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Graphical abstract Temperature dependence of the magnetic entropy change for α-Dy 2 S 3 single crystals in magnetic field change within 5 T H ‖ b (a) and H ⊥ b (b). Highlights • Specific heat measurements in the wide temperature/magnetic field range for α- R 2 S 3 (R = Tb, Dy) single crystals. • Effect of magnetic field on the specific heat near the successive AFM ordering temperatures. • Estimation of magnetic entropy change and adiabatic temperature change from specific heat in magnetic field. • Influence of magnitude and orientation of magnetic field on the magnetocaloric effect. Abstract The magnetocaloric effects (MCE) of α-Tb 2 S 3 and α-Dy 2 S 3 single crystals exhibiting successive antiferromagnetic (AFM) transitions have been investigated by analyzing specific heat measured in magnetic field. The temperature dependence of specific heat in the vicinity of the successive transitions shows obvious distinction depending on the orientations of the applied magnetic field for both α-Tb 2 S 3 and α-Dy 2 S 3 that having orthorhombic crystal structures. When the magnetic field is increased, the specific heat is as follows: For α-Tb 2 S 3 in H ‖ b , the peak around T N2 shifts to lower temperature but the other one peak around T N1 barely moves; In H ⊥ b , the peak around T N2 has no shift almost within 3 T but suddenly moves to lower temperature in 4 T and the other one peak around T N1 shifts to lower temperature in specific heat versus temperature. In the case of α-Dy 2 S 3 , the two peaks around T N2 and T N1 shift to lower temperatures in H ‖ b but move to higher temperatures when the magnetic field is increased up to 5 T by H ⊥ b in spite of antiferromagnetic transitions. Therefore, the maximum value and corresponding temperature of both isothermal magnetic entropy change (Δ S m) and adiabatic temperature change (Δ T ad) in the magnetic field H ⊥ b are extremely different in low temperature range from that in the field of H ‖ b . The results propone that the MCE of α-Tb 2 S 3 and α-Dy 2 S 3 could be controlled at low temperature by the magnitude and orientation of magnetic field. It also indicates that the refrigerating capacity and thermal absorption capacity will be controlled by changing magnitude and orientation of magnetic field on the α-Tb 2 S 3 and α-Dy 2 S 3 single crystals. [ABSTRACT FROM AUTHOR]

The effects of Si substitution for As on the magnetic and magnetocaloric properties of MnFeP0.5As0.5-xSix compounds have been investigated. The Si-substituted compounds MnFeP0.5As0.5-xSix with x=0, 0.1, 0.2, and 0.3 have been prepared by high-energy ball milling and solid-state reaction. X-ray diffraction shows that all the MnFeP0.5As0.5-xSix compounds crystallize in the Fe2P-type structure. Magnetic measurements show that the compounds are ferromagnetic with a nonlinear dependence of TC on Si content. All compounds exhibit a field-induced first-order magnetic phase transition. The magnetic-entropy change is derived from the magnetization data by using the Maxwell relations. The maximum magnetic-entropy change observed in this system reaches about 32 J/kg K for a field change from 0 to 2 T for x=0.2, at temperature around 294 K. [ABSTRACT FROM AUTHOR]

We have studied the first-order magnetic phase transition and related physical properties of MnFeP[SUB0.5]As[SUB0.4]Si[SUB0.1] by means of x-ray diffraction, magnetization, thermal expansion, and electrical resistance measurements. The compound crystallizes in the hexagonal structure with Fe[SUB2]P-type. The temperature dependence of magnetization shows a first-order magnetic phase transition around 299 K. There is no crystallographic structural transition associated with the magnetic phase transition. The linear thermal expansion shows that this magnetic phase transition is accompanied by a negative volume change. The electrical resistance shows an anomalous behavior at the transition, which is probably caused by the change in c/a ratio. [ABSTRACT FROM AUTHOR]

We have studied the magnetocaloric effect (MCE) in GdRu[sub 2]Ge[sub 2] by means of measurements of temperature and field dependence of the specific heat and the magnetization. Two anomalies were observed at T[sub 1=29K and T[sub 2]=32K in the zero-field specific-heat curve. Magnetization measurements showed that the magnetic moments of the Gd ions order antiferromagnetically below T[sub 2] and follow the Curie-Weiss Law above T[sub 2]. The magnetic measurements also showed that there exists a field-induced antiferromagnetic to ferromagnetic transition below T[sub 1]. The magnetocaloric properties estimated from the magnetization measurements by means of the thermodynamic Maxwell relation are in good agreement with those obtained from the specific-heat measurements. The largest observed adiabatic temperature change, Δ T[sub ad], is approximately 10 K for a field change from 0 to 15 T. The considerably large magnetic entropy change is due to the field-induced magnetic phase transition, which is magnetically reversible. [ABSTRACT FROM AUTHOR]

We have studied the magnetic properties and magneto-caloric effect in the compound Tb[sub 5]Ge[sub 2]Si[sub 2] by means of magnetic measurements. The compound Tb[sub 5]Ge[sub 2]Si[sub 2] is a canted antiferromagnet with Gd[sub 5]Ge[sub 2]Si[sub 2]-type monoclinic structure. The ordering temperature is about 76 K. Above the ordering temperature, a field-induced first-order phase transition was observed in the magnetization curves with increasing and decreasing fields. The magnetic entropy changes have been calculated from the magnetization data based on the thermodynamic Maxwell relation. The character of the magnetic entropy changes, depending on the field and temperature, is similar to that in the Gd[sub 5]Ge[sub 2]Si[sub 2] compound. There is hardly any influence of the magnetic anisotropy on the magneto-caloric effects in Tb[sub 5]Ge[sub 2]Si[sub 2]. [ABSTRACT FROM AUTHOR]

