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Magnetic materials are essential for energy generation and information devices, and they play an important role in advanced technologies and green energy economies. Currently, the most widely used magnets contain rare earth (RE) elements. An outstanding challenge of notable scientific interest is the discovery and synthesis of novel magnetic materials without RE elements that meet the performance and cost goals for advanced electromagnetic devices. Here, we report our discovery and synthesis of an RE-free magnetic compound, Fe 3 CoB 2 , through an efficient feedback framework by integrating machine learning (ML), an adaptive genetic algorithm, first-principles calculations, and experimental synthesis. Magnetic measurements show that Fe 3 CoB 2 exhibits a high magnetic anisotropy ( K 1 = 1.2 MJ/m 3 ) and saturation magnetic polarization ( J s = 1.39 T), which is suitable for RE-free permanent-magnet applications. Our ML-guided approach presents a promising paradigm for efficient materials design and discovery and can also be applied to the search for other functional materials.

Topological phase in magnetic materials yields a quantized contribution to the Hall effect known as the topological Hall effect, which is often caused by skyrmions, with each skyrmion creating a magnetic flux quantum h/e. The control and understanding of topological properties in nanostructured materials is the subject of immense interest for both fundamental science and technological applications, especially in spintronics. In this work, the electron-transport properties and spin structure of exchange-coupled cobalt nanoparticles with an average particle size of 13.7 nm are studied experimentally and theoretically. Magnetic and Hall-effect measurements identify topological phase transitions in the exchange-coupled cobalt nanoparticles and were used to discover a qualitatively new type of hysteresis in the topological Hall effect namely, Berry-phase hysteresis. Micromagnetic simulations reveal the origin of the topological Hall effect namely, the chiral domains, with domain-wall chirality quantified by an integer skyrmion number. These spin structures are different from the skyrmions formed due to Dzyaloshinskii Moriya interactions in B20 crystals and multilayered thin films, and caused by cooperative magnetization reversal in the exchange-coupled cobalt nanoparticles. An analytical model is developed to explain the underlying physics of Berry-phase hysteresis, which is strikingly different from the iconic magnetic hysteresis and constitutes one aspect of 21st-century reshaping of our view on nature at the borderline of physics, chemistry, mathematics, and materials science., Comment: 29 pages and 16 images

Neutron powder diffraction (NPD) and x-ray magnetic circular dichroism (XMCD) spectroscopy are employed to investigate the magnetism and spin structure in single-phase B20 Co1.043Si0.957. The magnetic contributions to the NPD data measured in zero fields are consistent with the helical order among the allowed spin structures derived from group theory. The magnitude of the magnetic moment is (0.3 ± 0.1)μB/Co according to NPD, while the surface magnetization probed by XMCD at 3 kOe is (0.18–0.31)μB/Co. Both values are substantially larger than the bulk magnetization of 0.11μB/Co determined from magnetometry at 70 kOe and 2 K. These experimental data indicate the formation of a helical spin phase and the associated conical states in high magnetic fields.

New magnetic materials for energy and information-processing applications are of paramount importance in view of significant global challenges in environmental and information security. The discovery and design of materials requires efficient computational and experimental approaches for high throughput and efficiency. When increasingly powerful computational techniques are combined with special non-equilibrium fabrication methods, the search can uncover metastable compounds with desired magnetic properties. Here we review recent results on novel Fe-, Co- and Mn-rich magnetic compounds with high magnetocrystalline anisotropy, saturation magnetization, and Curie temperature created by combining experiments, adaptive genetic algorithm searches, and advanced electronic-structure computational methods. We discuss structural and magnetic properties of such materials including Co– and/or Fe–X compounds (X = N, Si, Sn, Zr, Hf, Y, C, S, Ti, or Mn), and their prospects for practical applications.

L10 highly ordered FePt nanostructures were successfully synthesized following a direct one-step liquid phase chemical approach. The enhanced ordering was achieved with the use of bismuth additives...

