed to the entanglement of the dynamics of the two Fe layers mediated by the static exchange coupling and the dynamic exchange coupling. Our work deepens the understanding to manipulate the spin transport and magnetic relaxation via the coherence of spin current.

The magnon-magnon coupling in synthetic antiferromagnets advances it as hybrid magnonic systems to explore the quantum information technologies. To induce the 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 thickness of two magnetic layers and thus introduce a magnon-magnon coupling in Ir-based synthetic antiferromagnets CoFeB(10 nm)/Ir(tIr=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 tIr =0.6 nm, and between nearly zero to 1.4 GHz for tIr = 1.2 nm, respectively. Our results demonstrate a feasible way to induce the 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., 19 pages, 3 figures

$\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{PdB}{\mathrm{i}}_{2}$ has attracted much attention for its prospective ability to possess simultaneously topological surface and superconducting states due to its unprecedented spin-orbit interaction (SOC). Whereas most works have focused solely on investigating its topological surface states, the coupling between spin and charge degrees of freedom in this class of quantum material remains unexplored. Here, we report a study of spin-to-charge conversion in a $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{PdB}{\mathrm{i}}_{2}$ ultrathin film grown by molecular beam epitaxy, utilizing a spin pumping technique to perform inverse spin Hall effect measurements. We find that the room temperature spin Hall angle of $\mathrm{Fe}/\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{PdB}{\mathrm{i}}_{2}$, ${\ensuremath{\theta}}_{SH}=0.037$. This value is one order of magnitude larger than that of reported conventional superconductors, and is comparable to that of the best SOC metals and topological insulators. Our results provide an avenue for developing superconductor-based spintronic applications.

We investigate the ultrafast spin dynamics of an antiferromagnet in a ferromagnet/antiferromagnet heterostructure Fe/GdFeO3 via an all-optical method. After laser irradiation, the terahertz spin precession is hard to be excited in a bare GdFeO3 without spin reorientation phase but efficiently in Fe/GdFeO3. 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.

The spin pumping effect of CoFeB/Ir bilayers has been investigated via the broadband ferromagnetic resonance measurement. With increasing the thickness of heavy metal Ir layer, the Gilbert damping factor of 8 nm CoFeB film increases from 7 × 10−3 to 1.1 × 10−2, and the additional damping factors induced by the spin pumping effect quickly reaches its saturation value. According to the spin pumping theory, the spin mixing conductance of CoFeB/Ir and the spin diffusion length of Ir were obtained. The spin mixing conductance is 2.14 × 1019 m−2. Furtherly, the spin diffusion length is only 1.34 nm, which is quite shorter compared with the heavy metal Pt. Our results reveal the existence of the strong spin-orbit coupling in the heavy metal Ir, which can be a potential material for the application in spintronic devices.

The anisotropic behavior of Gilbert damping provides a new dimension for controlling and tuning magnetization relaxation within the same magnetic device. The single-crystalline ferromagnetic metals with a high symmetry have been predicted to possess significantly anisotropic damping for one decade. By decreasing temperature down to T = 4.5 K, we found that the anisotropic damping factor Q, defined as the fractional difference of damping between easy and hard axis, can be approached to 60%–90% in Fe (15 nm)/MgO (0 0 1) without applied fields dependent behavior. It is much larger than Q = 10%–20% obtained at room temperature. Furthermore, it is followed by explanations on the basis of the breathing Fermi surface model giving around Q = 30%–40% when electron-phonon scattering rate is small enough. This discovery will enrich the understanding of damping mechanism, and can provide clues for searching strongly anisotropic damping within 3d transition metals and alloys.

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.

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.

First-principles calculations are made on the Ge1−xMnxTe diluted magnetic semiconductors with different compositions. The origin of their ferromagnetism is investigated and the carrier-induced ferromagnetism is developed for these diluted magnetic semiconductors. The Mn 3d states localized with divalent character are deep below the Fermi level, and the carriers introduced by defects are supported in our calculation. The p states of Ge also play an important role in the occurrence of ferromagnetism especially at high temperature. It is thought that Ge1−xMnxTe with a moderate composition (x = 0.51) of Mn atoms is a good candidate for DMS materials.

Exchange biasing and magnetoresistance (MR) behaviors have been investigated in La0.67Ca0.33MnO3/La0.5Ca0.5MnO3 bilayers with specially designed interfacial structures. The exchange coupling is found to be strongly related to interfacial structures. Exchange field H-E decreases as the cooling field N-fc increases at high H-fc region. Especially, the coercivity H-C is enhanced by exchange coupling for bilayers with rough interface, while it is reduced for relatively smooth interface. Also, large low-field MR has been achieved by introducing regular in-plane grain boundaries, and a biasing of R-H loop has been observed.