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The crystal structure of novel Sm 26 Co 11 Ga 6 -type {Gd - Er} 26 Ni 6.5-8 Ga 10.5-9 compounds (space group P 4/ mbm , N 127, tP 86) has been established using powder X-ray diffraction. The magnetic ordering and magnetocaloric effect of polycrystalline Er 26 Co 9 Ga 8 , Tb 26 Ni 8 Ga 9 and Tb 26 Co 9.4 Ga 7.6 have been investigated using magnetic and heat capacity measurements. Er 26 Co 9 Ga 8 and Tb 26 Ni 8 Ga 9 show mixed ferro-antiferromagnetic ordering and remarkable permanent magnet properties at low temperatures. Er 26 Co 9 Ga 8 exhibits a large magnetocaloric effect with magnetic entropy change of −11.8 ​J/kg⋅K at 12 ​K and adiabatic temperature of 9.6 ​K for a field change of 50 ​kOe. The 'Gd 26 Ni 8 Ga 9 ' alloy is composed of 88 ​wt% of Gd 26 Ni 8 Ga 9 and 12 ​wt% of GdNi which are both soft ferromagnetic. Due to their close Curie temperatures, the composite of Gd 26 Ni 8 Ga 9 and GdNi displays a table-like magnetocaloric effect with a wide temperature range from 68 ​K to 103 ​K. The crystal structure of novel Sm 26 Co 11 Ga 6 -type {Gd - Er} 26 Ni 6.5-8 Ga 10.5-9 compounds (space group P 4/ mbm , N 127, tP 86) has been established using powder X-ray diffraction. The magnetic ordering and magnetocaloric effect of polycrystalline Er 26 Co 9 Ga 8 , Tb 26 Ni 8 Ga 9 and Tb 26 Co 9.4 Ga 7.6 have been investigated using magnetic and heat capacity measurements. Er 26 Co 9 Ga 8 and Tb 26 Ni 8 Ga 9 show mixed ferro-antiferromagnetic ordering and remarkable permanent magnet properties at low temperatures. Er 26 Co 9 Ga 8 exhibits a large magnetocaloric effect with magnetic entropy change of −11.8 ​J/kg⋅K at 12 ​K and adiabatic temperature of 9.6 ​K for a field change of 50 ​kOe. The 'Gd 26 Ni 8 Ga 9 ' alloy is composed of 88 ​wt% of Gd 26 Ni 8 Ga 9 and 12 ​wt% of GdNi which are both soft ferromagnetic. Due to their close Curie temperatures, the composite of Gd 26 Ni 8 Ga 9 and GdNi displays a table-like magnetocaloric effect with a wide temperature range from 68 ​K to 103 ​K. [Display omitted] • Er 26 Co 9 Ga 8 and Tb 26 Ni 8 Ga 9 show mixed F-AF ordering below 12 ​K and 82 ​K. • They exhibit permanent magnet properties at low temperatures. • MCE of Tb 26 Co 9.4 Ga 7.6 , Er 26 Co 9 Ga 8 , Gd 26 Ni 8 Ga 9 and Tb 26 Ni 8 Ga 9 are investigated. • Er 26 Co 9 Ga 8 shows largest adiabatic temperature due to low heat capacity. • Two-phase 'Gd 26 Ni 8 Ga 9 ' show a table-like MCE from 68 ​K to 103 ​K. [ABSTRACT FROM AUTHOR]

The magnetic ordering of polycrystalline Ho 6 Co 2 Ga-type Gd 6 Co 2.2 Al 0.8 , Tb 6 Co 2.2 Al 0.8 , Tb 6 Co 2 Al and Dy 6 Co 2.2 Al 0.8 (space group Immm , N 71, oI 36) has been established using magnetic measurements and the magnetic structure of Tb 6 Co 2.2 Al 0.8 has been resolved by the neutron diffraction study. Gd 6 Co 2.2 Al 0.8 exhibits field sensitive ferro-antiferromagnetic ordering, meanwhile Tb 6 Co 2.2 Al 0.8 , Tb 6 Co 2 Al and Dy 6 Co 2.2 Al 0.8 are antiferromagnets with metamagnetic transformation of magnetic ordering. Gd 6 Co 2.2 Al 0.8 is soft ferromagnet, whereas Tb 6 Co 2.2 Al 0.8 , Tb 6 Co 2 Al and Dy 6 Co 2.2 Al 0.8 exhibit low-temperature weak permanent magnet properties. From