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We examine structural and magnetic properties of a series of La–Fe–Si alloys in the region of concentrations where they naturally form two-phase LaFeSi–LaFe13−xSix composites with variable content and connectivity of LaFe13−xSix grains distributed within the LaFeSi matrix. Theoretical calculations confirm that the LaFeSi constituent is magnetically and structurally inert below room temperature and at pressures between −10 and 10 GPa. The LaFe13−xSix constituent, on the other hand, is magnetically and structurally active: it exhibits first-order magnetostructural transformations that, in addition to xSi, can be controlled with temperature, magnetic field, and pressure. In composites where the concentration of the inactive constituent is ∼70 wt. % or greater, the standard, single-step, LaFe13−xSix first-order phase transformation proceeds in two steps separated by over 30 K in a zero magnetic field. Increasing the magnetic field recouples the two steps and restores the single-step phase transformation pathway. We analyze the roles of stresses caused by both thermal expansion mismatch and the first-order magnetic phase transition in LaFe13−xSix to rationalize the observed physical behaviors that emerge as the temperature or/and magnetic field vary. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The influence of magnetic field cycling through the first-order magnetostructural transformation on the magnetic and magnetocaloric properties, as well as hysteresis of polycrystalline Gd5Si2Ge2, has been studied using magnetometry. The cycling has a minimal effect on the magnetic field-induced entropy change and the phase transformation temperature of the material. On the other hand, magnetic hysteresis decreases by 30% after approximately ten cycles and remains low unless the sample is moved far into the paramagnetic regime. Factors playing a role in the history dependence of hysteresis have been discussed. [ABSTRACT FROM AUTHOR]

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., Mn 0.5 Fe 0.5 NiSi 1-x Al x [ 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 Ni 2 In-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. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Co2MnSb thin films were grown on glass and GaAs (001) substrates using pulsed laser deposition. The films were grown in magnetic fields (HG = 500 Oe and 0 Oe) that were applied in the plane of the substrate during the deposition process. Angle-dependent magneto-optic Kerr effect measurements for films grown on glass revealed a uniaxial magnetic anisotropy in the direction of the applied growth field. Films grown on GaAs (001) exhibited more complicated magnetic anisotropy behavior, due to additional contributions from the substrate. Point contact Andreév reflection spectroscopy measurements indicated that the spin polarizations of the films were about P ∼ 50%, with negligible difference between films grown in zero and non-zero applied fields. [ABSTRACT FROM AUTHOR]

We report an unusual coexistence of ferromagnetism and ferrimagnetism, and metamagnetism in Pr0.6Er0.4Al2. In addition, this compound retains a clear Griffiths phase behavior even at 1 kOe magnetic field and shows a large exchange bias after field cooling from the paramagnetic state. The crystal-field excitations and opposite exchange interactions between nearest-neighbor and next-nearest-neighbor rare earth sites explain these behaviors. [ABSTRACT FROM AUTHOR]

Unique from other rare earth dialuminides, PrAl2 undergoes a cubic to tetragonal distortion below T = 30 K in a zero magnetic field, but the system recovers its cubic symmetry upon the application of an external magnetic field of 10 kOe via a lifting of the 4f crystal field splitting. The nuclear Schottky specific heat in PrAl2 is anomalously high compared to that of pure Pr metal. First principles calculations reveal that the 4f crystal field splitting in the tetragonally distorted phase of PrAl2 underpins the observed unusual low temperature phenomena. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic, magnetocaloric, and magnetotransport properties of RCo1.8Mn0.2 (R=Er, Ho, Dy, and Tb) were studied by room temperature X-ray diffraction, magnetization, and resistivity measurements at a temperature interval of 5–400K and magnetic fields up to 5T. The Curie temperature of RCo2 was found to increase significantly when 10% Mn was substituted for Co. The effective paramagnetic moments were found to be in reasonable agreement with their theoretical values. A large magnetoresistance (MR) of Δρ/ρ o ≈−13.5% for R=Ho at T≈153K for ΔH=5T has been observed. The maximum relative cooling capacities vary from 467J/kg at low temperature for R=Er to 202J/kg at the near room temperature for R=Tb. [Copyright &y& Elsevier]

Abstract: Magnetic shape memory properties of polycrystalline Ni50Mn35In15−x Si x were investigated. A reversible strain of more than 0.4% was observed for x =0 at a magnetic field H =5T that was found to be associated with a field induced reverse martensitic transformation. The strains were found to increase with the substitution of In by Si and strains larger than 1% were observed for x =2 at H =5T. Both the positive and negative strain changes were observed in the vicinity of martensitic transition temperatures. The strain in Ni50Mn35In15−x Si x was found to depend on silicon concentration, and on samples texture. [ABSTRACT FROM AUTHOR]

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 LaFe 2 Si 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, Mössbauer 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. [Display omitted] [ABSTRACT FROM AUTHOR]