Abstract: The high quality La x Ce1− x B6 (x =0, 0.2, 0.4, 0.6, 1) single crystals with large emission current density have been successfully grown by floating zone method. The crystal structure, crystal quality and emission properties of La x Ce1−xB6 single crystals were characterized by 360° Phi scanning single crystal diffractometer, X-ray Laue diffraction and the thermal electron emission measurements. It is found that the as-grown crystals have a good crystal quality without subgrains and twin crystal phenomenon. The thermionic emission measurement results show that the maximum emission current density on (100) surface of La0.2Ce0.8B6 single crystal is 71.2A/cm2 at 1873K under an applied voltage of 800V, which is larger than the reported values in the literatures up to now. Furthermore, the crystals with different components also show a higher emission current density such as 53.8A/cm2 for La0.4Ce0.6B6 and 53.3A/cm2 for CeB6 single crystals. The field emission single tip made by LaB6 single crystal shows a superior performance than the polycrystalline LaB6 field emission tip and its field enhancement factor (β) is 36,231cm−1. Thus, the La x Ce1− x B6 single crystals will have promising application prospects as a hot or cold cathode. [Copyright &y& Elsevier]

The structural and magnetocaloric properties of Mn1.35Fe0.65P1-xSix compounds are investigated. The Sisubstituted compounds, Mn1.35Fe0.65P1-xSix with x = 0.52, 0.54, 0.55, 0.56, and 0.57, are prepared by high-energy ball milling and the solid-state reaction. The X-ray diffraction shows that the compounds crystallize into the Fe2P-type hexagonal structure with space group P62m. The magnetic measurements show that the Curie temperature of the compound increases from 253 K for x = 0.52 to 296 K for x = 0.56. The isothermal magnetic-entropy change of the Mn1.35Fe0.65P1-xSix compound decreases with the Si content increasing. The maximal value of the magnetic-entropy change is about 7.0 J/kg·K in the Mn1.35Fe0.65P0.48Si0.52 compound with a field change of 1.5 T. The compound quenched in water possesses a larger magnetic entropy change and a smaller thermal hysteresis than the non-quenched samples. The thermal hysteresis of the compound is less than 3.5 K. The maximum adiabatic temperature change is about 1.4 K in the Mn1.35Fe0.65P0.45Si0.55 compound with a field change of 1.48 T. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic refrigeration employing magnetically ordered materials is a relatively novel technique, differing in some respects from magnetic cooling by means of adiabatic demagnetization of paramagnetic substances. Magnetic refrigeration has been known for more than a century and is based on the magnetocaloric effect. It has received new impetus recently because it has several advantages over vapor-compression refrigeration. In the last few years the magnetic and magnetocaloric properties of a large number of intermetallic compounds were investigated, in which the magnetic moments are carried by atoms of 3d transition elements. In the present paper we will focus on intermetallic compounds in which one of the components is Mn. The results obtained on several groups of such intermetallic compounds will be reviewed. By far the most promising materials of this group of intermetallics are compounds of the type MnFeP1−x As x . Although it is understood that these compounds are probably nontoxic, the presence of As atoms in them might form a mental barrier to exploit these materials on a commercial basis. Special attention will therefore be paid to efforts attempting to substitute other elements for As in MnFeP1−x As x with the proviso that the favorable magnetocaloric properties be retained. [Copyright &y& Elsevier]

Abstract: The structure and magnetic properties of Gd2Co17−x Cr x (1.17≤ x ≤3.0) compounds have been investigated by means of X-ray diffraction (XRD) and magnetization measurements. The powder X-ray diffraction patterns show that all samples crystallize as a single phase with the rhombohedral Th2Zn17-type structure. The lattice parameters a and the unit cell volume V increases slightly with increasing Cr content, but the c parameter varies in a less simple way with increasing Cr content. The X-ray diffraction patterns of the magnetically aligned samples show that all compounds investigated have uniaxial anisotropy. Spin reorientation phenomena occur in all of the compounds. The Curie temperature T C, the spin reorientation temperature T sr, the spontaneous magnetization M 0 and the saturation magnetization M s decrease with the increasing Cr content. The anisotropy constant K 1 and the anisotropy field B a of the compounds at room temperature reach a maximum for x =1.76. The M 0 and M s increase with increasing temperature from 5K to 300K. The easy-axis anisotropy of all compounds changes to easy-plane anisotropy at low temperatures and the spin reorientation phenomena are more pronounced for low Cr concentration. [Copyright &y& Elsevier]

Abstract: Modern society relies on readily available refrigeration. The ideal cooling machine would be a compact, solid state, silent and energy-efficient heat pump that does not require maintenance. Magnetic refrigeration has three prominent advantages compared to compressor-based refrigeration. First, there are no harmful gases involved, second it may be built more compact as the working material is a solid and third magnetic refrigerators generate much less noise. Recently, a new class of magnetic refrigerant materials for room-temperature applications was discovered. These new materials have important advantages over existing magnetic coolants: They exhibit a large magnetocaloric effect (MCE) in conjunction with a magnetic phase transition of first order. This MCE is, larger than that of Gd metal, which is used in the demonstration refrigerators built to explore the potential of this evolving technology. In the present review, we compare the different materials considering both scientific aspects and industrial applicability. [Copyright &y& Elsevier]

