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The realization of spin-glass (S-G) state in Heusler alloys is very rare despite the presence of inherent structural and elemental disorder in those compounds. Although a few half and full Heusler alloys are known to exhibit S-G state, there is hardly any manifestation of the same in cases of quaternary Heusler compounds. Here we report the observation of S-G state in a highly disordered equiatomic quaternary Heusler compound: FeRuMnGa, where the S-G state is in between of canonical S-G and cluster glass. Different intricate features of S-G state including non-equilibrium magnetic dynamics at low temperature in the compound are unveiled through our comprehensive magnetic, heat capacity and neutron diffraction studies. The structural disorder in the sample is neither conventional \textit{A2}- nor \textit{B2}-type while those two types are commonly observed for Heusler compounds. The presence of disorder also plays a significant role in electron transport properties of the alloy, which is reflected in its exhibition of semi-metallic behavior and anomalous Hall effect at low temperature., Comment: 11 pages, 13 figures

Tuning the chemistry of materials often leads to discoveries of interesting phenomena that expand basic science and support practical applications. Here we show how different spin–orbit coupling in light and heavy lanthanides can be exploited to create complex magnetic ground states and thereby unusual spontaneous exchange bias (SEB), conventional exchange bias (CEB), and magnetic memory effects in almost ideally magnetically compensated Pr0.75Gd0.25ScGe, which is a representative of the PrScGe–GdScGe solid solution. We report the synthesis and detailed characterization of Pr0.75Gd0.25ScGe by X-ray powder diffraction, scanning electron microscopy, and magnetization measurements in magnetic fields up to 140 kOe. Partial substitution of a light lanthanide, Pr, with a heavy lanthanide, Gd, results in a complex magnetic ground state, which includes large spontaneous and conventional exchange biases reaching magnitudes of ∼1.7 kOe and ∼3.5 kOe, respectively, at T = 2 K, as well as shape dependent magnetic compensation and bias phenomena occurring in small external fields.

An innovative method of synthesis is reported for the large and diverse (RE)6(TM)x(Tt)2S14 (RE = rare-earth, TM = transition metals, Tt = Si, Ge, and Sn) family of compounds (∼1000 members, ∼325 contain Si), crystallizing in the noncentrosymmetric, chiral, and polar P63 space group. Traditional synthesis of such phases involves the annealing of elements or binary sulfides at elevated temperatures. The atomic mixing of refractory components technique, presented here, allows the synthesis of known members and vastly expands the family to nearly the entire transition metal block, including 3d, 4d, and 5d TMs with oxidation states ranging from 1+ to 4+. Arc-melting of the RE, TM, and tetrel elements of choice forms an atomically-mixed precursor, which readily reacts with sulfur providing bulk powders and large single crystals of the target quaternary sulfides. Detailed in situ and ex situ experiments show the mechanism of formation, which involves multiphase binary sulfide intermediates. Crystal structures and metal oxidation states were corroborated by a combination of single crystal X-ray diffraction, elemental analysis, EPR, NMR, and SQUID magnetometry. The potential of La6(TM)x(Tt)2S14 compounds for non-linear optical applications was also demonstrated., Synthesis from atomically-mixed precursors opens up a phase space to hundreds of chiral and polar sulfide semiconductors with almost any transition metal in variable oxidation states.

We employ a descriptor based machine-learning approach to assess the effect of chemical alloying on formation-enthalpy of rare-earth intermetallics. Application of machine-learning approaches in rare-earth intermetallic design have been sparse due to limited availability of reliable datasets. In this work, we developed an `in-house' rare-earth database with more than 600$+$ compounds, each entry was populated with formation enthalpy and related atomic features using high-throughput density-functional theory (DFT). The SISSO (sure independence screening and sparsifying operator) based machine-learning method with meaningful atomic features was used for training and testing the formation enthalpies of rare earth compounds. The complex lattice function coupled with the machine-learning model was used to explore the effect of transition metal alloying on the energy stability of Ce based cubic Laves phases (MgCu$_{2}$ type). The SISSO predictions show good agreement with high-fidelity DFT calculations and X$-$ray powder diffraction measurements. Our study provides quantitative guidance for compositional considerations within a machine-learning model and discovering new metastable materials. The electronic-structure of Ce$-$Fe$-$Cu based compound was also analyzed in$-$depth to understand the electronic origin of phase stability. The interpretable analytical models in combination with density$-$functional theory and experiments provide a fast and reliable design guide for discovering technologically useful materials., 19 pages, 9 figures

