M-type strontium ferrite (SrFe12O19, SrM) is the base material for current commercial permanent magnets, and W-type strontium ferrite (SrFe18O27, SrW) is a candidate for next-generation high-magnetization ferrite magnets. Although SrM and SrW do not coexist in equilibrium in air, this study investigated the stability of their composite. Specifically, we examined the stability of X-type strontium ferrite (SrFe15O23, SrX), which has an intermediate composition between SrM and SrW, as well as the phase stability of the SrM/SrW mixture with the same chemical composition, as a function of oxygen partial pressure and temperature. In a reducing atmosphere in an open system with a controlled oxygen pressure ranging from 10−5 to 10−2 atm via gas flow rate, the SrM/SrW mixture was not in equilibrium. However, under vacuum in a closed tube, a pure SrM/SrW composite was successfully obtained. Furthermore, we discussed the phase relationships and transformations among the related phases from a thermodynamic point of view. We found that SrM and SrW coexist in the same crystal grain of the SrM/SrW composite and contact each other through a coherent interface. Based on these findings, we propose creating a type of exchange-spring magnet from SrM and SrW as a promising strategy for creating new, high-magnetization ferrite magnets.

Single-phase NiCo2O4 (NCO) nanoparticles (NPs) with an average particle size of 12 (+/- 3.5) nm were successfully synthesized as aggregates in urchin-like nanofibers via a hydrothermal route. Magnetization data measured as functions of temperature and magnetic field suggest a superparamagnetic-like behavior at room temperature, a ferrimagnetic transition around a Curie temperature T-C similar to 200 K, and a spin blocking transition at a blocking temperature T-B similar to 90 K, as observed at a field of 100 Oe. The spin blocking nature has been investigated by analyses of the field-dependence of T-B in the static magnetization and its frequency-dependence in the ac susceptibility data measured in zero-field cooling regime, both indicate a low-temperature spin glass-like state. Below T-B, the coercivity increases monotonically up to 1.7 kOe with decreasing temperature down to 5 K. Our results indicate that the magnetic behavior of NCO NPs, which is mainly determined by the cations' ratio, oxidation states, and site-occupancy, can be controlled by a synthesis in appropriate particle size and morphology.

ε ‐Iron carbide has garnered increasing interest for its superior magnetic characteristics and catalytic performance compared to other iron carbides. However, its metastable nature has posed significant challenges for synthesis, often requiring ultrahigh pressure, multistep processes, complex reaction condition control, and highly toxic reagents. Consequently, the properties of ε ‐iron carbide remain largely unexplored. A simplified synthesis method for ε ‐iron carbide can accelerate the exploration of new functionalities. In this study, a novel one‐step selective synthesis method for ε ‐iron carbide nanoparticles under mild conditions via a wet‐chemical approach is presented. In this method, Fe 3 (CO) 12 , cetyltrimethylammonium bromide (CTAB), and bis(pinacolato)diboron (B 2 pin 2 ) are added to hexadecylamine and reacted at 220 °C—a simple process that eliminates the need for extreme pressures and toxic substances. Detailed investigations elucidate the crucial roles of CTAB and B 2 pin 2 in facilitating the selective formation of ε ‐iron carbide. This accessible and efficient synthesis process for ε ‐iron carbide can further enable the discovery of unprecedented catalytic properties in the reductive amination of benzaldehyde, distinct from those of conventional iron nanoparticle catalysts. Density functional theory calculations reveal insights into the electronic states responsible for the distinct activity of the ε ‐iron carbide nanoparticles.

Some frustrated magnets exhibit a huge hysteresis called "global hysteresis (GH)", where the magnetic plateaus appearing in the increasing field process are skipped in the decreasing field process from the high magnetic field state. In this paper, we focused on the frustrated magnet DyRu2Si2 and measured magnetization relaxations from two plateau states inside the GH loop, the phases III and IV, and investigated the phase transitions into them. As a result of the relaxation measurements, no relaxation is observed in the phase III, whereas long-time relaxations of more than 105 s are observed at the phase IV plateau. Moreover, a Mpemba-effect-like relaxation phenomenon where the relaxation from an initial state prepared in the zero-field-cooled condition overtakes that from an initial state prepared in the field-cooled condition is observed. These results indicate that the phase IV is the non-ergodic state with a complex free-energy landscape with multiple local minima, while the phase III has a simple free energy structure. Therefore, the III-IV phase transition is considered to be the ergodic to non-ergodic phase transition. Although this type of phase transition typically occurs in random glassy systems, the phase IV in DyRu2Si2 has a regular long-range ordered magnetic structure and yet exhibits non-ergodic properties, which is highly nontrivial. Our findings open the possibility of observing non-ergodic states in frustrated magnets with regular long-range orders.