Abstract: Spin reorientation transitions and magnetic anisotropy in Y2Co17−x Cr x (x =1.17–3.0) compounds have been investigated by means of X-ray diffraction and magnetization measurements. The powder X-ray diffraction patterns show that most samples crystallize as a single phase with the rhombohedral Th2Zn17-type structure. However, in the compound Y2Co14Cr3 the Th2Zn17 phase coexist with the hexagonal Th2Ni17-type phase. The lattice parameters a and c hardly change and the unit cell volume V increases slightly with increasing Cr content. The X-ray diffraction patterns of the aligned powder of the samples have confirmed that at room temperature the compound with x =1.17 has planar anisotropy, but the compounds with x =1.76, 2.34 and 3.00 have uniaxial anisotropy. Spin reorientation phenomena occur in all of the compounds. With increasing Cr content, the Curie temperature, the spin reorientation temperature, the spontaneous magnetization, and the anisotropy constant K 2 of the Y2Co17−x Cr x (x =1.17–3.0) compounds decrease strongly while the anisotropy constant K 1 increases in the range of x from 1.17 to 2.34 and then decreases in the range of x from 2.34 to 3.00. [Copyright &y& Elsevier]

Abstract: We have studied the magnetic properties and magnetic-entropy changes of Mn1.1Fe0.9P0.7As0.3–x Ge x compounds with x =0, 0.05, 0.1, 0.15 and 0.3. X-ray diffraction (XRD) study shows all the compounds crystallize in the Fe2P-type structure. Magnetic measurements show that the Curie temperature increases from 150K for Mn1.1Fe0.9P0.7As0.3 to 380K for Mn1.1Fe0.9P0.7Ge0.3. A field-induced first-order magnetic phase transition is observed above the Curie temperature for the compounds with x up to 0.15. There exists an optimal composition in which the first-order phase transition is the sharpest. The optimal composition for this system is x =0.1. The maximal magnetic-entropy change derived from the magnetization data is about 40J/(kg K) for a field change from 0 to 3T. [Copyright &y& Elsevier]

The alloy MnFeP0.45As0.55 has been identified as a promising material to be used as magnetic refrigerant for room-temperature applications. This alloy, which is derived from the well-known iron pnictide Fe2P, exhibits a first-order temperature- and field-induced magnetic phase-transition. The Curie temperature can be varied by substitutions into the pnictide sublattice. We studied the effect of Ge substitution in this material. Most strikingly, we find a strong increase of the magnetic ordering temperature up to 570 K and a concomitant increase of the ordered magnetic moment up to 4.25 μB/f.u. for the alloy MnFeP0.5Ge0.5. On substitution with the large Ge ions, the expected lattice expansion is very anisotropic. We observe an increase and decrease of the a and c parameter of the hexagonal lattice, respectively. Compared with the (P,As) series, for a similar volume change we find a much stronger increase of TC. This confirms the importance of competing exchange interactions in this interesting alloy system. [Copyright &y& Elsevier]

A new magnetic-refrigeration-cycle model using ferromagnetic materials as a cyclic working substance is set up, in which finite-rate heat transfer, heat leak and regeneration time are taken into account. On the basis of the thermodynamic properties of a ferromagnetic material, the general performance characteristics of the ferromagnetic Stirling refrigeration cycle are investigated and the effects of some key irreversibilities on the performance of the cycle are revealed. By using the optimal-control theory, the optimal relation between the coefficient of performance and the cooling rate is derived and some important performance bounds, e.g., the maximum cooling rate, the maximum coefficient of performance, are determined. Moreover, the optimal operating regions for cooling rate, coefficient of performance and the optimal operating temperatures of a cyclic working substance in the two heat-transfer processes are obtained. Furthermore, the influences of magnetization and magnetic field on the performance characteristics of the cycle are discussed. The results obtained here have general significance and can be deduced to the related ones of the Stirling refrigeration cycle using paramagnetic salt as a cyclic working substance. [Copyright &y& Elsevier]

Modern society relies very much on readily available cooling. Magnetic refrigeration based on the magneto-caloric effect (MCE) has become a promising competitive technology for the conventional gas-compression/expansion technique in use today. Recently, there have been two breakthroughs in magnetic-refrigeration research: one is that American scientists demonstrated the world''s first room-temperature, permanent-magnet, magnetic refrigerator; the other one is that we discovered a new class of magnetic refrigerant materials for room-temperature applications. The new materials are manganese–iron–phosphorus–arsenic (MnFe(P,As)) compounds. This new material has important advantages over existing magnetic coolants: it exhibits a huge MCE, which is larger than that of Gd metal; and its operating temperature can be tuned from about 150 to about 335 K by adjusting the P/As ratio. Here we report on further improvement of the materials by increasing the Mn content. The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field. Addition of Mn reduces the thermal hysteresis, which is intrinsic to the first-order transition. This implies that already moderate applied magnetic fields of below 2 T may suffice. [Copyright &y& Elsevier]

We have studied the magnetocaloric properties of a variety of compounds, like Gd5(Si1−xGex)4 with x=0.576 and 0.5875, MnFeP1−xAsx with x between 0.25 and 0.65, RTiGe with R=Tb, Dy, Ho, Er and Tm, Ni53Mn22Ga25, Mn5Si3, and Mn1.95Cr0.05Sb. These compounds have in common that they exhibit either temperature- or field-induced first-order magnetic-phase transitions. Gd5(Si1−xGex)4 exhibits simultaneously a magnetic and a structural transition, which is accompanied by a huge magnetic-entropy change. A temperature-induced ferromagnetic (FM) to paramagnetic (PM) transition and a magnetic-field-induced PM to FM transition which are both of first order are observed in MnFeP1−xAsx compounds. Here the magnetic-phase transitions are not accompanied by structural transitions. Nevertheless, a large magnetic-entropy change, comparable with that in Gd5(Si1−xGex)4, is observed in the MnFeP1−xAsx compounds. In several of the RTiGe compounds, an applied magnetic field induces an antiferromagnetic (AF) to FM phase transition. Here, we observed a magnetic anisotropy dependence of the magnetic-entropy change. The Heusler alloy Ni53Mn22Ga25 exhibits a first-order martensitic transformation accompanied by a magnetic-phase transition around 220 K. The magnitude and the shape of the magnetic-entropy changes observed for this compound are quite different. Mn5Si3 compound exhibits two successive first-order magnetic-phase transitions and shows a different type of magnetocaloric effect (MCE). Mn1.95Cr0.05Sb exhibits an AF to FM phase transition and a negative MCE. The relationship between the magnetic-phase transitions and the MCE is discussed, based on the comparison of the observed MCEs and the exchange interactions in these materials. [Copyright &y& Elsevier]