Three-dimensional heterostructures are usually created either by assembling two-dimensional building blocks into hierarchical architectures or using stepwise chemical processes that sequentially deposit individual monolayers. Both approaches suffer from a number of issues, including lack of suitable precursors, limited reproducibility, and poor scalability of the preparation protocols. Therefore, development of alternative methods that enable preparation of heterostructured materials is desired. We create heterostructures with incommensurate arrangements of well-defined building blocks using a synthetic approach that comprises mechanical disassembly and simultaneous reordering of layered transition-metal dichalcogenides, MX2, and non-layered monochalcogenides, REX, where M = Ta, Nb, RE = Sm, La, and X = S, Se. We show that the discovered solid-state processes are rooted in stochastic mechanochemical transformations directed by electronic interaction between chemically and structurally dissimilar solids toward atomic-scale ordering, and offer an alternative to conventional heterostructuring. Details of composition–structure–properties relationships in the studied materials are also highlighted., 3D heterostructures offer properties that are inaccessible in bulk single-phase solids, but synthetic approaches are limited. The authors use mechanochemical reshuffling of binary precursors and subsequent annealing to design structurally aligned misfit heterostructures with well-defined atomic arrangements.

Chemical substitution is one of the most efficient tools to tune and optimize magnetic and magnetocaloric properties of the giant magnetocaloric materials. In particular, Indium substitutions could be useful both for tuning properties of these interesting intermetallic materials and to unveil their local-scale behavior across the magnetostructural transition via hyperfine techniques. Hence, in order to investigate the effect of Indium additions on the crystal structure, micro-structure, magnetic and magnetocaloric properties, a series of In-containing samples derived from the base Gd5Si1.2Ge2.8 stoichiometry were prepared. The major findings are that while In is insoluble in the 5: 4 phase, it will instead promote the emergence of the impurity 5: 3 phase and segregates into this phase. Hence, In leads to major crystallographic changes, which enhance atomic disorder and disrupt the Si to Ge ratio in the 5: 4 phase. Subsequently, a higher 5: 4 unit cell volume and a lower magnetic ordering temperature are found in the In-substituted samples. Finally, the magnetocaloric properties of the In-substituted samples reveal a detrimental effect on the maximum magnetic entropy change., Work is partially supported by the projects POCI/CTM/61284/2004, PTDC/CTM-NAN/115125/2009, FEDER/POCTI n0155/94 from Fundacão para a Ciência ex Tecnologia (FCT), Portugal. A.M.P. thanks FCT for the Grant No. SFRH/BPD/63150/2009. J H Belo thanks FCT for the Grant SFRH/BD/88440/2012, the project PTDC/FISMAC/ 31302/2017 and his contract DL57/2016 reference SFRH-BPD-87430/2012. Work at IFIMUP is supported by the following funding projects: POCI-01-0145-FEDER-032527, POCI-01–0145-FEDER-029454 and CERN-FIS-PAR-0005-2017. Work at the INMA is supported by the Spanish Ministerio de Ciencia, Innovacion y Universidades through project MAT2017-82970-C2, PID2020-112914RB-I00 and Spanish DGA (grant no. E28−20R). The research at Ames Laboratory is supported by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences of the U.S. Department of Energy (DOE). Ames Laboratory is operated for the U.S DOE by Iowa State University under Contract No. DE-AC02-07CH11358.

The coupling between structural and magnetic degrees of freedom is crucial for realization of interesting physical phenomena associated with magneto-structural transformations resembling austenite-to-martensite transitions. Despite substantial efforts in design and discovery of materials with strong magnetocaloric effects, a majority of viable candidates are composed of non-earth-abundant and toxic elements, while others involve challenging syntheses and post processing. Guided by advanced density functional theory calculations, we report a new family of compounds, i.e., Mn0.5Fe0.5NiSi1-xAlx [x = 0.045–0.07] exhibiting a giant magnetocaloric effect (MCE) that is tunable near room temperature. Their MCE functionality arises from a distinct magneto-structural transformation between a paramagnetic hexagonal Ni2In-type phase and ferromagnetic orthorhombic TiNiSi-type phase that can be actuated by magnetic field and/or pressure. As the transition is sensitive to external hydrostatic pressure, the same materials should also exhibit a strong barocaloric response in addition to the giant MCE.

Magnetocaloric refrigeration is a solid-state cooling approach that promises high energy efficiency and low environmental impact. It remains uncompetitive with conventional vapor-compression technologies due to lack of high-performing materials that exhibit large magnetocaloric effects in low magnetic fields. Here we report a game-changing enhancement of the magnetocaloric response in a transition-metal-based Ni–Co–Mn–Ti. Mechanically and chemically stable rapidly solidified ribbons exhibit magnetic entropy changes as high as ∼ 27 J⋅kg−1K−1 for a moderate field change of 2 T, comparable to or larger than the best known materials for near-room temperature applications. The ribbons can be easily manufactured in large quantities and the transition temperature can be adjusted by varying Co concentration.