The structural, magnetic and electron-transport properties of Fe2Ti0.5Co0.5Si are investigated. It is demonstrated that rapidly quenched Fe2Ti0.5Co0.5Si ribbons crystallize in the L21 structure, indicating a full Heusler compound, and exhibit ferromagnetism with a high Curie temperature of about 790 K. Moreover, Fe2Ti0.5Co0.5Si exhibits semiconducting behavior with a negative temperature coefficient of resistivity, a room-temperature resistivity of about 6.5 mΩ cm and a residual resistivity ρ0 of about 6.75 mΩ cm. The carrier concentration n is 1.15 × 1020 cm−3 at 5 K. The magnetic semiconducting behavior with a high Curie temperature makes this material promising for room-temperature spintronic and magnetic applications.

Magnetotransport and ferromagnetism in thin films of ${\mathrm{Co}}_{2}\mathrm{Si}$ nanoclusters are investigated experimentally and theoretically. The nanoclusters are fabricated by an inert-gas condensation-type cluster-deposition method and have an average size of 11.3 nm. Unlike the bulk ${\mathrm{Co}}_{2}\mathrm{Si}$ that exhibits a very weak net magnetic moment only below 10 K, the nanoclusters exhibit room-temperature ferromagnetism with a substantial saturation magnetization. Key features of the system are its closeness to the Stoner transition, magnetic moments induced by spin polarization starting from surface atoms, and nonuniaxial anisotropy associated with the orthorhombic crystal structure of ${\mathrm{Co}}_{2}\mathrm{Si}$. A method is introduced to determine the effective anisotropy using the experimental magnetization data of this complex system and its relationship with the two lowest-order nonuniaxial anisotropy constants. On decreasing temperature from 300 K, the nanoclusters show electron-transport properties unusual for a ferromagnetic metal, including an increase of Hall resistivity and a nonmonotonic change of negative magnetoresistance with a peak at around 100 K. The underlying physics is explained on the basis of the large polarization of surface spins and variation in the degree of their misalignments due to temperature-dependent effective anisotropy.

MnBi and MnBi-based materials have been investigated as prospective rare-earth-free permanent magnets with moderate energy product. One of the main issues with MnBi synthesis is the presence of residual Bi in the sample which reduces the net magnetization. We have found that MnBi synthesized in the presence of carbon substantially reduces the amount of residual Bi, improving its saturation magnetization. We have synthesized Mn55Bi45 and Mn55Bi45C x samples using arc melting and high-vacuum annealing. The room temperature x-ray diffraction patterns indicate that both Mn55Bi45 and Mn55Bi45C x crystallize in the hexagonal NiAs-type structure. The Rietveld analysis of the x-ray patterns shows that the amount of residual Bi reduces from 16 wt.% for Mn55Bi45 to 5 wt.% for Mn55Bi45Cx. The high-field (3 T) magnetizations measured at room temperature are 61 emu g−1 and 66 emu g−1 for Mn55Bi45 and Mn55Bi45C x , respectively. To understand the role of C in enhancing the magnetization of MnBi, we carried out the first-principles calculations of both stoichiometric and nonstoichiometric MnBi alloys, which suggests that the increase of magnetization in Mn55Bi45C x may be due to the coating of MnBi grains with C.

An open-access database specialized for magnetic compounds, as well as for magnetic clusters, is developed with a focus on magnets free from rare earths. Data-intensive methods are used to facilitate the theoretical and experimental design and discovery of new magnetic materials. The utility of the datasets for computational screening, machine-learning modeling, and experimental fabrication is discussed.

The realization of the magnetic moment of Mn atoms in ferromagnetic alloys is investigated theoretically. This paper is partly motivated by the recent discovery of high-magnetization Fe–Co–Mn thin films by Snow et al. , who reported moments of up to 3.25 $\mu _{\text {B}}$ per atom. Structural and strain effects are discussed with particular emphasis on the distinction between tetragonal martensitic lattice distortions and Bain transitions in body-centered cubic, CsCl, and Heusler alloys. It is outlined how these lattice distortions affect the electronic structure of the alloys, and ab initio calculations are used to determine the net moment of cubic Fe6Co63Mn31. The calculated moment, $2.90~\mu _{\text {B}}$ per atom, is reasonably close to the experimental value.