The adiabatic temperature changes (ΔTad) in the vicinity of the Curie and martensitic transition temperatures of Ni50Mn35In15 and Ni50Mn35In14Z (Z=Al and Ge) Heusler alloys have been studied using an adiabatic magnetocalorimeter of 250-350 K temperature interval for applied magnetic field changes up to ΔH=1.8 T. The largest measured changes were ΔTad=-2 and 2 K near the martensitic (first-order) and ferromagnetic (second-order) transitions for ΔH=1.8 T, respectively. It was observed that |ΔTad|≈1 K for relatively small field changes (ΔH=1 T) for both types of transitions. The results indicate that these materials should be further explored as potential working materials in magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]

It is established, using magnetization measurements, that Ni50Mn36.5In13.5 is in a paramagnetic state (PS) above and below the martensitic transition temperature (TM). Magnetoresistance (MR) and magnetic entropy changes (ΔSM) in the vicinity of TM were studied. MR and ΔSM at TM were found to be ≈-8% and ≈+24 J Kg-1 K-1, respectively, at ΔH=5 T. Although MR and ΔSM values were lower than compared to those found in other Heusler systems, the significantly smaller hysteresis observed in Ni50Mn36.5In13.5 makes this compound, and other such compounds that undergo a martensitic transition in a PS, promising for the study and applications of magnetocaloric magnetic materials. [ABSTRACT FROM AUTHOR]

We have studied the effects of partial substitution of In by Si on the magnetic and exchange bias properties of bulk Ni50Mn35In15 Heusler alloys through magnetization measurements. Zero-field and field-cooled magnetization measurements were performed in fields up to 5 T. It was observed that an increase in the Si concentration strongly affects the ground state of the martensitic phase and the magnetic properties of compounds. It was found that exchange bias increases with increasing conduction electron concentration, and the maximum bias field was found to be ≈0.017 T at S K for a cooling field of H = 5 T. [ABSTRACT FROM AUTHOR]

Phase compositions and crystal structures of Gd6X2Si3 (X = Ni, Co,) and Ln6Co2Si3 (Ln = Pr, La) have been studied. The magnetic properties of Gd6X2Si3 (X = Ni, Co) and Ln6Co2Si3 (Ln = Pr, La) have been evaluated from magnetization measurements performed by a superconducting quantum interference device magnetometer in a temperature interval of 5-400 K, and at magnetic fields up to 5T. The crystal structures of Gd6X2Si3 (X = Co, Ni) and Ln6Co2Si3 (Ln = Pr, La) were found to be hexagonal at 300 K. The Curie temperature (TC), effective and magnetic moment of the compounds (at5 K) have been determined for Gd6X2Si3 (X = Ni, Co), and Ln6Co2Si3 (Ln = Pr, La). TC was found to depend on composition, and reaches maximum value of about 300 K for the Gd6X2Si3 system. Themagnetocaloric effect (magnetic entropy changes and relative cooling power (RCP) was found to depend on X and Ln, and the maximum RCP values were found to be larger than 500 J/kg near room temperature for the Gd6Ni2Si3 and Gd6Co2Si3 compounds. This value of RCP is comparable to the prototype magnetic refrigeration material, Gd. [ABSTRACT FROM AUTHOR]

Combined experimental and density functional theory (DFT) study of Pr 0.75 Gd 0.25 ScGe and its hydride (Pr 0.75 Gd 0.25 ScGeH) reveals intricacies of composition-structure-property relationships in those distinctly layered compounds. Hydrogenation of the intermetallic parent, crystalizing in a tetragonal CeScSi-type structure, leads to an anisotropic volume expansion, that is, a (= b) lattice parameter decreases while the lattice expands along the c direction, yielding a net increase of cell volume. DFT calculations predict an antiparallel coupling of localized Gd and Pr magnetic moments in both materials at the ground state. While experiments corroborate this for the parent compound, there is no conclusive experimental proof for the hydride, where Pr moments do not order down to 3 K. DFT results also reveal that rare-earth – hydrogen interactions reduce spin-polarization of the Pr and Gd 5 d and Sc 3 d states at the Fermi energy, disrupt indirect exchange interactions mediated by conduction electrons, dramatically reduce the magnetic ordering temperature, and open a pseudo-gap in the majority-spin channel. Both experiments and theory show evidence of Kondo-like behavior in the hydride in the absence of an applied magnetic field, whereas increasing the field promotes magnetic ordering and suppresses Kondo-like behavior. • Combined experimental and DFT investigation of structure-property relationships in Pr 0.75 Gd 0.25 ScGeH. • Hydrogen disrupts the magnetic exchange interactions allowing for competing Kondo interactions and magnetic fields. • DFT predicts antiparallel coupling of Pr and Gd at 0 K, however the Pr magnetic sublattice remains disordered down to 3 K. [ABSTRACT FROM AUTHOR]