The kinetic arrest observed in the parent Gd5Ge4 gradually vanishes when a small fraction (x = 0.025, 0.05 and 0.10) of Gd is replaced by Sc in (Gd1−xScx)5Ge4, and the magnetic ground state changes from antiferromagnetic (AFM) to ferromagnetic (FM). A first order phase transition coupled with the FM-AFM transition occurs at TC = 41 K for x = 0.05 and at TC = 53 K for x = 0.10 during heating in applied magnetic field of 1 kOe, and the thermal hysteresis is near 10 K. The first-order magnetic transition is coupled with the structural Sm5Ge4-type to Gd5Si4-type transformation. The magnetization measured as a function of applied magnetic field shows sharp metamagnetic-like behavior. At the same time, the AFM to paramagnetic transition in (Gd1−xScx)5Ge4 with x = 0.10, is uncharacteristically broad indicating development of strong short-range AFM correlations above the Neel temperature. Comparison of the magnetization data of bulk, powdered, and metal-varnish composite samples of (Gd0.95Sc0.05)5Ge4 shows that mechanical grinding and fabrication of a composite have little effect on the temperature of the first-order transformation, but short-range ordering and AFM/FM ratio below TC are surprisingly strongly affected.

The magnetic and magnetocaloric properties of DyCo2Cx (x = 0, 0.05, 0.1, and 0.15) alloys were investigated. The results show that the Curie temperature (TC) of the DyCo2Cx alloys increases with increasing C content, from 136 K (x = 0) to 152 K (x = 0.15), but the lattice parameter a of DyCo2Cx exhibits a maximum at x = 0.05. The suppression of the ac susceptibility of DyCo2Cx at low temperature indicates the enhancement of the domain wall pinning effect by carbon doping. The positive slops of the Arrott plots of the doped compounds indicate that the phase transition is second order for the carbon-doped alloys, and the maximum value of the isothermal magnetic entropy change (ΔSM) for the magnetic field change of 50 kOe decreases from −13.9 J/kg· K (x = 0) to −7.8 J/kg·K (x = 0.15). The relative cooling power (RCP) of DyCo2Cx is nearly the same in all studied alloys, while the temperature-averaged entropy change over 10 K temperature span, TEC(10), indicates decreasing magnetocaloric performance of carbon doped materials.

Magnetic ionic liquids (MILs) are a subclass of ionic liquids that possess a paramagnetic metal within their chemical structure, making them susceptible to external magnetic fields. A total of twenty-four (24) MILs were prepared and characterized to investigate the effect of the ligand, cation and anion on the physiochemical properties of acetylacetonate-based MILs. It was found that thermal stabilities as high as 260 °C could be achieved by incorporating aromatic moieties in the anion structure. Additionally, the magnetic moment could be modulated by simply changing the transition metal in the anion. Magnetic moment values of 2.8 μB, 4.5 μB and 5.6 μB were obtained by using Ni(II), Co(II), and Mn(II) as the metal centers, respectively. Furthermore, the viscosity of the MILs could be tailored from a few hundred centipoise to several thousand centipoise, increasing their potential applications in numerous interdisciplinary fields. Moreover, the MILs synthesized in this study were found to be insoluble in water at a MIL-to-solvent ratio of 0.01% (w/v), making them potentially useful in targeted separations, where very hydrophobic solvents are highly desired.

Magnetic and magnetocaloric properties of H o 1 - x D y x A l 2 compounds with x = 0 , 0.05 , 0.10 , 0.15 , 0.25 and 0.50 , modelled using a Hamiltonian that includes the exchange interactions between Ho-Dy, Ho-Ho and Dy-Dy ions in addition to the crystalline electric field and the Zeeman effects, have been compared with those determined experimentally. In order to reproduce experimentally observed global ferromagnetic ordering temperatures and spin reorientation transition temperatures as xDy varies, the exchange interactions between Ho-Dy and Ho-Ho were set as free parameters and adjusted to match the experimental results. We demonstrate that heat capacity of polycrystalline materials in non-zero magnetic fields can be satisfactory reproduced by using the average of multiple magnetic field directions with respect to the crystallographic coordinate system, while reasonably good agreement between experimentally determined and theoretically predicted magnetocaloric effects can be achieved considering an average of only three field directions.

Binary intermetallic ${\mathrm{Eu}}_{2}\mathrm{In}$ was recently reported to exhibit a giant anhysteretic magnetocaloric effect due to a first-order magnetic phase transition between paramagnetic and ferromagnetic states. Experimentally, the transition occurs with a small phase volume change, $\mathrm{\ensuremath{\Delta}}V/V$, of approximately 0.1% around ${T}_{C}$ of $ca.$ 55 K. We represent magnetic and compute magnetocaloric properties of a ${\mathrm{Eu}}_{2}\mathrm{In}$ compound using a microscopic description based on a model Hamiltonian that takes into account magnetic exchange and magnetoelastic interactions. In the model the thermodynamic nature of the transition is conveniently represented by a single magnetoelastic interaction parameter. A good agreement between the theoretical results and earlier published experimental data confirms the effectiveness of our approach.

