We have successfully synthesized a single-crystal sample of the layered structure ferromagnet Fe3GeTe2 and present the results of its complete characterization using powder X-ray diffraction (XRD), magnetic susceptibility χ(T), isotherm magnetization \(M(H)\), specific heat \(C(T)\), and electrical resistivity ρ(T) measurements. The rietveld refinement of the powder XRD data confirms that Fe3GeTe2 crystallizes in the space group \(p6_{3}/mmc\). The χ(T), \(C(T)\), and ρ(T) data indicate bulk ferromagnetic ordering at \(T_{\text{C}} = 220\) K with a saturation moment of 1.625 µB/Fe at zero temperature. The magnetic measurements of the external magnetic field \(H\) applied along the \(c\)-axis and \(ab\)-plane show a large anisotropy in this material. We found that the modified Arrott plot (\(M^{4}\)–\(H/M\)) rather than the \(M^{2}\)–\(H/M\) plot is obeyed in this material. The generalized Rhodes–Wohlfarth ratio indicates an itinerant magnetism in this material. The spin fluctuation parameters are estimate...

Magnetic Properties of Layered Itinerant Electron Ferromagnet Fe3GeTe2

Magnetic materials hosting correlated electrons play an important role for information technology and signal processing. The currently used ferro-, ferri- and antiferromagnetic materials provide microscopic moments (spins) that are mainly collinear. Recently more complex spin structures such as spin helices and cycloids have regained a lot of interest.The interest has been initiated by the discovery of the skyrmion lattice phase in noncentrosymmetric helical magnets. In this review we address how spin helices and skyrmion lattices enrich the microwave characteristics of magnetic materials and give rise to bottom-up magnonic crystals. When discussing perspectives for microwave electronics and magnonics we focus particularly on insulating materials as they avoid eddy current losses, offer low spin-wave damping, and allow for electric field control. Thereby, they further fuel the vision of magnonics operated at low energy consumption.

https://iopscience.iop.org/article/10.1088/1361-6463/aa7573/pdf

Collective spin excitations of helices and magnetic skyrmions: review and perspectives of magnonics in non-centrosymmetric magnets

Isolated magnetic vortices are stabilized by an antisymmetric exchange interaction, the so-called Dzyaloshinsky interaction, which can be represented as an energy contribution linear in the first spatial derivatives of the magnetization vector. In contrast, vortex lines are demonstrated to be unstable in the bulk of regular uniaxial ferromagnets. They collapse spontaneously under the influence of anisotropy or an applied magnetic field. In reduced units the differential equation for isolated vortices contains two parameters: the reduced magnetic field h along the crystal axis and the material parameter which describes the relative contribution of the Dzyaloshinsky interaction term. Isolated vortices turn out to be always metastable for large fields, independent of as long as this parameter is positive. At low or negative fields they become unstable by two different mechanisms depending on the -value, but altogether these micromagnetic structures turn out to be stable in a remarkably wide range of parameters. At the end possible applications are considered.

The Properties of Isolated Magnetic Vortices

Fusarium oxysporum is the most economically important and commonly encountered species of Fusarium. This soil-borne fungus is known to harbour both pathogenic (plant, animal and human) and non-pathogenic strains. However, in its current concept F. oxysporum is a species complex consisting of numerous cryptic species. Identification and naming these cryptic species is complicated by multiple subspecific classification systems and the lack of living ex-type material to serve as basic reference point for phylogenetic inference. Therefore, to advance and stabilise the taxonomic position of F. oxysporum as a species and allow naming of the multiple cryptic species recognised in this species complex, an epitype is designated for F. oxysporum. Using multi-locus phylogenetic inference and subtle morphological differences with the newly established epitype of F. oxysporum as reference point, 15 cryptic taxa are resolved in this study and described as species.

/pdf/epitypification-of-fusarium-oxysporum-clearing-the-taxonomic-1qtih44h1g.pdf

Epitypification of Fusarium oxysporum - clearing the taxonomic chaos.

Magnetic materials hosting correlated electrons play an important role for information technology and signal processing. The currently used ferro-, ferri- and antiferromagnetic materials provide microscopic moments (spins) that are mainly collinear. Recently more complex spin structures such as spin helices and cycloids have regained a lot of interest. The interest has been initiated by the discovery of the skyrmion lattice phase in non-centrosymmetric helical magnets. In this review we address how spin helices and skyrmion lattices enrich the microwave characteristics of magnetic materials. When discussing perspectives for microwave electronics and magnonics we focus particularly on insulating materials as they avoid eddy current losses, offer low spin-wave damping, and might allow for electric field control of collective spin excitations. Thereby, they further fuel the vision of magnonics operated at low energy consumption.