Permanent magnets (PM) are critical components for electric motors and power generators. Key properties of permanent magnets, especially coercivity and remanent magnetization, are strongly dependent on microstructure. Understanding metallurgical processing, phase stability and microstructural changes are essential for designing and improving permanent magnets. The widely used PM for the traction motor in electric vehicles and for the power generator in wind turbines contain rare earth elements Nd and Dy due to their high maximum energy product. Dy is used to sustain NdFeB's coercivity at higher temperature. Due to the high supply risk of rare earth elements (REE) such as Dy and Nd, these elements are listed as critical materials by the U.S. Department of Energy and other international institutes. Other than Dy, finer grain size is also found to have effect on sustaining coercivity at higher temperature. A proper control of phase stability and microstructures has direct impact on mitigating REE supply risk. Compared to rare earth PMs, non-rare earth (non-RE) PMs typically have lower maximum energy products, however, given their small supply risks and low cost, they are being intensively investigated for less-demanding applications. The general goal for the development of non-RE PMs is to fill in the gap between the most cost-effective but low performing hard ferrite magnet and the most expensive but high performing RE PMs. In the past five years great progress has been made toward improving the microstructure and physical properties of non-RE PMs. Several new candidate materials systems were investigated, and some have showed realistic potential for replacing RE PMs for some applications. In this article, we review the science and technology of various types of non-RE materials for PM applications. These materials systems include Mn based, high magnetocrystalline anisotropy alloys (MnBi and MnAl compounds), spinodally decomposing alloys (Alnico), high-coercivity tetrataenite L10 phase (FeNi and FeCo), and nitride/carbide systems (such as α" based, high saturation magnetization Fe16N2 type phase and Co2C/Co3C acicular particle phase). The current status, challenges, potentials as well as the future directions for these candidates non-RE magnet materials are discussed.

Heusler compounds and alloys based on them are of great recent interest because they exhibit a wide variety of spin structures, magnetic properties, and electron-transport phenomena. Their properties are tunable by alloying and we have investigated L21-orderd compound Ru2MnSn and its alloys by varying the atomic Mn:Sn composition. While antiferromagnetic ordering with a Neel temperature of 361 K was observed in Ru2MnSn, the Mn-poor Ru2Mn0.8Sn1.2 alloy exhibits properties of a diluted antiferromagnet in which there are localized regions of uncompensated Mn spins. Furthermore, a noncoplanar spin structure, evident from a topological Hall-effect contribution to the room-temperature Hall resistivity, is realized in Ru2Mn0.8Sn1.2. Our combined experimental and theoretical analysis shows that in the Ru2Mn0.8Sn1.2 alloy, the magnetic properties can be explained in terms of a noncoplanar antiferromagnetic scissor mode, which creates a small net magnetization in a magnetic field and subsequently yields a Berry curvature with a strong topological Hall effect.

Mn-containing Heuslers are important magnetic shape-memory alloys for fast and precise actuators in manufacturing, robotics, surgery, and other applications. Among the key requirements are a high magnetization and favorable thermal properties, especially a high Curie temperature. In this work, the effect of Fe and Co substitution on the structure and magnetism of Mn2NiSn alloys is investigated. The Heusler alloys have been produced by melt spinning and characterized by X-ray diffraction, magnetometry, and electron-transport measurements. It was found that Co substitution for Mn enhances the Curie temperature of Mn2NiSn and both Co and Fe substitution improve its magnetization. These improvements are accompanied by reduced thermal and magnetic hysteresis losses and by interesting structural changes, namely improved chemical order and site occupancies characteristic of quaternary (Y-ordered) Heuslers.