We have studied the crystal structure, magnetic structure and magnetic properties of the tetragonal compounds HoTiGe and ErTiGe by means of neutron diffraction and magnetic measurements. The neutron-diffraction measurements were made in the range from 1.7 K to temperatures above the corresponding magnetic-ordering temperatures (TN=88 and 41 K, respectively). Both compounds have a simple antiferromagnetic structure with a propagation vector q=(0, 0, 0.5). The Ho moments have a preferred moment direction along the tetragonal c-axis at all temperatures in the magnetically ordered regime, while the direction is perpendicular to the c-axis for the Er moments. This difference in easy moment direction has been discussed in terms of a crystal-field-induced rare-earth-sublattice anisotropy. The magnetic measurements showed that both compounds give rise to metamagnetic transitions in their magnetically ordered states. This field-induced transition is particularly pronounced in HoTiGe where it is accompanied by a strong hysteresis in the lower-temperature range. [Copyright &y& Elsevier]

Abstract: The structural and magnetic properties of MnCo1−x V x Ge (x =0.00, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20 and 0.30) compounds were investigated by means of X-ray diffraction, scanning electron microscopy and magnetization measurements. The MnCo1−x V x Ge compounds crystallize in the orthorhombic TiNiSi-type crystal structure for x ≤0.02 and in the hexagonal Ni2In-type structure for x >0.02. The magnetization measurements show that the MnCo1−x V x Ge compounds exhibit a complex magnetic behavior. The Curie temperature can be tuned from 360K to 148K by increasing x. The maximal magnetic-entropy change is 3.9J/kgK for x =0.06 at a field change from 0 to 1.5T at about 265K. [Copyright &y& Elsevier]

Abstract: We have performed powder X-ray-diffraction measurements on in fields up to 5T in the temperature range 8–310K. The compound which has the hexagonal type of structure shows a field-induced isostructural phase transition. We found that the cell volume decreases slightly and continuously with increasing magnetic field, although the lattice parameter ratio c/a drastically changes. A tentative analysis of the dependence of the lattice parameters on the magnetization has been carried out using the extended Bean–Rodbell model. [Copyright &y& Elsevier]

• Structural and magnetic phase diagrams of MnFe 0.6 Ni 0.4 Si 1− x Ge x alloys (0 ≤ x ≤ 1) are reported. • Magneto-structural transition is found at 204 K for x = 0.5. • DSC experiments reveal a recalescence event at the first cooling. • In-field specific heat measurements are used to obtain the magnetocaloric effect. • A sizable magnetocaloric temperature change is found for x = 0.5. The structural and magnetic phase diagrams of MnFe 0.6 Ni 0.4 Si 1− x Ge x alloys (0 ≤ x ≤ 1) are explored using powder X-ray diffraction, magnetic and calorimetric measurements. At room temperature, the crystal structure evolves from the orthorhombic TiNiSi-type to the hexagonal Ni 2 In-type with the increase in Ge. A magneto-structural coupling leading to a first-order ferromagnetic transition is found at 204 K for x ~ 0.5. Differential scanning calorimetry reveals a recalescence-like event at the first cooling across the structural transition. In-field specific heat measurements are used to quantify the giant magnetocaloric effect and show that the latent heat of the magneto-structural transition is less than in closely related Mn MX alloys, which leads to sizable transition sensitivity to the magnetic field and finite adiabatic temperature change. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of MnFe1-xCox Ge compounds with x = 0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.85,0.9, and 1.0 were investigated by means of X-ray diffraction (XRD) and magnetization measurements. XRD shows that the MnFe1-x Cox Ge compounds crystallize in the hexagonal Ni2In-type crystal structure for x ≤ 0.8 and in the orthorhombic NiTiSi-type structure for x > 0.8. The magnetization measurements show that the MnFe1-x Cox Ge compounds exhibit a complex magnetic behavior. The Curie temperature increases with increasing of x. The saturation magnetization of the compounds with Ni2In type structure increase with increasing of x and the saturation of the magnetization in the NiTiSi-type structure also increases with increasing x. We investigated the magnetocaloric effects in these compounds by means of magnetization measurements. The maximum magnetic-entropy change observed in these compounds reaches 9 J/kgK for x = 0.8 in a field change from 0 to 5 T at around 289 K. [ABSTRACT FROM AUTHOR]

Novel three-dimensional YVO 4 :Ln3+ (Ln3+ = Eu3+, Sm3+, Dy3+, Tm3+) hierarchitectures were successfully fabricated on glass substrate by a simple, hydrothermal process by using disodium ethylenediaminetetraacetic acid (Na 2 H 2 L, where L4− = (CH 2 COO) 2 N(CH 2) 2 N(CH 2 COO) 2 4−)) as a capping agent. The shape and size of product can be tailored by controlling the reaction time and the Na 2 H 2 L/Y3+ molar ratio. As a typical morphology, YVO 4 :Eu3+ shows a flower-like hiearchitecture, which is composed of a primary microrod trunk and a large number of secondary nanonails. The trunk is a rectangle prism with a length of 2 μm. The nanonail branch has a length of 400 nm and a diameter of 80 nm, and its cap has a diameter of 100 nm with a thickness of 20 nm. A possible formation mechanism of this flower-like hierarchical structure was proposed, and it is investigated in detail through time evolution experiments. Under UV radiation, the thin film samples were shown the emission characteristic of Eu3+ (5D 0 →7F 2 , 618 nm), Dy3+ (4F 9/2 → 6H 13/2 , 575 nm), Sm3+ (4G 5/2 → 6H 7/2 , 603 nm), Tm3+ (1G 4 →3H 6 , 478 nm), and morphology-sensitive photoluminescent properties. Image 1 • Flower-like YVO 4 :Ln3+ hierarchitectures were synthesized by hydrothermal method. • The formation mechanisms of different microstructures were proposed. • The as-prepared products show morphology-sensitive photoluminescent properties. [ABSTRACT FROM AUTHOR]