While binary $R{E}_{2}\mathrm{In}$, where $RE=\mathrm{rare}\phantom{\rule{0.16em}{0ex}}\mathrm{earth}$, have been reported a few decades ago, recent investigations revealed intriguing new physical insights. For instance, the discovery of a nearly ideal first-order ferromagnetic transition in ${\mathrm{Eu}}_{2}\mathrm{In}$ calls for further exploration of structures and properties of $R{E}_{2}\mathrm{In}$, in particular for the least-documented $RE=\mathrm{Eu}$ and Yb cases. Here, we investigate ${\mathrm{Eu}}_{2\text{\ensuremath{-}}x}{\mathrm{Yb}}_{x}\mathrm{In}$ pseudobinaries with nominal values of $x=0.25$, 0.5, 0.75, 1, 1.5, 2 by powder x-ray diffraction (including as function of temperature from 100 to 375 K for ${\mathrm{Yb}}_{2}\mathrm{In}$), magnetization (5--300 K), as well as electrical resistivity (5--300 K) and calorimetric (2--150 K) measurements for ${\mathrm{Yb}}_{2}\mathrm{In}$. Compared to other RE, Yb or Eu always raise challenging questions linked to their valence states. From average atomic volume, Yb is anticipated to be divalent in ${\mathrm{Yb}}_{2}\mathrm{In}$, at least between 100 and 375 K, which is in line with the absence of $4f$ magnetism. In agreement with x-ray diffraction and magnetization data, the resistivity of ${\mathrm{Yb}}_{2}\mathrm{In}$ is rather featureless and typical of a metal. Establishing ${\mathrm{Yb}}_{2}\mathrm{In}$ as a nonmagnetic isostructural reference for ${\mathrm{Eu}}_{2}\mathrm{In}$ allows one to use its heat capacity to revisit that of the latter, and get experimental insights into the exceptional magnetocaloric effect of the compound with Eu. In particular, we show that a third of the total magnetic entropy (${S}_{\mathrm{m}}\ensuremath{\approx}35.6\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}\mathrm{mo}{\mathrm{l}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at $T=100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) is concentrated in a 3 K temperature window around the ${T}_{\mathrm{C}}$ of ${\mathrm{Eu}}_{2}\mathrm{In}$. Starting from the ferromagnetic compound ${\mathrm{Eu}}_{2}\mathrm{In}$ $[{T}_{\mathrm{C}}=55.2(5)\phantom{\rule{0.16em}{0ex}}\mathrm{K}]$, we show that Yb substitutions in ${\mathrm{Eu}}_{2\text{\ensuremath{-}}x}{\mathrm{Yb}}_{x}\mathrm{In}$ lead to a decrease in both the Curie temperature [${T}_{\mathrm{C}}=41(2)$ and 32(2) K for $x=0.25$ and 0.5] and magnetic saturation, while weakening the first-order character of the transition as $x$ increases. A significant isothermal entropy change of $5.1(4)\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}\mathrm{mo}{\mathrm{l}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ for $\mathrm{\ensuremath{\Delta}}B=2\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ is found at 44 K in ${\mathrm{Eu}}_{1.75}{\mathrm{Yb}}_{0.25}\mathrm{In}$, demonstrating that the giant magnetocaloric effect of ${\mathrm{Eu}}_{2}\mathrm{In}$ can be tuned to lower temperatures by Yb substitutions.

Using first-principles calculations, based on disordered local moment (DLM) theory combined with the self-interaction corrected local spin density approximation (SIC-LSDA), we study magnetic correlations in the paramagnetic state of $\mathrm{Gd}X\phantom{\rule{4pt}{0ex}}(X$=Cu, Zn, Ga, Ag, Cd, In, Au, Hg, and Tl) intermetallics and their alloys. The predicted magnetic orders and ordering temperatures that these correlations lead to are in overall good agreement with available experiments. The interactions between the Gd $f$-electron local moments are mediated by the valence electrons of the intermetallics which comprise both Gd and $X\phantom{\rule{4pt}{0ex}}d$ bands as well as $sp$ bands. There are RKKY-like features such as dependence on the number of $sp$-valence electrons but other variations manifest themselves in the phase diagrams as regions of incommensurate magnetic ordering, the origin and range of which are related to the binding energies of the alloying anion $d$ states, and their propensity to hybridize with the Gd states at the Fermi level.

Conventional magnetometry is irreplaceable in evaluating bulk magnetization of materials over broad temperature and field ranges. The technique is also effective in quantifying hysteresis that may be associated with magnetic and structural phase transitions that occur during the magnetizing/demagnetizing cycling, and the derived magnetic field-induced isothermal entropy change – one of the most important properties in the field of magnetocalorics. Both systematic and random errors present during the measurements of magnetization, however, may lead to erroneous conclusions. Using two well-known materials – elemental Gd and intermetallic Gd5Si2Ge2 as examples, we consider best practices in performing reliable and rapid magnetization measurements for proper characterization of magnetocaloric properties.