Alloys with nominal compositions of Mn2CrGa1-xAlx (x = 0.0, 0.2, 0.5, 1.0) have been studied by X-ray powder diffraction (XRD). Detailed structural investigation of the alloys with x = 0.2 and 0.5 has been further carried out using transmission electron microscopy (TEM). The alloys, in the typical Heusler composition, were prepared using rapid quenching and subsequent annealing. The XRD analysis revealed that a disordered cubic phase was present in the alloys with x = 0.0 and 1.0 while a spinodal decomposition with phase separation has been observed in the alloys with x = 0.2 and 0.5. TEM study confirms a segregation of two crystalline phases, one of them a cubic phase with the β–Mn prototype structure and the other a new crystalline phase with a tetragonal structure. Energy-dispersive X-ray spectroscopy (EDS) analysis was used to determine the compositions of the two crystalline phases. The mass ratio of the tetragonal phase and the β–Mn prototype cubic phase is derived as t/c ≈ 2.41 by fitting the average compositions of the two crystalline phases to the nominal composition. The orientational relationship of two crystalline structures has been determined by selected-area electron diffraction (SAED) and stereogram analysis. The structures of the two crystalline phases have been investigated by high-resolution transmission electron microscopy (HRTEM) and image simulation. The structural model of the tetragonal phase is proposed and compared with the experimental results in SAED and HRTEM studies.

We present a study of perpendicular magnetic anisotropy in [Co/Ni(t)/Co/Pt]×8 multilayers for use as free layers in magnetic tunnel junctions (MTJ) and spin valves. The thickness t of the Ni sub-layer was varied and the resulting magnetic properties were investigated. As determined from magnetic force microscopy and magnetometry measurements, all multilayers exhibited a perpendicular magnetic anisotropy with an increase of saturation magnetization with thickness t. From the temperature dependence of the magnetization, well described by a Bloch law, we find that the spin-wave stiffness constant of the [Co/Ni(t)/Co/Pt]×8 multilayers is larger compared to (Co/Ni) multilayers. These multilayers could be the basis for spintronic devices where the reduction of total Pt content could help to reduce the damping constant while keeping the magnetic anisotropy energy relatively high. These are conflicting requirements needed for high performance magnetic memory devices.

Rhombohedral Zr 2 Co 11 -based materials have shown very promising magnetic properties, but this rhombohedral phase is elusive and metastable. In this study, nanocrystalline Zr 2 Co 11 films were obtained by magnetron co-sputtering on Si (100) substrate with the in-situ annealing. Temperature dependence of magnetic domain structure and magnetic properties of nanocrystalline Zr 2 Co 11 have been investigated. Proper in-situ annealing temperature enhances the content of hard magnetic phase and improves the magnetic properties. Compared with Zr 2 Co 11 thin films grown at low temperature (823 K) and higher temperatures, thin films with in-situ annealing temperature of 1023 K have coercivity B c ( B c = μ 0 H c ) of 0.15 T and energy product BH max of 16.0 kJ/m 3 . Magnetic Force Microscopy images show the highest bright-dark magnetic domain contrast with highest root-mean-square values of the phase shift for thin film with in-situ annealing temperature of 1023 K. These findings have correlated magnetic domain structure and magnetic properties of Zr 2 Co 11 thin films, and elaborated the effect of different in-situ annealing temperatures on magnetic domain structure.

An orientation memory effect in high density polyethylene (HDPE) filled with vapor grown carbon nanofibers (VGCNF) is reported. Two-dimensional X-ray (2DXR) confirmed the reorientation of HDPE crystallites upon the uniaxial stretching of HDPE and HDPE filled by VGCNFs. This anisotropy of 2DXR spectra was decreased by heating all stretched samples (loaded or not loaded by VGCNFs) from room to the melting temperature of HDPE. Upon cooling these samples to room temperature, it was noticed that only the nanocomposite retained a weak partial (uniaxial) order, while HDPE showed a completely isotropic 2DXR spectrum. It was concluded that during the stretching of nanocomposites the crystallites and VGCNFs were aligned along the uniaxial stress. Upon heating, the crystalline phase was melted, while the orientation of the VGCNFs was not significantly disturbed. The recrystallization of the polymer started preferentially from the VGCNF – polymer interphase, resulting into an anisotropic crystalline structure.

