Iron mono-arsenide in the powder form has been investigated by transmission 57Fe Moessbauer spectroscopy in the temperature range 4.2 - 1000 K. Additional spectra have been obtained at 20 K and 100 K applying external magnetic field of 7 T. It was found that the spin spiral propagating along the c-axis leads to the complex variation of the hyperfine magnetic field amplitude with the spin orientation varying in the a-b plane. The magnitude of the hyperfine field pointing in the direction of the local magnetic moment depends on the orientation of this moment in the a-b plane. Patterns are vastly different for iron located in the [0 k 0] positions and for iron in the [0 k+1/2 0] positions within the orthorhombic cell set to the Pnma symmetry. Lattice softens upon transition to the paramagnetic state at 69.2 K primarily in the a-c plane as seen by iron atoms. This effect is quite large considering lack of the structural transition. Two previously mentioned iron sites are discernible in the paramagnetic region till 300 K by different electron densities on the iron nuclei. The anisotropy of the iron vibrations developed at the transition to the paramagnetic state increases with the temperature in accordance with the harmonic approximation, albeit tends to saturation at high temperatures indicating gradual onset of the quasi-harmonic conditions. It seems that neither hyperfine fields nor magnetic moments are correct order parameters in light of the determined static critical exponents. Sample starts to loose arsenic at about 1000 K and under vacuum.
The attainability of modification of the apparent magnetic anisotropy in (III,Mn)V ferromagnetic semiconductors is probed by means of the finite-elements-based modelling. The most representative case of (Ga,Mn)As and its in-plane uniaxial anisotropy is investigated. The hysteresis loops of the continuous films of a ferromagnetic semiconductor as well as films structured with the elliptic antidots are modelled for various eccentricity, orientation, and separation of the anti dots. The effect of anti-dots on the magnetic anisotropy is confirmed but overall is found to be very weak. The subsequen…
The magnetic structure of the iron monoarsenide FeAs is studied using first-principles calculations. We consider the collinear and non-collinear (spin-spiral wave) magnetic ordering and magnetic anisotropy. It is analitically shown that a magnetic triaxial anisotropy results in a sum of two spin-spiral waves with opposite directions of wave vectors and different spin amplitudes, so that the magnetic moments in two perpendicular directions do not equal each other.
Continuous miniaturization of magnetic units in spintronics and quantum computing devices inspires efforts to search for magnetic nanostructures with large magnetic anisotropy energy (MAE). Typical nanostructures including molecular magnets, magnetic nanoclusters and magnetic nanowires have MAEs of a few meV so their blocking temperature is mostly lower than 50 K. In this work, we demonstrated the feasibility of achieving giant MAE in systems with transition metal dimers on defected and decorated graphene, based on density functional theory calculations. In particular, either a Pt-Ir dimer on …
Sr2VO{3-delta}FeAs superconductors with different oxygen deficiencies have been successfully fabricated. It is found that the superconducting transition temperature drops down monotonically with the increase of oxygen deficiency. The diminishing of superconductivity is accompanied by the enhancement of residual resistivity, indicating an unraveled scattering effect induced by the oxygen deficiency. The highest superconducting transition temperature at about 40 K is achieved near the stoichiometrical sample Sr$_2$VO$_{3}$FeAs. Surprisingly, the X-ray photoelectron spectroscopy (XPS) shows that …
Bottom-up assembly of optically nonlinear and magnetically anisotropic lanthanide materials involving precisely placed spin carriers and optimized metal-ligand coordination offers a potential route to developing electronic architectures for coherent radiation generation and spin-based technologies, but the chemical design historically has been extremely hard to achieve. To address this, we developed a worthwhile avenue for creating new noncentrosymmetric chiral Ln3+ materials Ln2(SeO3)2(SO4)(H2O)2 (Ln = Sm, Dy, Yb) by mixed-ligand design. The materials exhibit phase-matching nonlinear optical …
The dynamics of magnetic domain walls along ferromagnetic strips with spatially modulated perpendicular magnetic anisotropy is theoretically studied by means of micromagnetic simulations. Ferromagnetic layers with a periodic sawtooth profile of the anisotropy depict a well-defined set of energy minima where the walls are pinned in the absence of external stimuli, and favor the unidirectional propagation of domain walls. The performance of the current-driven domain wall motion along these ratchet-like systems is compared to the field-driven case. Our study indicates that the current-driven doma…