Future advancements in magnetocaloric refrigeration/heat pumping technologies depend on the discovery of new materials that demonstrate large, tunable magnetocaloric effects (MCEs) in the vicinity of coupled magnetic and structural phase transitions that occur reversibly with minimum hysteresis. With this in mind, we investigate phase transitions, microstructure, magnetic, thermal, magnetocaloric, and transport properties of (Gd5-xScx)Si1.8Ge2.2 compounds. Replacement of magnetic Gd with non-magnetic Sc in Gd5-xScxSi1.8Ge2.2 increases the ferromagnetic to paramagnetic first order phase transition temperature, TC, with only a minor reduction in MCE when x ≤ 0.2. We also demonstrate that hydrostatic pressure further increases TC and reduces the hysteresis of the first order phase transition in Gd4.8Sc0.2Si1.8Ge2.2 from 7 to 4 K. Temperature-dependent x-ray powder diffraction study of Gd4.8Sc0.2Si1.8Ge2.2 confirms the monoclinic ↔ orthorhombic structural transformation at TC, in agreement with magnetic, calorimetric, and electrical transport measurements. In addition to the substantial magnetocaloric effect, a large magnetoresistance of ∼20% is also observed in Gd4.8Sc0.2Si1.8Ge2.2 for ΔH = 50 kOe in the vicinity of the magnetostructural transition. In a drastic reversal of the initial doping behavior further additions of Sc (x > 0.2) suppress formation of the monoclinic phase, change the nature of the transition from first-to second-order, and reduce both the transition temperature and magnetocaloric effect.

Using first-principles calculations, based on disordered local moment theory, combined with the self-interaction corrected local spin density approximation, we study magnetic interactions in GdX intermetallics for X = Cu, Zn, Ga, Cd, and Mg. Our predicted magnetic orders and ordering temperatures both at zero and other pressures agree well with experiments including the large increase in the Curie temperature of GdCd under pressure that is shown by our own experimental measurements. From our results it emerges that the Ruderman-Kittel-Kasuya-Yosida interaction on its own can not explain the observed behaviour under pressure, and that the magnetic ordering mechanism is strongly influenced by the occupations of both Gd and anion d -bands.

Three series of intermetallic compounds Eu(T1,T2)5In (T = Cu, Ag, Au) have been investigated over their full compositional ranges. Single crystals of all compounds have been obtained by self-flux and were analyzed by single crystal X-ray diffraction revealing that the representatives fall into two structure types: CeCu6 (oP28, Pnma, a = 8.832(3)–9.121(2) A, b = 5.306(2)–5.645(1) A, c = 11.059(4)–11.437(3) A, V = 518.3(3)–588.9(2) A3) and YbMo2Al4 (tI14, I4/mmm, a = 7.139(2)–7.199(2) A, c = 5.417(3)–5.508(1) A, V = 276.1(2)–285.8(1) A3). The structural preference was found to depend on the cation/anion size ratio, while the positional preference within the CeCu6 type structure shows an apparent correlation with the anion size. Chemical compression, hence, a change in cell volume, which occurs upon anion substitution, appears to be the main driving force for the change of magnetic ordering. While EuAg5In shows antiferromagnetic behavior at low temperatures, mixing Cu and Au within the same type of structure results in considerable changes in the magnetism. The Eu(Cu,Au)5In alloys with CeCu6 structure show complex magnetic behaviors and a strong magnetic field-induced spin-reorientation transition with the critical field of the transition being dependent on Cu/Au ratio. The alloys adopting the YbMo2Al4 type structure are ferromagnets exhibiting unusually high magnetic moments. The heat capacity of EuAu2.66Cu2.34In reveals a double-peak structure evolving with the magnetic field. However, low-temperature X-ray powder diffraction does not show a structural transition.

The magnetic properties of β-Ce at low temperature have been studied through ac susceptibility measurements under hydrostatic He-gas pressure up to 4.5 kbar. The Neel temperature, TN = 12.7 K at 58 bar, initially increases with pressure at the rate dTN/dP = +0.32 ± 0.05 K/kbar. After releasing pressure from 4.5 to 0.06 kbar at 40 K, the magnetic susceptibility anomaly associated with the antiferromagnetic transition is markedly reduced. Surprisingly, TN also shifts from 12.7 to 14 K. Both effects likely arise from an irreversible β → α transition under pressure.

The thermal evolution of lattice parameters coupled with heat capacity data provide insight into tailorable magnetism-structure attributes in the orthorhombic compound AlFe2B2 that was synthesized with and without small additions of gallium. Temperature-dependent X-ray powder diffraction experiments conducted through the magnetic phase transition reveal that the a- and b-parameters of both samples increase with increasing temperature while the c-parameter decreases. While a weak volumetric thermal expansion is noted over a range of temperatures well below and above the magnetic phase transition, anomalous behavior was observed within the phase transition region itself to reveal a magnetostructural phase transition with borderline first-order character in the Ga-modified sample but of more second-order character in the Ga-free sample. It is established that the nearest-neighbor Fe-Fe interatomic distance within the (ab)-plane plays a dominant role in influencing the magneto-functional response of these compounds. The magnetocaloric properties are discussed in the context of temperature-induced changes of the interatomic bonding that are influenced by the hypothesized presence of iron antisite defects in the AlFe2B2 lattice.