The magnetization of noninteracting metallic nanoparticles is investigated by comparing the particle-size and temperature dependences of the magnetization for several mechanisms. The nanoparticle magnetization deviates from that of the underlying bulk materials due to zero-temperature and thermal effects, and on a mean-field level, the corresponding surface-core interaction is described by a Landau–Ginzburg approach. A major factor is the reduced atomic coordination at the surface, which has often, but not always, opposite effects on the zero-temperature magnetization and Curie temperatures. The coordination effect is particularly pronounced for very weak itinerant ferromagnets and for strongly exchange-enhanced Pauli paramagnets. With regard to external magnetic fields, the nanoparticle magnetization involves several “superparamagnetic” phenomena, namely, Neel relaxation, Brownian relaxation, and Langevin macrospin paramagnetism.

The structural and magnetic properties of Co2Ge nanoparticles (NPs) prepared by the cluster-beam deposition (CBD) technique have been investigated. As-made particles with an average size of 5.5 nm exhibit a mixture of hexagonal and orthorhombic crystal structures. Thermomagnetic measurements showed that the as-made particles are superparamagnetic at room temperature with a blocking temperature (TB) of 20 K. When the particles are annealed at 823 K for 12 h, their size is increased to 13 nm and they develop a new orthorhombic crystal structure, with a Curie temperature (TC) of 815 K. This is drastically different from bulk, which are ferromagnetic at cryogenic temperatures only. X-ray diffraction (XRD) measurements suggest the formation of a new Co-rich orthorhombic phase (OP) with slightly increased c/a ratio in the annealed particles and this is believed to be the reason for the drastic change in their magnetic properties.

Structural and magnetic properties of iron-free and iron-substituted $\mathrm{SmC}{\mathrm{o}}_{5}$ have been investigated theoretically and experimentally. The nanocrystalline ribbons of ${\mathrm{SmCo}}_{5\ensuremath{-}x}{\mathrm{Fe}}_{x}\phantom{\rule{4pt}{0ex}}(0\ensuremath{\le}x\ensuremath{\le}2)$, which were produced by rapid solidification, crystallize in the hexagonal $\mathrm{CaC}{\mathrm{u}}_{5}$ structure for $x\ensuremath{\le}0.75$. Small Fe additions $(x=0.25)$ substantially improve the coercivity, from 0.45 to 2.70 T, which we interpret as combined intrinsic and extrinsic effect. Most of our findings are consistent with past samarium-cobalt research, but some are at odds with findings that have seemingly been well established through decades of rare-earth transition-metal research. In particular, our local spin-density approximation with Hubbard parameter calculations indicate that the electronic structure of the Sm atoms violates Hund's rules and that the orbital moment is strongly quenched. Possible reasons for the apparent disagreement between theory and experiment are discussed. We explicitly determine the dependence of the Sm $4f$ charge distribution, arguing that an accurate density-functional description of $\mathrm{SmC}{\mathrm{o}}_{5}$ is a challenge to future research.

Magnets with chiral crystal structures and helical spin structures have recently attracted much attention as potential spin-electronics materials, but their relatively low magnetic-ordering temperatures are a disadvantage. While cobalt has long been recognized as an element that promotes high-temperature magnetic ordering, most Co-rich alloys are achiral and exhibit collinear rather than helimagnetic order. Crystallographically, the B20-ordered compound CoSi is an exception due to its chiral structure, but it does not exhibit any kind of magnetic order. Here, we use nonequilibrium processing to produce B20-ordered ${\mathrm{Co}}_{1+x}{\mathrm{Si}}_{1\ensuremath{-}x}$ with a maximum Co solubility of $x=0.043$. Above a critical excess-Co content (${x}_{c}=0.028$), the alloys are magnetically ordered, and for $x=0.043$, a critical temperature ${T}_{c}=328\text{ }\text{ }\mathrm{K}$ is obtained, the highest among all B20-type magnets. The crystal structure of the alloy supports spin spirals caused by Dzyaloshinskii-Moriya interactions, and from magnetic measurements we estimate that the spirals have a periodicity of about 17 nm. Our density-functional calculations explain the combination of high magnetic-ordering temperature and short periodicity in terms of a quantum phase transition where excess-cobalt spins are coupled through the host matrix.