The magnetic and magnetocaloric properties of Mn1.1Fe0.9P1-xGex compounds with x = 0.20, 0.22, 0.23, 0.26, and 0.30 have been investigated. In the composition range x from 0.20 to 0.30, the compounds crystallize in the Fe2P-type hexagonal structure. The Curie temperature of the compounds strongly increases with increasing Ge contents. A history dependence of the magnetic phase transition is observed in this compound system. The optimum composition range and the temperature range of the Mn1.1 Fe0.9P1-xGex compounds for magnetic refrigeration applications have been determined. In the composition range x from 0.20 to 0.23, the compounds exhibit large magnetic-entropy change in a low magnetic field. [ABSTRACT FROM AUTHOR]

Abstract: We present a description of the critical behavior at the first-order phase transition in MnFeP1− x As x system in terms of the Bean–Rodbell model. Within the molecular-field approximation, the Gibbs free energy of the system is expressed in terms of the exchange interaction, the elastic energy, the entropy term, the pressure term and the Zeeman energy. A magnetic-state equation has been obtained by minimizing the Gibbs free energy with respect to the volume and the magnetization. The characteristic parameters for the phase transition observed in this system have been obtained by fitting our experimental data. The results show that the magnetoelastic coupling plays a very important role in the mechanism of the phase transition. [Copyright &y& Elsevier]

Reports the discovery of a large magnetic entropy change in MnFeP[sub 0.45]As[sub 0.55]. Demonstration of magnetic refrigeration techniques based on the magnetocaloric effect (MCE); Alignment of randomly oriented magnetic moments by an external magnetic field; Removal of heat from the MCE material to the ambient atmosphere by heat transfer.

Provides information on a study that examined the magnetic properties of the compound, HoTiGe by means of magnetization measurements at different temperatures and fields. Experimental details; Results and discussion on the study.

Abstract Nanocrystalline NbB 2 powder has been synthesized via a single step solid-state reaction of precursor materials Nb 2 O 5 and NaBH 4. Phase composition, grain morphology, microstructure, phonon vibrations and superconducting properties were investigated by XRD, FESEM, HRTEM, Raman spectroscopy and PPMS. The results show that the grain size of nanocrystalline NbB 2 is very sensitive to the reaction temperature and easy to aggregate to form micron scale of non-morphology powders. A systematic increase of the electron-phonon coupling constant with the nanoscaling grain size is observed, which we explain in terms of crystal defects and phonon vibrations. The zero-temperature critical fields, H c 1 (0) and H c 2 (0), have been estimated at 85 Oe and 7200 Oe, respectively, and the Ginzburg–Landau parameter κ is 5.1, confirming that NbB 2 is a type-II superconductor. Highlights • Single-phased NbB 2 nanocrystalline has been synthesized by a solid-state reaction in a continuous evacuating process. • The reaction temperature has an important effect on the grain size. • A systematic increase of the electron-phonon coupling constant with the nanoscaling grain size is observed. [ABSTRACT FROM AUTHOR]

Presents a study which measured the dependence on magnetic filed and temperature of the electrical resistance and magnetization of manganese iron phosphide[sub0.55]arsenide[sub0.45] which undergoes a reversible first-order ferromagnetic-to-paramagnetic phase transition. Experimental procedure; Results and discussion; Conclusion.

Review: 38 refs. [ABSTRACT FROM AUTHOR]

We have studied the magnetocaloric effect in MnFe(P,Si,Ge) compounds. The structural properties of the compounds were determined by x-ray diffraction. The homogeneity and the stoichiometry of the compounds were checked by electron probe microanalysis. The Curie temperature is found to be near room temperature. Specific-heat measurements made on these compounds show a first-order ferromagnetic—paramagnetic phase transition. The magnetocaloric effect derived from magnetization data shows that this effect in the MnFe(P,Si,Ge) compounds is as large as that in Gd-based compounds and MnFeP1-xAsx compounds. This means that we have succeeded in totally replacing As by (Ge,Si) in the latter compounds without losing the favorable magnetic properties. The upshot is that we have found relatively low cost and nontoxic materials for room-temperature cooling applications. [ABSTRACT FROM AUTHOR]

One important aspect of the magneto-structural transition in MnCoGe-based materials is the reduction in saturation magnetization from the orthorhombic to the hexagonal phase. Here, by combining an element specific magnetization probe such as x-ray magnetic circular dichroism and band structure calculations, we show that the magnetic moment instability between orthorhombic and hexagonal structures originates from a reduction in the Mn sub-lattice magnetization. [ABSTRACT FROM AUTHOR]

Nanocrystalline Eu-doped PrB 6 ultrafine powders have been successfully fabricated through solid-state chemical reaction of Eu 2 O 3 , PrCl 3 and NaBH 4 as raw materials. The optical absorption properties of the synthesized samples were investigated by experimental measurement and theoretical calculation. As a result, a strong red-shift of transmittance wavelength of nanocrystalline PrB 6 is achieved via altering the Eu doping. Theoretically, the doping of divalent Eu into trivalent PrB 6 reduces the plasma frequency excitation energy and increases the corresponding transmittance wavelength. Additionally, the synchrotron radiation absorption shows that Pr and Eu atoms exist in the form of Pr3+ in PrB 6 and Eu2+ in EuB 6 , and X-ray photoelectron spectroscopy results also indicate that Eu exists in the state of Eu2+ in the nanocrystalline Pr 0.4 Eu 0.6 B 6 , which confirms that the Eu doping reduces the number of conduction electrons in PrB 6 and decreases the plasma frequency excitation energy. [ABSTRACT FROM AUTHOR]