The Y-type ferrite Ba2Fe14O22 (Ba2Fe2+ 2 Fe3+ 12 O22) contains iron in a mixed valence state, which is expected to lead to intriguing physical properties arising from the interplay of charge, spin, and orbital degrees of freedom. In this paper, we present a comprehensive investigation of the temperature dependencies of the magnetic, electronic, and structural properties of high-quality polycrystalline Ba2Fe14O22. The material undergoes a ferrimagnetic transition at 662 K, followed by a sharp reduction in magnetization at 160 K. X-ray diffraction measurements revealed a first-order structural phase transition at 160 K, characterized by a symmetry change from rhombohedral to triclinic. Above this transition temperature, we observed a notable temperature dependence of magnetic anisotropy. The structural phase transition is attributed to the site-selective localization of Fe2+ cations, and the strong temperature dependence of magnetic anisotropy may be regarded as a precursor to the structural phase transition. Multiple frequency-dependent anomalies in AC susceptibility were observed, which may be linked to the motion of magnetic domain walls. While extrinsic, these dynamics reflect the effect of Fe cation degrees of freedom within this system.

We successfully synthesized single crystals of a series of C15b Laves-phase compounds, RInCo4 (R = Dy-Tm), with Co-pyrochlore and R-fcc sublattices, and systematically studied their magnetic properties via magnetometry measurements. These itinerant cubic compounds, with Curie temperatures above room temperature, show compensated ferrimagnetism featuring an antiferromagnetic coupling between the two sublattices. From this series, DyInCo4 exhibits the highest TC (=368 K) and a near-room-temperature compensation point Tcp (=295 K). TC does not change drastically with the R atom, whereas Tcp is dependent. Another magnetization anomaly is observed in all the compounds at low temperatures, which may be indicative of changes in the lattice or magnetic structure. The easy axis of the ferrimagnetic moment of DyInCo4, ErInCo4, and TmInCo4 is proposed at T = 5 K to be along the [001], [111], and [110] directions, respectively. However, the simple easy-axis or easy-plane ferrimagnetic picture cannot be applied to HoInCo4. These observations suggest that the R sublattice determines magnetic anisotropy and compensation, while the Co sublattice plays a role in strong magnetic ordering. The high Curie temperature, together with the magnetization compensation point near room temperature, renders these itinerant pyrochlore magnets interesting for spintronic applications.

The La-Co co-substituted magnetoplumbite-type (M-type) ferrites AFe(12)O(19) (A = Ca, Sr and Ba, ion sizes Ca2+< Sr2+< Ba2+) with Co compositions around 0.2 have been subjected to Co-59-NMR. The results show that Co occupies the 4f(1), 2a and 12k sites, and that the smaller the A ion, the more Co tends to occupy the 4f(1) minority spin site, which is effective in enhancing both uniaxial anisotropy and magnetisation. First-principles total energy calculations based on density functional theory (DFT) of undoped AFe(12)O(19) and a supercell (2x2x1 of the unit cell) in which 1/96 of Fe3+ is replaced by Co2+ were performed to predict the stable structure and Co occupancy sites. The results show that regardless of A, Co is most stable when it occupies the 4f(1) site, followed by the 2a and 12k sites with energy differences on the order of 100 meV, and Co practically does not occupy the 2b and 4f(2) sites. As the A ion becomes smaller, the energy difference when Co occupies each Fe site tends to increase, and the Co occupancy of the 4f(1) site also increases. The site selectivity of Co can be roughly explained as a result of the difference in uniaxial strain along the c-axis associated with the difference in A. However, the influence of the A ion differs between the R and S blocks and the local strain also has a secondary effect on the Co distribution. Based on these results, the guidelines for improving the performance (anisotropy and magnetisation) of La-Co co-substituted M-type ferrite magnets with a limited amount of Co can be summarised as follows: It is effective to select as small A ions as possible and to post-anneal at low temperature or cool slowly to concentrate Co at the 4f(1) site in tetrahedral coordination.

ScFe6Ge4 with the LiFe6Ge4-type structure (space group R3m), which has a double -layered kagome lattice (18h site) of Fe crystallographically equivalent to that of a well-known topological ferromagnet Fe3Sn2, is newly found to be antiferromagnetic (AFM) with a high Neel temperature of TN approximate to 650 K, in contrast to the ferromagnetic (FM) ground state previously proposed in a literature. 45Sc nuclear magnetic resonance experiment revealed the absence of a hyperfine field at the Sc site, providing microscopic evidence for the AFM state and indicating AFM coupling between the bilayer kagome blocks. The stability of the AFM structure under the assumption of FM intra-bilayer coupling is verified by DFT calculations.