Both magnetization and thermal expansion measurements have been made on the same samples of Fe x Co 1- x Si alloys. The magnetization data is analyzed on the basis of the spin fluctuation theory developed by Takahashi to obtain information on the nature of spin fluctuations of this system. We found that concentration variation of magnetic behaviors of the ferromagnetic alloys, such as the Arrott plots and the temperature dependence of spontaneous magnetization, is quantitatively well explained by the theory. Magnetovolume coupling constant is also estimated from thermal expansion coefficient on the basis of the SCR theory over the wide concentration range. The magnetovolume effect is also in good accordance with the predictions of Takahashi's theory, even quantitatively.

Effect of Spin Fluctuations on Magnetic Properties and Thermal Expansion in Pseudobinary System FexCo1-xSi

Measurements of electron spin resonance and magnetization have been performed on the cubic B-20 Fe x Co 1- x Si (0.3≤ x ≤0.85). The magnetization process on Fe 0.8 Co 0.2 Si indicates that this sample is a helimagnet with the cone-ferro-magnetic transition under a low magnetic field. In this sample, the helical spin resonance and the critical field resonance have been observed at 9 GHz at low temperatures, and are similar to those in MnSi observed by Date et al . The helical spin resonance data of Fe 0.8 Co 0.2 Si and MnSi are reasonably explained by the recent magnetic resonance theory for the helical spin structure due to the anti-symmetric exchange interaction existing in the cubic B-20 structure because of the lack of inversion symmetry. In every sample of Fe x Co 1- x Si, ferro- and para- magnetic resonances have been observed at 9 and 24 GHz, and are briefly discussed.

Helical Spin Resonance and Magnetization Measurement in Itinerant Helimagnet Fe x Co 1-x Si (0.3≤x≤0.85)

Ferromagnetic resonance (FRM) measurements were made on [Ni 0.8 Fe 0.15 Co 0.05 /Cu/Co] multilayers in order to observe the coupling between ferromagnetic layers across Cu spacer. The resonant fields vary oscillatory with Cu spacer thickness. The FMR results were analyzed by the resonant model of a magnetically coupled two-layer system. By using a modified RKKY theory for interlayer exchange interaction and FMR results, the coupling constant, J , was determined as a function of Cu spacer thickness. The resonant field can be predicted for Cu spacer thickness and are well compared to the experimental values. In samples of antiferromagnetic coupling, the resonance mode of the magnetization flopping were observed at small applied fields.

Ferromagnetic resonance in [NiFeCo/Cu/Co]-multilayers

https://www.jstage.jst.go.jp/article/jjphytopath1918/59/1/59_1_3/_pdf

Vegetative Compatibility Grouping of Formae Speciales of Fusarium oxysporum Pathogenic to the Liliaceae

Electron spin resonance has been studied at various frequencies (6–24 GHz) on B-20 Fe 0.8 Co 0.2 Si single crystal, which has a long-period helical spin structure (HSS) with a cone-ferromagnetic transition at a critical field H c . Three resonance absorptions have been observed clearly: (a) behaving like a ferromagnetic resonance, (b) occuring around H c and (c) assigned to be a helical spin resonance. The resonance frequency of (c) decreases with increasing the magnetic field. Such dependence does not agree with the resonance theory for a HSS resulting from a competition between symmetric exchange interactions (SEI's), but it agrees well with that for a HSS resulting from a competition between the SEI and the antisymmetric exchange interaction. The present results together with our previous ones give the evidence that the HSS in Fe 0.8 Co 0.2 Si is of the latter type.

Hideki Watanabe

Papers

Effect of Spin Fluctuations on Magnetic Properties and Thermal Expansion in Pseudobinary System FexCo1-xSi

Helical Spin Resonance and Magnetization Measurement in Itinerant Helimagnet Fe x Co 1-x Si (0.3≤x≤0.85)

Ferromagnetic resonance in [NiFeCo/Cu/Co]-multilayers

Vegetative Compatibility Grouping of Formae Speciales of Fusarium oxysporum Pathogenic to the Liliaceae

Helical Spin Resonance in the Cubic B-20 Fe0.8Co0.2Si Single Crystal with a Long-Period Helical Spin Structure