Despite recent advances in exfoliated vdW ferromagnets, the widespread application of 2D magnetism requires a Curie temperature (T_c) above room temperature as well as a stable and controllable magnetic anisotropy. Here we demonstrate a large-scale iron-based vdW material Fe₄GeTe₂ with the T_c reaching ~530 K. We confirmed the high-temperature ferromagnetism by multiple characterizations. Theoretical calculations suggested that the interface-induced right shift of the localized states for unpaired Fe d electrons is the reason for the enhanced T_c, which was confirmed by ultraviolet photoelectron spectroscopy. Moreover, by precisely tailoring Fe concentration we achieved arbitrary control of magnetic anisotropy between out-of-plane and in-plane without inducing any phase disorders. Our finding sheds light on the high potential of Fe₄GeTe₂ in spintronics, which may open opportunities for room-temperature application of all-vdW spintronic devices.

From the applications' point of view, the advantage of low density given by MgB ₂ material must be taken into consideration, and the generation of strong magnetic flux densities using MgB ₂ should be investigated. In this paper, we have studied the magnetic properties of samples processed by a fast spark plasma sintering machine that is able to produce dense and high-quality MgB ₂ samples. Experiments were carried out both on small pieces of the samples and on large-sized samples performing trapped field measurements in a field-cooling process. For temperatures between 10 and 30 K, the results show a strong dependence of the magnetic behavior of the large-sized samples to the applied magnetic field sweep rate, whereas nothing particular appeared on the small samples. As the magnetic flux density produced by MgB ₂ bulks is directly linked to the potential of the applications, we report on the field produced at the surface of one single MgB ₂ sample of 30-mm diameter and the field produced inside a stack of two MgB ₂ samples of 20-mm diameter. A generation of magnetic flux density (magnetic polarization μ ₀ M) up to 4.80 T at 10 K and 3.92 T at 20 K inside the stack of the two MgB ₂ samples was observed under a negative supporting field of -1.47 and -1.95 T, respectively. According to these values to their very low density and to their ease of manufacturing, MgB ₂ bulks are promising materials for the applications of superconductors.

Non-woven superconducting fabrics were prepared by the electrospinning technique, consisting of Bi₂Sr₂CaCuO₈ (Bi-2212) nanowires. The individual nanowires have a diameter of ∼150-200 nm and lengths of up to 100 μm. A non-woven fabric forming a network with a large number of interconnects results, which enables the flow of transport currents through the entire network. We present here magnetization data [M(T) and M(H)-loops] of this new class of superconducting material. The magnetic properties of these nanowire networks are discussed including the irreversibility line and effects of different field sweep rates, regarding the microstructure of the nanowire networks investigated by electron microscopy.

The experimental data in the literature concerning the Paramagnetic Meissner Effect (PME) or also called Wohlleben effect are reviewed with the emphasis on the PME exhibited by metallic, s-wave superconductors. The PME was observed in field-cool cooling (FC-C) and field-cool warming (FC-W) $m\left(T\right)$-measurements on Al, Nb, Pb, Ta, in compounds such as, e.g., NbSe${}_2$, In-Sn, ZrB${}_{12}$, and others, and also in MgB${}_2$, the metallic superconductor with the highest transition temperature. Furthermore, samples with different shapes such as crystals, polycrystals, thin films, bi- and multilayers, nanocomposites, nanowires, mesoscopic objects, and porous materials exhibited the PME. The characteristic features of the PME, found mainly in Nb disks, such as the characteristic temperatures $T_1$ and $T_p$ and the apparative details of the various magnetic measurement techniques applied to observe the PME, are discussed. We also show that PME can be observed with the magnetic field applied parallel and perpendicular to the sample surface, that PME can be removed by abrading the sample surface, and that PME can be introduced or enhanced by irradiation processes. The PME can be observed as well in magnetization loops (MHLs, $m\left(H\right)$) in a narrow temperature window $T_p<T_c$, which enables the construction of a phase diagram for a superconducting sample exhibiting the PME. We found that the Nb disks still exhibit the PME after more than 20 years, and we present the efforts of magnetic imaging techniques (scanning SQUID microscopy, magneto-optics, diamond nitrogen-vacancy (NV)-center magnetometry, and low-energy muon spin spectroscopy, (LE-$\mu$SR)). Various attempts to explain PME behavior are discussed in detail. In particular, magnetic measurements of mesoscopic Al disks brought out important details employing the models of a giant vortex state and flux compression. Thus, we consider these approaches and demagnetization effects as the base to understand the formation of the paramagnetic signals in most of the materials investigated. New developments and novel directions for further experimental and theoretical analysis are also outlined.

This paper presents a comprehensive study of the nonlinear transport properties of magnons electrically emitted or absorbed in extended yttrium-iron garnet (YIG) films by the spin transfer effect across a $\mathrm{YIG}|\mathrm{Pt}$ interface. Our goal is to experimentally elucidate the pertinent picture behind the asymmetric electrical variation of the magnon transconductance, analogous to an electric diode. The feature is rooted in the variation of the density of low-lying spin-wave modes (so-called low-energy magnons) via an electrical shift of the magnon chemical potential. As the intensity of the spin transfer increases in the forward direction (magnon emission regime), the transport properties of low-energy magnons pass through three distinct regimes: (i) at low currents, where the spin current is a linear function of the electric current, the spin transport is ballistic and determined by the film thickness; (ii) for amplitudes of the order of the damping compensation threshold, it switches to a highly correlated regime, limited by the magnon-magnon scattering process and characterized by a saturation of the magnon transconductance. In other words, the reported signal suggests coupled dynamics between numerous modes rather than Bose-Einstein condensation around a single dominant mode. (iii) As the temperature under the emitter approaches the Curie temperature, scattering with high-energy magnons starts to dominate, leading to diffusive transport. We find that such a sequence of transport regimes is analogous to the electron hydrodynamic transport in ultrapure media predicted by Radii Gurzhi, where condensation of magnons. This study, restricted to the low-energy part of the magnon manifold, complements Paper II [Kohno et al., Phys. Rev. B 108, 144411 (2023)] of this series, which focuses on the full spectrum of propagating magnons.

This paper presents a comprehensive study of the spatial dispersion of propagating magnons electrically emitted in extended yttrium-iron garnet (YIG) films by the spin transfer effects across a $\mathrm{YIG}|\mathrm{Pt}$ interface. Our goal is to provide a generic framework to describe the magnon transconductance inside magnetic films. We experimentally elucidate the relevant spectral contributions by studying the lateral decay of the magnon signal. While most of the injected magnons do not reach the collector, the propagating magnons can be split into two fluids: (i) a large fraction of high-energy magnons carrying energy of about $k_B{T}_0$, where $T_0$ is the lattice temperature, with a characteristic decay length in the submicrometer range, and (ii) a small fraction of low-energy magnons, which are particles carrying energy of about $\hslash {\omega }_K$, where ${\omega }_K/\left(2\pi \right)$ is the Kittel frequency, with a characteristic decay length in the micrometer range. Taking advantage of their different physical properties, the low-energy magnons can become the dominant fluid (i) at large spin transfer rates for the bias causing the emission of magnons, (ii) at large distance from the emitter, (iii) at small film thickness, or (iv) for reduced band mismatch between the YIG below the emitter and the bulk due to variation of the magnon concentration. This broader picture complements a companion paper [R. Kohno et al., Phys. Rev. B 108, 144410 (2023)], which focuses solely on the nonlinear transport properties of low-energy magnons.