Neutron powder diffraction has been used to investigate the spin structure of the hard-magnetic alloy $\mathrm{F}{\mathrm{e}}_{3+x}\mathrm{C}{\mathrm{o}}_{3\ensuremath{-}x}\mathrm{T}{\mathrm{i}}_{2}$ ($x=0,2,3$). The materials are produced by rapid quenching from the melt, they possess a hexagonal crystal structure, and they are nanocrystalline with crystallite sizes $D$ of the order of 40 nm. Projections of the magnetic moment onto both the crystalline $c$ axis and the basal plane were observed. The corresponding misalignment angle exhibits a nonlinear decrease with $x$, which we explain as a micromagnetic effect caused by Fe-Co site disorder. The underlying physics is a special kind of random-anisotropy magnetism that leads to the prediction of $1/{D}^{1/4}$ power-law dependence of the misalignment angle on the crystallite size.

The onset of ferromagnetism in cobalt-tin alloys is investigated experimentally and theoretically. The $\mathrm{C}{\mathrm{o}}_{1+x}\mathrm{Sn}$ alloys were prepared by rapid quenching from the melt and form a modified hexagonal NiAs-type crystal structure for $0.45\ensuremath{\le}x\ensuremath{\le}1$. The magnetic behavior is described analytically and by density-functional theory using supercells and the coherent-potential approximation. The excess of Co concentration $x$, which enters the interstitial $2d$ sites in the hypothetical NiAs-ordered parent alloy CoSn, yields a Griffiths-like phase and, above a quantum critical point $({x}_{c}\ensuremath{\approx}0.65)$, a quantum phase transition to ferromagnetic order. Quantum critical exponents are determined on the paramagnetic and ferromagnetic sides of the transition and related to the nature of the magnetism in itinerant systems with different types of chemical disorder.

Rapidly quenched ternary Ni-Mn-T (T = In, Sn) alloys exhibit features associated with magnetic skyrmions, so that XRD, TEM, EDS, SAED and HREM investigations were carried out for structural characterization on the two alloy systems. In this paper, we report a new type of Mn-rich Heusler compound with a cubic unit cell, a = 0.9150 nm in Ni-Mn-In and a = 0.9051 nm in Ni-Mn-Sn, which coexist with a Ni-rich full-Heusler compound with defects, a = 0.6094 nm in Ni-Mn-In and a = 0.6034 nm in Ni-Mn-Sn. A further analysis of the experimental results reveals a close structural relationship between these two compounds.

Crystal structure and magnetic properties of Heusler alloys MnXNiSn (X = Mn, Fe, Co) are investigated using density functional theory and compared with experimental results. The parent alloy Mn2NiSn, which crystallizes in the inverse Heusler structure, is found to be ferrimagnetic, in agreement with previous experimental and theoretical work. The Fe and Co substitutions cause the alloys to assume a fairly well-ordered Y structure and enhance the magnetization substantially. We find that the strong nearest neighbour Mn-X exchange changes from antiferromagnetic (X = Mn) to ferromagnetic (X = Fe, Co), which explains and actually overestimates the experimental changes. A striking feature of the system is that Fe and Co have opposite effects on the Curie temperature Tc: they reduce and enhance Tc, respectively. We qualitatively explain this behaviour in terms of two-sublattice model based on the nearest-neighbour exchange.