The intrinsic magnetic properties of the La0.9Nd0.1Fe12B6 compound have been studied by magnetization measurements. The compound orders ferromagnetically (FM) at the Curie temperature, TC, of ~58 K, which shifts toward higher temperatures with increasing magnetic field. At 2 K isothermal magnetization data indicate a mixed magnetic state with ~2/3 of the material remaining FM and ~1/3 becoming antiferromagnetic (AFM) after cooling in a zero magnetic field. The AFM state fully transforms into the FM state via a field-induced metamagnetic transition, and the critical field is ~HC = 34 kOe at 2 K. Another kind of metamagnetic transition is observed above the low-field TC, where a field-induced metamagnetic transition is between the paramagnetic (PM) and FM states. Both metamagnetic transitions are accompanied by large thermal and magnetic hystereses, and the Arrott plots confirm that the transitions are first order in nature. A large magnetocaloric effect in the La0.9Nd0.1Fe12B6 compound is observed in the vicinity of the field-induced PM-FM transition.

Magnetization measurements reveal the onset of magnetic ordering at T C = 65 K followed by three additional magnetic anomalies at T 1 = 47 K, T 2 = 28 K, and T 3 = 11 K in Gd 117 Co 56.4 Sn 114.3 – a compound with a giant cubic unit cell that crystallizes in the Dy 117 Co 56 Sn 112 structure type with space group F m 3 ¯ m and lattice parameter a = 30.186 A. The magnetic ordering temperature increases with applied magnetic field; however, the analysis of magnetic data indicates that antiferromagnetic interactions also play a role in the ground state. AC magnetic susceptibility confirms multiple magnetic anomalies and shows minor frequency dependence. The local magnetic ordering below 60 K is supported by the Mossbauer spectroscopy. A single broad anomaly is detected at T 3 in the heat capacity; we suggest that magnetic domains form below this temperature. These data highlight unique features of magnetism in this and, potentially, other rare-earth intermetallics crystallizing with giant unit-cells where the exchange correlation lengths are much shorter when compared to the periodicity of the crystal lattice.

Materials responding vigorously to minor variations of external stimuli with negligible hysteresis could revolutionize many of the energy technologies, including refrigeration, actuation, and sensing. We report a combined experimental and theoretical study of a two-phase composite, naturally formed at the LaFe2Si stoichiometry, which exhibits a nearly anhysteretic, two-step first-order ferromagnetic-to-paramagnetic phase transformation with enhanced sensitivity to an external magnetic field. Other unusual properties include a large plateau-like positive magnetoresistance, magnetic-field-induced temperature and entropy changes occurring over a wide temperature range, and a Griffiths-like phase associated with short-range ferromagnetic clustering in the paramagnetic state. The heat capacity, magnetization, Mossbauer spectroscopy, and electrical resistivity, all exhibit characteristic, unusually sharp, first-order discontinuities even in magnetic fields as high as 100 kOe. We expect that similar phenomena could be designed in other mixed-phase systems, leading to novel functionalities, such as giant caloric effects in many yet undiscovered or/and underperforming intermetallic compounds.

Proper coupling between structural and magnetic transitions is critical for the emergence and control of magnetocaloric effects in solids. We examine the influence of minor substitutional doping (replacing Mn by Cr and Al by Sn) and interstitial doping with B on the magnetic, structural, and magnetocaloric properties of recently discovered Mn0.5Fe0.5NiSi0.94Al0.06 alloy exhibiting a giant magnetocaloric effect near room temperature. We demonstrate that magnetocaloric properties of the base compound can be controlled and, in some cases, improved by chemical substitutions. First-principles computations elucidate how small changes in the composition affect properties in this family of compounds and, thus, provide useful guidance for the selection of suitable doping elements for such materials. The magnetic-field-induced entropy change measured for Mn0.5Fe0.5NiSi0.94Al0.06B0.005 is −22 J/kg K near room temperature for the applied magnetic field of 2 T, and it is among the highest known values for this class of materials.

Two borophosphates, (NH4)1–2xM1+x(H2O)2(BP2O8)·yH2O with M = Mn (I) and Co (II), synthesized hydrothermally crystallize in enantiomorphous space groups P6522 and P6122 with a = 9.6559(3) and 9.501(3) A, c = 15.7939(6) and 15.582(4) A, and V = 1275.3(1) and 1218.2(8) A3 for I and II, respectively. Both compounds feature helical chains composed of vertex-sharing tetrahedral PO4 and BO4 groups that are connected through O atoms to transition-metal cations, Mn2+ and Co2+, respectively. For the two crystallographically distinct transition-metal cation sites present in the structure, this results in octahedral coordination with different degrees of distortion from the ideal symmetry. The crystal-field parameters, calculated from the corresponding absorption spectra, indicate that Mn2+ and Co2+ ions are located in a weak octahedral-like crystal field and suggest that the Co–ligand interactions are more covalent than the Mn–ligand ones. Luminescence measurements at room temperature reveal an orange emission that ...