Magnetic tunnel junction (MTJ) based on CoFeB/MgO/CoFeB structures is of great interest due to its application in the spin-transfer-torque magnetic random access memory (STT-MRAM). Large interfacial perpendicular magnetic anisotropy (PMA) is required to achieve high thermal stability. Here we use first-principles calculations to investigate the magnetic anisotropy energy (MAE) of MgO/CoFe/capping layer structures, where the capping materials include 5d metals Hf, Ta, Re, Os, Ir, Pt, Au and 6p metals Tl, Pb, Bi. We demonstrate that it is feasible to enhance PMA by using proper capping materials…
Spin torque oscillators (STOs) are emerging microwave devices that can potentially be used in spin-logic devices and the next-generation high-speed computing architecture. Thanks to their non-linear nature, STOs are easily tunable by the magnetic field and the dc current. Spin Hall nano-oscillators (SHNOs) are promising types of STOs and most of the current studies focus on localized modes that can be easily excited. Here, we study using micromagnetic simulations, the nature of the spin-torque-induced excitations in nanowire devices made of perpendicular magnetic anisotropy (PMA) material. Our…
The Fe(1+x)Sb compound has been synthesized close to stoichiometry with x = 0.023(8). The compound was investigated by 57Fe Mössbauer spectroscopy in the temperature range 4.2 - 300 K. The antiferromagnetic ordering temperature was found as 232 K i.e. much higher than for the less stoichiometric material. Regular iron was found to occupy two different positions in proportion 2:1. They differ by the electric quadrupole coupling constants and both of them exhibit extremely anisotropic electric field gradient tensor (EFG) with the asymmetry parameter equal one. The negative component of both EFGs…
We study realizations of spirals and skyrmions in two-dimensional antiferromagnets with a triangular lattice on an inversion-symmetry-breaking substrate. As a possible material realization, we investigate the adsorption of transition-metal atoms (Cr, Mn, Fe, or Co) on a monolayer of MoS$_2$, WS$_2$, or WSe$_2$ and obtain the exchange, anisotropy, and Dzyaloshinskii-Moriya interaction parameters using first-principles calculations. Using energy minimization and parallel-tempering Monte-Carlo simulations, we determine the magnetic phase diagrams for a wide range of interaction parameters. We fin…
Complete Raman Tensor Determination in Birefringent $β$-Ga$_2$O$_3$ by Single-Stage Hyperspectral Analysis of Polarization Angle-Resolved Raman Spectra
Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V.（柏林莱布尼茨固体电子学保罗·德鲁德研究所）；Technische Universität Berlin（柏林工业大学）；Leibniz-Institut für Kristallzüchtung（莱布尼茨晶体生长研究所）；Institut de Ciència de Materials de Barcelona, ICMAB-CSIC（巴塞罗那材料科学研究所）
In search of novel, improved materials for magnetic data storage and spintronic devices, compounds that allow a tailoring of magnetic domain shapes and sizes are essential. Good candidates are materials with intrinsic anisotropies or competing interactions, as they are prone to host various domain phases that can be easily and precisely selected by external tuning parameters such as temperature and magnetic field. Here, we utilize vector magnetic fields to visualize directly the magnetic anisotropy in the uniaxial ferromagnet CeRu$_2$Ga$_2$B. We demonstrate a feasible control both globally and…
We report on the vapor-solid growth of single crystalline few-layer MoS2 films on (0001)-oriented sapphire with excellent structural and electrical properties over centimeter length scale. High-resolution X-ray diffraction scans indicated that the films had good out-of-plane ordering and epitaxial registry. A carrier density of ~2 x 1011 cm-2 and a room temperature mobility of 192 cm2/Vs were extracted from space-charge limited transport regime in the films. The electron mobility was found to exhibit in-plane anisotropy with a ratio of ~ 1.8. Theoretical estimates of the temperature-dependent …
The two-dimensional Heisenberg exchange model with out-of-plane anisotropy and a Dzyaloshinskii-Moriya interaction is employed to investigate the lifetime and stability of antiferromagnetic (AFM) skyrmions as a function of temperature and external magnetic field. An isolated AFM skyrmion is metastable at zero temperature in a certain parameter range set by two boundaries separating the skyrmion state from the uniform AFM phase and a stripe domain phase. The distribution of the energy barriers for the AFM skyrmion decay into the uniform AFM state complements the zero-temperature stability diagr…