Recent studies have pointed out that first-order magnetic transitions can be affected by defects. It however remains unclear which precise microstructural features are involved and how to pragmatically control their formation. Here, we show that a genuine technical parameter such as the compaction pressure employed prior to the sintering can induce subtle differences on magnetization data and yet correspond to a large evolution of the magnetocaloric performances in MnFe 0.95 P 0.575 Si 0.36 B 0.065 compounds prepared by powder metallurgy, resulting in an enhancement of the isothermal entropy change (Δ S) in 1 T up to ∼40 %. This outcome is unexpected as Δ S normalized per mass should not be affected by what is at first glance a matter of compaction or density. Our detailed structural and microstructural investigations indicate that the sharpening of the transition for the highest compaction pressures originate from different distributions of the secondary phase at the grain boundaries. This work not only bring into light an interesting fundamental question how microstructural details can affect the development of a magnetic transition, it has also important practical consequences to ensure a reproducibility of large magnetocaloric or thermomagnetic effects in MnFe(P,Si,B) materials for possible applications. [Display omitted] • Magnetocaloric performances of MnFe(P,Si,B) increase with higher green compaction. • Final density not affected by green pressure with common 24 h high temperature sintering. • Increase in ΔS is not related to secondary phase content but rather to its distribution. [ABSTRACT FROM AUTHOR]

High field X-ray powder diffraction and magnetization measurements were carried out for MnFePGe in order to investigate the magnetic field effect on the structural property. A field-induced anisotropic lattice deformation was observed, accompanied by the metamagnetic transition from the paramagnetic to the ferromagnetic states in the vicinity of the Curie temperature of 285 K. In this deformation at 280 K, the lattice parameter a expands by 1.2 % whereas the parameter c contracts by 2.7 %. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic and electrical transport behaviors of Cr3(Se1−x Te x )4 compounds are investigated. A transition from antiferromagnetism to ferromagnetism occurs at x =0.2 in this system and abnormal changes of the lattice parameter a and angle β take place around the magnetic transition point. When Se is partially substituted by Te, a minimum of resistivity (ρ min) is observed in the temperature dependence of resistivity. The temperature T min, where the minimum ρ min is, increases with Te concentration. The minimum in resistivity at T min is ascribed to the competition between a diminishing resistivity due to domain ordering and a rising resistivity due to disordered frozen spins in each domain. The electrical transport behavior below T min is described by hopping conductivity in terms of variable range—hopping. An external magnetic field affects strongly the resistivity of the Cr3(Se1−x Te x )4 compounds, which shifts the magnetic ordering temperature T MO to higher temperature and T min to lower temperature. Subsequently, a negative magnetoresistance is found in this system. [Copyright &y& Elsevier]

The structural and magnetic properties of Sm2Co17-xCrx (0≤x≤3.0) compounds have been investigated by means of X-ray diffraction and magnetization measurements. The powder X-ray diffraction patterns show that all samples crystallize as a single phase with the rhombohedral Th2Zn17-type structure. The lattice parameters a and V increase monotonically with increasing Cr content, but the lattice parameter c increases very slowly with increasing Cr content. The X-ray diffraction patterns of the aligned powder of the samples have confirmed that all the compounds investigated have uniaxial anisotropy. The Curie temperature of the compounds decreases rapidly the spontaneous magnetization M0, the anisotropy field Ba, and the anisotropy constant K1 of Sm2Co17-xCrx (0≤x≤3.0) compounds decrease strongly with increasing Cr content. [Copyright &y& Elsevier]

Fe2MnSi1−xGex (x=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1) compounds were prepared by a mechanically activated solid-state diffusion method. Both X-ray diffraction and differential scanning calorimetry evidenced the presence of an amorphous phase after 10 h of milling. The X-ray data reveal that in the high-temperature annealing the single D03-type phase can be retained up to 50% substitution of Ge for Si in Fe2MnSi. A metastable D03 phase is obtained after crystallization of the as-milled amorphous compounds with x>0.5. High-temperature annealing transforms the low-temperature D03 phase into a single D019 phase (x=1) or a mixture of D03 and D019 phase (x=0.6 and 0.8). Low-field thermomagnetic measurements show a moderately sharp ferromagnetic-paramagnetic transition, which becomes enormously broad in higher magnetic fields. The Curie temperature is significantly enhanced when going from the D03 phase to the D019 phase. Neither a magnetic-field-induced transition nor a reversible structural transition is observed throughout this compound series. The magnetocaloric effect associated with the magnetic transition is small. [Copyright &y& Elsevier]

We synthesized for the first time the intermetallic compound Fe2MnGe. To avoid preferential evaporation of volatile components we exploited mechanical alloying. Amorphous Fe2MnGe alloy powder was prepared by planetary ball milling elemental starting materials. The amorphous-to-crystalline transition was studied by means of differential scanning calorimetry (DSC) and X-ray diffraction (XRD). A cubic D03 phase is formed at low temperature and transforms to a high-temperature hexagonal D019 phase. The apparent activation energy was determined by means of the Kissinger method. [Copyright &y& Elsevier]