Replacement of strongly magnetic gadolinium with weakly magnetic scandium unexpectedly enhances ferromagnetic interactions in (Gd1–xScx)5Ge4. Based upon this counterintuitive experimental finding we demonstrate the unique role 3d1 electrons of scandium atoms play in mediating magnetic interactions between the gadolinium atoms from the neighboring layers in the Sm5Ge4-type crystal lattice. Scandium substitutions at and below 20% rapidly increase the Curie temperature, TC, of the Gd5Ge4 parent, eliminate both the kinetic arrest and hysteresis, and drastically improve reversibility of the first-order magnetostructural transformation at TC. In agreement with first-principles predictions, higher than 20% Sc leads to the formation of a closely related Pu5Rh4-type structure where the first-order magnetostructural transformation is replaced by a conventional second-order ferromagnetic ordering that remains accompanied by a continuous rearrangement of the crystal lattice. Comparison of two materials with similar s...

The most favorable structures and the types of magnetic ordering predicted from first-principles-based methods in a family of closely related transition-metal-rich indides EuT5In (T = Cu, Ag, Au) are gauged against relevant experiments. The EuT5In compounds adopt a different structure for each different coinage metal—EuCu5In (hR42; R3m, a = 5.0933(7), c = 30.557(6) A), EuAg5In (oP28; Pnma, a = 9.121(2), b = 5.645(1), c = 11.437(3) A), and EuAu5In (tI14; I4/mmm, a = 7.1740(3), c = 5.4425(3) A)—and crystallize with the Sr5Al9, CeCu6, and YbMo2Al4 structure types, respectively. EuCu5In and EuAg5In order antiferromagnetically at TN = 12 and 6 K, respectively, whereas EuAu5In is ferromagnetic below TC = 13 K. EuCu5In exhibits complex magnetism: after the initial drop at TN, the magnetization rises again below 8 K, and a weak metamagnetic-like transition occurs at 2 K in μ0H = 1.8 T. The electronic heat capacity of EuCu5In, γ = ∼400 mJ/(mol K2), points to strong electronic correlations. Spin-polarized densitie...

A family of bis(trifluoromethanesulfonyl)amide-based ionic liquids of composition [RE5(C2H5-C3H3N2-CH2COO)16(H2O)8](Tf2N)15 (RE = Er, Ho, Tm; C3H3N2 ≡ imidazolium moiety) featuring the cationic, record quindecim {15+} charged pentanuclear rare earth (RE)-containing ion [RE5(C2H5-C3H3N2-CH2COO)16(H2O)8]15+ has been synthesized and characterized. In addition, due to the presence of rare earth ions, these ionic liquids show a response to magnetic fields with the highest effective magnetic moment observed so far for an ionic liquid and are rare examples of ionic liquids showing luminescence in the near-infrared. These ionic liquids also were successfully employed in a three-component synthesis of 2-pyrrolo-3′-yloxindole with an extremely low (

The magnetocaloric effect of gadolinium has been measured directly in pulsed magnetic fields up to $62\phantom{\rule{0.16em}{0ex}}\mathrm{T}$. The maximum observed adiabatic temperature change is $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}=60.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the initial temperature ${T}_{0}$ being just above $300\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The field dependence of $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$ is found to follow the usual ${H}^{2/3}$ law, with a small correction in ${H}^{4/3}$. However, as $H$ is increased, a radical change is observed in the dependence of $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$ on ${T}_{0}$, at $H=\mathrm{const}$. The familiar caret-shaped peak situated at ${T}_{0}={T}_{\mathrm{C}}$ becomes distinctly asymmetric, its high-temperature slope becoming more gentle and evolving into a broad plateau. For yet higher magnetic fields, ${\ensuremath{\mu}}_{0}H\ensuremath{\gtrsim}140\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, calculations predict a complete disappearance of the maximum near ${T}_{\mathrm{C}}$ and an emergence of a new very broad maximum far above ${T}_{\mathrm{C}}$.

We describe magnetic, thermal, and magnetocaloric properties of rare earth intermetallic compounds Tm x Dy 1 − x Al 2 with x = 0.25, 0.5 and 0.75. Using model Hamiltonian we consider contributions of the crystalline electric field anisotropy in both Tm and Dy magnetic sublattices, disorder in exchange interactions among Tm-Tm, Dy-Dy and Tm-Dy magnetic ions, and the Zeeman effect. Employing earlier reported and new experimental measurements, we first determine a single free variable – the intersublattice magnetic exchange parameter – to properly model the temperature and magnetic field dependencies of heat capacity and magnetization, and then use the modeling results to explain the emergence of an anomalous spin reorientation transition and its influence on the magnetocaloric effect in the title compounds. Theoretical results agree with experimental data reasonably well.