The manuscript focuses on the dispersion of magnetic nanoparticles within self-assembling block copolymers, on the preferential localization of nanoparticles and on the effect of their concentration on the magnetic properties of the nanocomposites and on the self-assembly features of the matrix. Carbon-coated nickel nanoparticles dispersed within polystyrene–block polyisoprene–block polystyrene have been investigated by Raman, X-ray, SQUID, differential scanning calorimetry, and electron microscopy. The effect of nanofiller on the self-assembly features of the block copolymer is reported. Preferential localization of nanofiller within the soft phase was noticed below 20 wt% nanofiller. Higher loadings with nanoparticles showed an uniform distribution of nanofiller within the block copolymer, consistent with the destruction of self-assembly. The effect of nanoparticles’ concentration on blocking temperature is discussed.

The structural and magnetic properties of Nd12Fe82B6 and Nd10M2Fe82B6 (M = Nb, Ti, Zr, Cr) alloys prepared using arc melting and melt spinning have been investigated. All the samples are found to crystallise with a tetragonal Nd2Fe14B phase without any alloy or elemental impurities. There is a small decrease in the unit cell volume of Nd2Fe14B due to transition metal (M) addition. The substitution of Nb and Ti refines and homogenises the nanostructure of the alloys, promoting intergrain exchange coupling leading to an increase in the remanence and energy product. For example, the remanence and energy product of Nd12Fe82B6 and Nd10Nb2Fe82B6 are 8.4 kG and 15 MGOe, and 9.9 kG and 20 MGOe, respectively. The J(T) curves are similar to those of a single phase ferromagnetic material suggesting no segregation of ferromagnetic impurities. The observed structural and magnetic properties are consistent with the fact that the substitutional transition metal atoms occupy the Nd site of the tetragonal Nd2Fe14B...

Intermetallic compounds having compositions from HfCo 4 to HfCo 8 were investigated by transmission electron microscopy, selected-area electron diffraction, and energy-dispersive x-ray spectroscopy. A major crystalline phase, closely related to the orthorhombic Zr 2 Co 11 phase in structure, has been observed in the samples with the composition ranges from HfCo 6 to HfCo 8 . The phase, referred to as either Hf 2 Co 11 or HfCo 7 phase in the literature, is actually one common phase, having a broad composition range and referred to as μ -phase in the present paper. In addition to the μ -phase, we have found coexisted fcc-Co phase and a minor Hf 2 Co 7 phase. The Hf 6 Co 23 phase has been identified in the HfCo 4 and HfCo 5 samples. Tilt-series electron diffraction revealed that the μ -phase is a one-dimensional incommensurate structure, which can be described approximately as B-centered orthorhombic with a = 0.47 nm, b = 0.82 nm, and c = 3.86 nm.

The boron-content dependence of magnetic domain structures and magnetic properties of nanocrystalline Zr16Co82.5−x Mo1.5B x (x = 0, 1, 2, 3, 4) melt-spun ribbons have been investigated. Compared to x = 0, the smaller average domain size with a relatively short magnetic correlation length of 120 nm and largest root-mean-square phase shift value of 0.94° are observed for x = 1. The best magnetic properties of coercivity H c = 5.4 kOe, maximum energy product (BH) max = 4.1 MGOe, and saturation polarization J s = 7.8 kG, were obtained for the ribbon with x = 1. The optimal B addition enhances the content of hard magnetic phase, promotes magnetic domain structure refinement, and increases the surface roughness, results in the enhancement of magnetic anisotropy, and thus leads to a significant increase in coercivity and energy product in this sample.

The induced spin polarization of graphene on $\text{Cr}_{{2}}\text{O}_{{3}}$ (001) is investigated using density-functional theory (DFT) and model calculations. The magnetic moment in graphene is a proximity effect and can be regarded as a second-order Stoner scenario, and similar mechanisms are likely realized for all graphene systems with an insulating magnetic substrate. In the absence of charge transfer, the magnetic moment would be quadratic in the exchange field, as contrasted to the usually encountered approximately linear dependence. The net magnetization of the graphene is small, of the order of ${0.01}\ \mu_{\text{B}}$ per atom, but the energy-dependent spin polarization exhibits pronounced peaks that have a disproportionally strong effect on the spin-polarized electron transport and are therefore important for spin-electronics applications.