The magnetic phase transitions and the magnetocaloric properties of the pseudo binary system Mn5−xFexSi3 with x=0, 1, 2, 3, 4, 5 have been investigated by measuring the magnetisation as a function of temperature and magnetic field. With increasing Fe content, the antiferromagnetic ordering temperature shifts to higher temperatures. The compound Mn5Si3 is an antiferromagnet with a field-induced transition. At 4.2 K, the Mn5−xFexSi3 compounds with x=1 and 2 display antiferromagnetic behavior up to 38 T. For the compounds with x=4 and 5 we find ferromagnetic order. The magnetic-entropy changes in this system are derived from the temperature and field dependence of the magnetization by means of the thermodynamic Maxwell relation. For the MnFe4Si3 compound, enhanced but modest magnetic-entropy changes are observed. [Copyright &y& Elsevier]

Abstract: We report on magnetic properties and magnetocaloric effects of Mn5Ge3−x Si x alloys with x =0.1, 0.3, 0.5, 1.0, 1.5 and 2.0. All Mn5Ge3−x Si x compounds crystallize in the Mn5Si3–type hexagonal structure with space group P63/mcm. The lattice parameters and the Curie temperature of Mn5Ge3−x Si x alloys decrease with increasing x. A considerable large magnetic-entropy change has been observed in these alloys near room temperature. Typical values are 2.3 and 7.8J/kgK at T c =299K for magnetic field changes from 0 to 1T and from 0 to 5T, respectively. The average Mn magnetic moment decreases with increasing Si content. The substitution of Si in Mn5Ge3 does not result in a change of the crystal structure. But the Si substitution has two kinds of effects on the magnetocaloric effects. One is that the magnetic-entropy change decreases with increasing Si content, the other one is that the magnetocaloric effect peak becomes broadened. [Copyright &y& Elsevier]

We report on the crystal structure and the magnetic properties of Mn5Sn3-xGax alloys with x = 0.1, 0.3, 0.5, 1.0, and 1.5, which were investigated by means of X-ray powder diffraction and magnetization measurements in fields up to 5 T in the temperature range 5 to 360 K. These alloys have in common that they exhibit a temperature-induced ferrimagnetic phase transition. The results indicate that all samples crystallize in the hexagonal Ni2 In-type structure with space group P63/mmc. The lattice parameters a and c of the Mn5Sn3-xGax decrease with increasing x, while the Curie temperature of these alloys increases with increasing x. All of the alloys exhibit a moderate magnetocaloric effect. Typical values are about 0.8 and 3 J/kgK at Tc = 282 K for x = 1.5 in a magnetic field change from 0 to 1 T and 0 to 5 T, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The phase formation and the magnetic properties of YFe12− x Nb x compounds have been investigated by means of X-ray diffraction and magnetization measurements. The powder X-ray diffraction patterns show that all compounds investigated crystallize single phase in the tetragonal ThMn12-type of structure. The lattice parameters and the unit-cell volume increase slightly with increasing Nb content, but the Curie temperature does not change. The X-ray-diffraction patterns of aligned powders of the samples show that all the compounds investigated have uniaxial anisotropy at room temperature. At 1.5K, the spontaneous magnetization, the anisotropy field and the anisotropy constant K 1 decrease with increasing Nb content. [Copyright &y& Elsevier]

We have studied the magnetic properties of Mn5Ge3−xSbx compounds with x=0, 0.1, 0.2 and 0.3 by means of magnetisation measurements at different temperatures and fields up to 5 T. The compounds crystallize in the hexagonal Mn5Si3-type structure with space group P63/mcm. The compounds show enhanced Curie temperatures but decreasing average magnetic Mn moments with increasing Sb content. The magnetic entropy changes in these compounds are determined from the temperature and field dependence of the magnetisation using the thermodynamic Maxwell relation. Mn5Ge3 exhibits considerably large magnetic entropy changes that are comparable with that of Gd metal. The Sb substitution has two kinds of effects on the magnetocaloric effect (MCE) of Mn5Ge3−xSbx. One is the magnetic entropy change that decreases with increasing Sb content, the other is the MCE peak that becomes broadened. [Copyright &y& Elsevier]

From an energy-saving perspective, solar heat shielding materials for architectural or automobile glass have become more and more important for sustainable development, which has attracted global attention. The solar heat shielding materials need to meet the requirements of high visible transmittance, strong near infrared absorption, low cost and easy process. Nanostructured rare-earth hexaborides and tungsten bronzes are new kinds of promising heat shielding materials with excellent properties. This review presents a brief introduction on the recent progress in these two kinds of materials. Systematic work including the synthesis, characterization and optical response of nanocrystalline rare-earth hexaborides and tungsten bronzes are summarized. Especially the theoretical explanations of the mechanism of optical properties, tunable characteristic of optical properties, influence of particle size and shape on its optical response are reviewed in this document. Finally, we offer some suggestions for further investigation on these nanostructures, including efficient preparation methods considering environmental and economic costs for obtain morphology and size controllable samples; preventing agglomeration of the final products; some problems to be solved for commercial application. The review can provide a quick reference and overview for heat shielding materials and smart window industry. [ABSTRACT FROM AUTHOR]