The structure and magnetic properties of Nd(Al1-xFex)2 alloys with x = 0, 0.05, 0.1 and 0.2, which adopt cubic MgCu2-type structure with space group Fd 3 ¯ m, are studied using x-ray powder diffraction, static and dynamic magnetization, and calorimetric measurements. The lattice constant decreases linearly with increasing Fe content from 8.0106(4) A to 7.9044(4) A. Large thermal irreversibilities between zero-field-cooled and field-cooled conditions are observed for all substituted samples. The magnetic transition temperatures exhibit a minimum for x = 0.1, and coercive fields at 2 K increase from 70 Oe for x = 0 to 6.3 kOe for x = 0.2. The absence of λ-type peak in the heat capacity data, frequency dependence of ac magnetic susceptibility, and memory effects indicate formation of a cluster-glass magnetic state when x ≥ 0.1.

Increasing demand for lithium-ion batteries (LIBs) that serve as power source for diverse electronic devices, electrical propulsion systems and other applications, calls for economical and environmentally benign recycling of spent LIBs and recovery of critical elements such as Co and Li from rapidly growing volumes of battery wastes. The presented study explores mechanochemical extraction of Co and Li from lithium cobaltate (LiCoO2), which serves as cathode material in commercial LIBs. Our investigation reveals that solvent-free mechanochemical processing can successfully convert pure, reagent grade LiCoO2 into metallic Co and Li-derivatives that are suitable for the further recovery of Li. We also show that the proposed approach can be successfully applied to reclaiming these critical elements from commercial LIBs. Due to its magnetic nature, metallic Co is easy to separate from non-magnetic components of mechanochemically generated powder mixtures using an appropriate magnetic separation technique, while Li can be reclaimed as Li2CO3 after an additional liquid-phase processing. The recovery rates achieved during our experiments with pure LiCoO2 are ∼90% for Co and ∼70% for Li.

Rare-earth anti-perovskites with oxygen are an interesting magnetic materials family at the boundary between intermetallics and oxides, they however remain largely unexplored. Here, magnetic and heat capacity investigations, as well as density functional theory (DFT) calculations, were carried out on SnOEu3. At low magnetic field (B ≤ 0.5 T), a Neel temperature separates antiferromagnetic and paramagnetic phases at 31 K. When applying higher magnetic field below the Neel temperature, successive transformations toward a ferromagnetic state via a number of intermediate canted magnetic structures are observed and are associated with only modest latent heat and transition entropy. High-pressure magnetic measurements confirm the stable divalent state of Eu up to 1.05 GPa. A direct magnetocaloric effect progressively increases with applied magnetic field above the Neel temperature, reaching −16 J kg–1 K−1 for ΔB = 7 T. On the other hand, the inverse magnetocaloric effect of the field-induced transition below TN saturates at ~+5 J kg−1 K−1. DFT calculations support magnetic instabilities observed experimentally in SnOEu3 and reveal an unusual exchange mechanism and band topology near the Fermi level.

We have investigated the effects of quenching rate on the thermal dependence of the magnetic entropy change ΔSM(T) and the magnetic field induced hysteresis loss through the antiferromagnetic (AFM) ↔ ferromagnetic (FM) transformation in bulk Fe49Rh51. Two nearly identical square-prism-shaped samples were subjected to two different temperature cooling regimes; one was rapidly quenched (FQ) in iced-water and another slow cooled (SC) to room temperature at a cooling rate of 2 K/min. The temperature of the AFM ↔ FM transition is similar for both samples, but the FQ sample shows much sharper temperature- and magnetic field-induced magnetization change; in addition, the total magnetization change is 14% larger. In FQ material, the magnetocaloric effect, i.e., ΔSM(T) quickly approaches saturation above 1 T and shows a large peak value at 2 T (13.9 versus 8.9 Jkg−1 K−1 in SC material), but a larger average hysteresis loss FWHM in the temperature range coinciding with of the full-width at half-maximum of the ΔSM(T) curve.

Crystallographic, magnetic, electrical transport and thermodynamic properties of pseudo-binary Nd7Ni2Pd compound have been studied using temperature-dependent x-ray powder diffraction and physical property measurements. Compared to the ferromagnetic parent Nd7Pd3, the ground state of Nd7Ni2Pd is antiferromagnetic, and it exhibits strong metamagnetism. The measurements indicate two antiferromagnetic transitions in fields less than 8 kOe: a second-order paramagnetic to antiferromagnetic at TN2 = 29 K and a weak first-order antiferromagnetic to antiferromagnetic transition at TN1 = 24.5 K. The compound becomes ferromagnetic in fields of 8 kOe and higher with TC = 30 K. Temperature dependence of lattice parameters is anomalous, most prominently in the basal plane at ∼30 K; however, there is no detectable structural distortion or clear volume discontinuity around 25 K, suggesting a significant weakening of the first-order transition when compared to the binary Nd7Pd3.