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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]

• 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]

Review: 38 refs. [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]

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]

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]

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]

The crystal structure, magnetic and magnetocaloric properties of (Mn,Fe,T) 1.95 P 0.50 Si 0.50 (T = Co, Ni and Cu) compounds have been investigated. All the compounds crystallize in the Fe 2 P-type hexagonal structure. All these transition metal substitutions for either Mn(3 g ) or Fe(3 f ) weaken the ferromagnetic ordering, while showing complex effects on the energy barrier for nucleation in the first-order magnetic phase transition and result in complex behaviors in thermal/magnetic hysteresis. A first-principles density functional theory calculations show that Co, Ni and Cu atoms occupy 3 f , 3 f and 3 g sites, respectively. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new preparation method for NaZn13-type La(Fe,Si)13 are reported. [•] When Si content in the range of 2.2 to 2.4, it directly forms the single phase. [•] Magneto-caloric effects show an excellent magnetic refrigeration property. [Copyright &y& Elsevier]

The Mn 38 Fe 22 Al 40 C x alloys with x = 0, 0.1, 0.3, 0.5, 0.7, 1.5 and 2.5 were investigated. XRD results show that the alloys with x = 0, 0.1, 0.3, 0.5, 0.7 crystallize in CsCl(B2)-type structure. The alloys with x = 1.5 and 2.5 crystallize in (Fe/Mn) 3 Al(DO 3 ), and there exists an α-Mn phase. The Curie temperature ( T C ) decreases with increasing of carbon content. The maximal magnetic-entropy change is 0.71 J/kg K (0–1.5 T) for x = 0.3 at 297 K, which is 16% higher than that of the parent alloy. The adiabatic temperature change of Mn 38 Fe 22 Al 40 C x alloys was around 0.19 K in 1.5 T. [ABSTRACT FROM AUTHOR]

The MnFeP0.56Si0.44 compound is investigated by x-ray diffraction, magnetic measurements, and x-ray absorption fine structure spectroscopy. It crystallizes in Fe2P-type structure with the lattice parameters a = b = 5.9823(0) Å and c = 3.4551(1) Å and undergoes a first-order phase transition at the Curie temperature of 255 K. The Fe K edge and Mn K edge x-ray absorption fine structure spectra show that Mn atoms mainly reside at 3g sites, while 3f sites are occupied by Fe atoms. The distances between the absorbing Fe atom and the first and second nearest neighbor Fe atoms in a 3f-layer shift from 2.65 Å and 4.01 Å in the ferromagnetic state to 2.61 Å and 3.96 Å in the paramagnetic phase. On the other hand, the distance between the 3g-layer and 3f-layer changes a little as 2.66 Å–2.73 Å below the Curie temperature and 2.68 Å–2.75 Å above it. [ABSTRACT FROM AUTHOR]