Complexity of quantum phases of matter is often understood theoretically by using gauge structures, as is recognized by the ℤ_2 and U(1) gauge theory description of spin liquids in frustrated magnets. Anomalous Hall effect of conducting electrons can intrinsically arise from a U(1) gauge expressing the spatial modulation of ferromagnetic moments or from an SU(2) gauge representing the spin-orbit coupling effect. Similarly, in insulating ferro and antiferromagnets, the magnon contribution to anomalous transports is explained in terms of U(1) and SU(2) fluxes present in the ordered magnetic structure. Here, we report thermal Hall measurements of MnSc 2 S 4 in an applied field up to 14 T, for which we consider an emergent higher rank SU(3) flux, controlling the magnon transport. The thermal Hall coefficient takes a substantial value when the material enters a three-sublattice antiferromagnetic skyrmion phase, which is in agreement with the linear spin-wave theory. In our description, magnons are dressed with SU(3) gauge field, which is a mixture of three species of U(1) gauge fields originating from the slowly varying magnetic moments on these sublattices.

NiCr2O4nanoparticles with average particle size ∼15 nm, a single-domain size maintains the bulk canted antiferromagnetic ground state, were synthesized by a microwave combustion method. The magnetic behavior was carefully investigated by static and dynamic magnetic susceptibility measurements. In addition to a spin-glass-like behavior below paramagnetic-ferrimagnetic transition atTC, the NiCr2O4nanoparticles demonstrate a low-temperature cluster spin glass transition below the spin canting transitionTS, which manifests itself as a magnetic anomaly peak around ∼12 K (at 100 Oe) in the zero-field cooled magnetization with a relatively stronger field dependence in a 'de Almeida-Thouless' line for spin glasses. The AC susceptibility analyses in different approaches demonstrate a larger relative peak temperature variation per frequency decade and a longer characteristic relaxation time in the order of 0.04 and 10-7s, against 0.01 and 10-9s for the high-temperature blocking, indicating the slow spin dynamics for the low-temperature cluster glassy phase. A field-temperature magnetic phase diagram is proposed for the single-domain NiCr2O4nanoparticles.

Molybdenum(VI) oxide (MoO3) is a promising semiconductor material that can be used in several functional applications. Understanding the structural response of MoO3 under high-pressure and high-temperature conditions is important for designing a material used in device applications. An X-ray free electron laser (XFEL) enables the structural response under extreme conditions to be probed at the nanosecond timescale. We describe laser-driven shock compression experiments on MoO3 using an XFEL to directly observe the structural evolution of MoO3. When a laser-driven shock wave arrives at a pressure of 61 GPa, MoO3 melts immediately and remains in the molten state for a few nanoseconds. Rapid recrystallization to the α-MoO3 phase and a high-pressure phase MoO3-II is also observed on nanosecond timescales during pressure release. Our results provide insights into the kinetic and phase transition under shock compression and represent the advancement toward the understanding structural response of MoO3 under high-pressure, high-temperature conditions, which has not been studied.

AbstractThe kagome lattice is an intriguing and rich platform for discovering, tuning and understanding the diverse phases of quantum matter, crucial for advancing modern and future electronics. Despite considerable efforts, accessing correlated phases at room temperature has been challenging. Using single-crystal X-ray diffraction, we discovered charge order above room temperature in La(Ru1−xFex)3Si2(x= 0, 0.01, 0.05), where charge order related to out-of-plane Ru atom displacements appears belowTCO,I ≃ 400 K. The secondary charge ordered phase emerges belowTCO,II ≃ 80–170 K. Furthermore, first principles calculations reveal both the kagome flat band and the van Hove point near the Fermi energy in LaRu3Si2, driven by Ru-dz2orbitals. Our results identify LaRu3Si2as the kagome superconductor with the highest known charge ordering temperature, offering a promising avenue for researching room temperature quantum phases and developing related technologies.

We have successfully synthesized single crystals of the site-ordered cubic (C15b) Laves phase compound LuInCo4 with the Co-pyrochlore sublattice. LuInCo4 undergoes a ferromagnetic transition at 306 K and has a saturation moment of 3.43 mu B/f.u. at 5 K. The strongly ferromagnetic nature was verified by density functional theory calculations, suggesting that Co-3d flat bands near the Fermi level induce the spin polarization. The magnetization is isotropic above approximate to 100 K, and saturates most easily in the [100] direction at low temperatures. In this anisotropic ferromagnetic state, the magnetization undergoes a metamagnetic transition in the [111] direction. Our results suggest that LuInCo4 is a strong but unusual itinerant electron ferromagnet, which deserves further study as a pyrochlore metal.