We report the formation of complex core–shell and three-layer Mn–Bi nanoparticles in a single step inert-gas condensation process. These structures have been achieved by controlling the thermal environment of the nanoparticles. High resolution transmission electron microscopy, high-angle annular dark-field imaging in scanning transmission electron microscopy mode, and elemental mapping by energy dispersive spectroscopy have been used to determine the crystal structure and chemical composition of the nanoparticles. These particles exist in two forms: (1) a crystalline Bi core with an amorphous Mn-rich shell, and (2) a crystalline Bi annular shell between two amorphous layers with high Mn concentration. These particles show significant magnetic hysteresis possibly arising from the change in bond length between Mn atoms introduced by Bi atoms in the bonding environment of the Mn atoms.

Structural, magnetic, and magnetocaloric properties of iron-deficient (Nd1−xCex)YFe17 alloys in the rhombohedral Th2Zn17–type crystal structure prepared by arc-melting and vacuum annealing have been investigated. Among the investigated alloys, (Nd0.7Ce0.3)YFe17 shows the highest values of magnetic entropy change and relative cooling power, namely 5.45 J kg−1 K−1 and 504 J kg−1 for a magnetic field change of 5 T. The Curie temperature and saturation magnetization of the (Nd0.7Ce0.3)YFe17 alloy are 301 K and 162 emu/g, respectively. The absence of thermal and magnetic hysteresis with relatively high cooling capacity near room temperature suggests that Fe-deficient (Nd0.7Ce0.3)YFe17 carries significant potential for room-temperature magnetic refrigeration.

The relationship between quantum mechanics and nanoscale spin dynamics is investigated by analyzing past work in magnetism and beyond. Findings about magnetization dynamics, accumulated throughout the 20th century, are revisited from a unifying modern perspective and related to trends in other areas of physics and technology. Traditional topics, for example spin precession and thermally activated magnetization processes, are discussed with emphasis on characteristic times and length scales, showing that nanoscale magnetization dynamics is very different from atomic spin dynamics. It is shown how these topics are connected to more recent developments such as the Berry phase, the no-cloning theorem, quantum-spin fluctuations, and THz magnetization dynamics in antiferromagnets.

Intermetallic compounds and micro-structures in Ni–Mn–In alloy system were investigated with transmission electron microscopy, selected-area and nano-beam electron diffraction, and energy-dispersive x-ray spectroscopy. Together with two types of Heusler phases, a decagonal quasicrystalline phase and a structurally related crystallite were found in the Ni–Mn–In system. As is well-known, most of the decagonal quasicrystals are aluminum-based intermetallic phases. It is interesting to investigate the aluminum-free decagonal quasicrystalline phase as a new member of the quasicrystal family. Structural characterization was carried out on the decagonal quasicrystalline phase and the crystalline approximant in the Ni–Mn–In alloy system.

Understanding of spin-gapless semiconductors with fully spin-polarized charge carriers is critically important because of their promise for spintronic applications. Here, we report non-collinear spin structures, magnetic ground state, and effective exchange interactions of the spin-gapless semiconductor CoFeCrAl investigated with noncollinear density functional calculations. The ground state of CoFeCrAl is ferrimagnetic and has a spin configuration with ↓ Fe, ↑ Co and ↑ Cr spins. In our constrained calculations, the magnetizations of the Fe, Co, and Cr sublattices are rotated by various angles θ, which give rise to three sets of noncollinear spin structures. For all three elements, the magnetic energy increases with the angle, which reconfirms the ferrimagnetic spin structure. During rotation, the magnitudes of the Co and Cr spins remain almost unchanged, whereas that of Fe strongly decreases as a function of the angle θ. This indicates that the finite-temperature behavior of CoFeCrAl is characterized by a pronounced non-Heisenberg behavior of the ↓ Fe moments, whereas the ↑ Co and ↑ Cr moments are Heisenberg-like. We discuss how this feature affects the finite-temperature behavior of the alloy beyond the commonly considered intersublattice Heisenberg exchange.