We explore the crystal structure and magnetic properties of quaternary materials deriving from the hexagonal Fe 2 P, an iron binary known to present a particularly large magnetocrystalline anisotropy potentially interesting for permanent magnets, but with unfortunately a Curie temperature far too low for applications. Using simultaneous metal and metalloid substitutions in Fe 2- z Co z P 1- x B x and Fe 2- z Co z P 1- y Si y quaternaries, we found it is possible to increase the Curie temperature up to at least 640 K while maintaining a c axis uniaxial magnetocrystalline anisotropy, leading to an appreciable magnetic anisotropy at room temperature. In Fe 2-z Co z P 1- x B x , though boron is appropriate to increase the Curie temperature, its amount is limited as it also favors the formation of secondary phases. Contrary to what could be anticipated from the phase diagrams of Fe 2- z Co z P or Fe 2 P 1- y Si y ternaries, simultaneous Co for Fe and Si for P substitutions in Fe 2- z Co z P 1- y Si y are found to significantly expand the range of stability of the Fe 2 P-type crystal structure. X-ray diffraction patterns on powders oriented in magnetic field indicate a c axis uniaxial magnetic anisotropy. Appropriate heat-treatments and slight metal deficiency are found suitable to limit the formation of unwanted secondary phase with 3:1 metal:metalloid ratio. As a result, nearly single-phase Fe 1.95- z Co z P 1- y Si y materials are prepared and exhibit an appreciable magnetic anisotropy with K 1 up to approximately 0.93 MJm−3 at room temperature. This study experimentally demonstrates that Fe 2 P-type transition metal quaternaries can present an interest not only for their first-order magnetic transition, but also for their magnetic anisotropy making them potential candidates for magnetostatic applications. Image 1 • A sizable magnetic anisotropy is obtained in Fe 2 P-quaternaries at room temperature. • Phase diagrams and structure-properties relations of Fe 2 P-quaternaries are explored. • Fe 2- z Co z P 1- y Si y alloys preserve an Fe 2 P-type crystal structure up to y ∼0.6. • Fe 2- z Co z P 1- y Si y alloys present high Curie temperature and uniaxial anisotropy. • Fe 1.8 Co 0.2 P 1- x B x alloys are synthesized, but B content is limited to x ∼0.12 [ABSTRACT FROM AUTHOR]

Employing the short-chain C 4 H 9 NH 3 X (X = Cl, Br, I) compound as the unique capping agent, highly quality CH 3 NH 3 PbX 3 (X = Cl, Br, I) perovskite quantum dots can be synthesized at room temperature in the open air, which possess high photoluminescence quantum yields and tunable emission in the range of 440–660 nm. Besides, C 4 H 9 NH 3 Br can also improve the morphology of CH 3 NH 3 PbBr 3 thin films by spin-coating the N, N -dimerthylformamide solution of CH 3 NH 3 Br, C 4 H 9 NH 3 Br and PbBr 2 , making the thin film dense and compact, and improving its optical properties. Image 1 [ABSTRACT FROM AUTHOR]

Abstract An unconventional phenomena is observed at the first-order magnetic transitions in (Mn,Fe) 2 (P,Si) materials. Here, we show that the first crossing of the transition upon cooling is associated with an abnormal temperature increase. While differential scanning calorimetry can detect this recalescence-like event, purposely-designed probes were employed to quantify it. Recalescence at a magnetic transition is extremely rare. But in (Mn,Fe) 2 (P,Si), it is even more remarkable by its amplitude, with the temperature rising up to +4.0 K. In (Mn,Fe) 2 (P,Si), this phenomenon is associated with irreversible burst-like evolution of the microstructure (increase in defect concentration and micro-cracking) and of the crystal structure. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Fe 2 P-based materials are attracting great interest for their giant magnetocaloric effect making them highly promising candidates for a new energy efficient-magnetic cooling technology. In light of recent results reported in the MnFe(P,Si) and MnFe(P,Si,B) series, here we revisit the effect of Ge substitution for P. By fixing the Mn/Fe ratio to unity while exploring a large range of Ge content, we isolate the effect Ge plays as metalloid element. In contrast to other metalloids (like Si, B or As), Ge substitution for P is found to spectacularly increase the Curie temperature, while preserving the first-order character of the transition. As a consequence, Ge substitution for P provides a mean to achieve giant magnetocaloric performances up to high temperatures (at least 465 K). In addition, the moment formation in MnFe(P,Ge) is investigated using an element specific and orbital selective magnetization probe, x-ray magnetic circular dichroism. The magnetic moments carried by Mn atoms are found to be significantly larger than that of Fe, providing a direct experimental support to reported band structure calculations and neutron diffraction experiments. [ABSTRACT FROM AUTHOR]

MnFeP1-xSix compounds with x=0.10,0.20,0.24,0.28,...,0.80,1 were prepared by high-energy ball milling and solid-state reaction. The structural, magnetic, and magnetocaloric properties are investigated as a function of temperature and magnetic field. X-ray diffraction studies show that the samples in the range from x=0.28 to 0.64 adopt the hexagonal Fe2P-type structure with a small amount of second phase which increases with increasing Si content. The samples with lower Si content show the orthorhombic Co2P-type structure. Magnetic measurements show that the paramagnetic-ferromagnetic transition temperatures range from 214 to 377 K. Of much importance is the fact that these compounds do not contain any toxic components and exhibit excellent magnetocaloric properties. [ABSTRACT FROM AUTHOR]

3D hierarchical GdPO 4 ·H 2 O:Ln 3+ (Ln 3+  = Eu 3+ , Ce 3+ , Tb 3+ ) flower clusters were successfully prepared on glass slide substrate by a simple, economical hydrothermal process with the assistance of disodium ethylenediaminetetraacetic acid (Na 2 H 2 L, where L 4−  = (CH 2 COO) 2 N(CH 2 ) 2 N(CH 2 COO) 2 4− ). In this process, Na 2 H 2 L was used as both a chelating agent and a structure-director. The hierarchical flower clusters have an average diameter of 7–12 μm and are composed of well-aligned microrods. The influence of the molar ratio of Na 2 H 2 L/Gd 3+ and reaction time on the morphology was systematically studied. A possible crystal growth and formation mechanism of hierarchical flower clusters is proposed based on the evolution of morphology as a function of reaction time. The self-assembled GdPO 4 ·H 2 O:Ln 3+ superstructures exhibit strong orange-red (Eu 3+ , 5 D 0  →  7 F 1 ), green (Tb 3+ , 5 D 4  →  7 F 5 ) and near ultraviolet emissions (Ce 3+ , 5d →  7 F 5/2 ) under ultraviolet excitation, respectively. This study may provide a new channel for building hierarchically superstructued oxide micro/nanomaterials with optical and new properties. [ABSTRACT FROM AUTHOR]