Nonlinear optical materials of atomic thickness, such as non-centrosymmetric 2H transition metal dichalcogenide monolayers, have a second-order nonlinear susceptibility (χ(2)) whose intensity can be tuned by strain. However, whether χ(2) is enhanced or reduced by tensile strain is a subject of conflicting reports. Here, we grow high-quality MoSe2 monolayers under controlled biaxial strain created by two different substrates and study their linear and nonlinear optical responses with a combination of experimental and theoretical approaches. Up to a 15-fold overall enhancement in second-harmonic generation (SHG) intensity is observed from MoSe2 monolayers grown on SiO2 when compared to its value on a Si3N4 substrate. By considering an interference contribution from different dielectrics and their thicknesses, a factor of 2 enhancement of χ(2) was attributed to the biaxial strain: substrate interference and strain are independent handles to engineer the SHG strength of non-centrosymmetric 2D materials.

We investigated the effect of post-annealing on the magnetic anisotropy in La– Co co-substituted magnetoplubite-type strontium ferrite, a matrix phase of commercial high-performance ferrite magnets. Post-annealing was found to be effective in controlling the distribution of substituted Co2+. The Co2+ distribution obtained by lower-temperature annealing shows higher magnetic anisotropy, suggesting that uniaxial magnetic anisotropy is enhanced only when Co2+ occupies the most stable occupied site, i.e., the 4f1 site in the tetrahedral coordination. Furthermore, the slower the cooling rate, the higher the anisotropy. The temperature-dependent Co2+ distribution predicted from the reported density functional theory calculations was compared with the actual anisotropy after annealing, yielding +2.3 meV/ion as the Co2+ anisotropy constant at the tetrahedrally coordinated site and −1.2 meV/ion as that at the octahedrally coordinated sites. Careful selection of heat treatment conditions leads to efficient use of cobalt, an element with supply risks.

We have succeeded for the first time in synthesizing single crystals of nanolaminated borides (Fe_1-xMn_x)_2AlB_2 in the entire Fe-Mn composition range using the Al self-flux method, and have established T-x, H-T and three-dimensional H-T-x magnetic phase diagrams from the results of magnetization measurements. The ferromagnetic correlation of Fe_2AlB_2 is weakened with the Mn substitution, whereas the antiferromagnetic correlation of Mn_2AlB_2 is enhanced with the Fe up to x=0.65. The spin direction in the magnetic ordered states changes from the a to the b axis with increasing Mn concentration and temperature. At x = 0.31-0.46, there are three magnetic phases; ferromagnetic, antiferromganetic, and intermediate phases in between. At x = 0.65 and 0.74, a spin-flop-like metamagnetic transition was observed at a finite field parallel to the spin direction. These observations indicate that in (Fe_1-xMn_x)_2AlB_2 the ferromagnetic and antiferromagnetic correlations coexist and the uniaxial magnetic anisotropy competes between the a and b axes.

The kagome lattice has emerged as a promising platform for hosting unconventional chiral charge order at high temperatures. Notably, in LaRu$_{3}$Si$_{2}$, a room-temperature charge-ordered state with a propagation vector of ($\frac{1}{4}$,~0,~0) has been recently identified. However, understanding the interplay between this charge order and superconductivity, particularly with respect to time-reversal-symmetry breaking, remains elusive. In this study, we employ single crystal X-ray diffraction, magnetotransport, and muon-spin rotation experiments to investigate the charge order and its electronic and magnetic responses in LaRu$_{3}$Si$_{2}$ across a wide temperature range down to the superconducting state. Our findings reveal the emergence of a charge order with a propagation vector of ($\frac{1}{6}$,~0,~0) below $T_{\rm CO,2}$ ${\simeq}$ 80 K, coexisting with the previously identified room-temperature primary charge order ($\frac{1}{4}$,~0,~0). The primary charge-ordered state exhibits zero magnetoresistance. In contrast, the appearance of the secondary charge order at $T_{\rm CO,2}$ is accompanied by a notable magnetoresistance response and a pronounced temperature-dependent Hall effect, which experiences a sign reversal, switching from positive to negative below $T^{*}$ ${\simeq}$ 35 K. Intriguingly, we observe an enhancement in the internal field width sensed by the muon ensemble below $T^{*}$ ${\simeq}$ 35 K. Moreover, the muon spin relaxation rate exhibits a substantial increase upon the application of an external magnetic field below $T_{\rm CO,2}$ ${\simeq}$ 80 K. Our results highlight the coexistence of two distinct types of charge order in LaRu$_{3}$Si$_{2}$ within the correlated kagome lattice, namely a non-magnetic charge order ($\frac{1}{4}$,~0,~0) below $T_{\rm co,1}$ ${\simeq}$ 400 K and a time-reversal-symmetry-breaking charge order below $T_{\rm CO,2}$.