these compounds, Gd 6 Co 2.2 Al 0.8 demonstrates largest magnetocaloric effect with magnetic entropy change of −10.89 J/kg⋅K at 75 K for a field change of 50 kOe (relative cooling power of ~760 J/kg). Neutron diffraction study indicates non-collinear abc -antiferromagnetic ordering of Tb 6 Co 2.2 Al 0.8 in zero applied magnetic field. Below 63 K and down to 52 K, Tb 6 Co 2.2 Al 0.8 exhibits antiferromagnetic ordering with magnetic space group I′22′2′ (wave vector K 0 = [0, 0, 0]). Below 52 K and down to 1.5 K, the magnetic structure of Tb 6 Co 2.2 Al 0.8 is sum of magnetic component with P2 1 ′2 1 2′ magnetic space group (wave vector K 0 = [0, 0, 0]) and square-modulated antiferromagnetic component along c -axis of unit cell with K 1 = [±1/4, 0, ±1/4] wave vector. Image 1 • Gd 6 Co 2.2 Al 0.8 shows F-AF ordering and it is soft ferromagnet down to 2 K. • Δ S m of Gd 6 Co 2.2 Al 0.8 reaches of −10.89 J/kg⋅K at 75 K in field change of 50 kOe. • Tb 6 Co 2.2 Al 0.8 , Tb 6 Co 2 Al and Dy 6 Co 2.2 Al 0.8 show field sensitive AF ordering. • Tb 6 Co 2.2 Al 0.8 , Tb 6 Co 2 Al and Dy 6 Co 2.2 Al 0.8 are LT weak permanent magnets. • Tb 6 Co 2.2 Al 0.8 exhibits abc -Antiferromagnetic ordering in zero applied field. [ABSTRACT FROM AUTHOR]

• Change of ions tunes the magnetocaloric effects in the range 2–400 K. • 2 Direct MCE with a table-like effect in-between, interesting for Ericsson cycle. • Inverse MCE at low temperatures. • PM-FM transition ruled by long-range magnetic interactions. The structural, magnetic, magnetocaloric (MCE) and thermal properties of seven Fe 2 P-type Dy 6 (Fe,Mn)X 2 (X Sb, Bi, Te) intermetallics (space group P 6 ¯ 2 m , N 189, hP9) have been experimentally studied. They present a paramagnetic to ferromagnetic transition (in the range 129–370 K), followed, as temperature decreases, by a spin-reorientation one (from 52 to 170 K) and a ground magnetic state at 2 K with antiferromagnetic components. This state turns into a ferromagnetic state when a magnetic field is applied. The critical exponents β,γ,δ related to the PM-FM transition point to long range order interactions but in most compounds their values severely deviate from the Mean Field class, presenting an unconventional critical behavior, probably due to magnetocrystalline anisotropies. This magnetic complexity has the consequence that in every intermetallic three MCE effects arise: Two direct magnetocaloric effects (DMCE) with a table-like effect in between (from 40 K to more than 400 K), with moderate values of the magnetic entropy maxima (up to 6.9 J/kgK for μ 0 Δ H = 5 T, with the tableau in-between being around 4 J/kgK, for Dy 6 FeSb 2 and Dy 6 FeSbTe). The calculation of the Thermal Average Entropy Change allows to place the properties of two compounds (Dy 6 FeSb 2 and Dy 6 FeSbTe) close to other rare earth based high entropy alloys described in literature. The seven compounds present a relevant third MCE, inverse, below 25 K, with a value as high as 17.8 J/kgK (μ 0 Δ H = 5 T) for Dy 6 FeSbTe. The maximum of the magnetic entropy change at the Curie temperature has been shown to scale with the critical exponents found and universal curves have been built. Finally, the thermal diffusivities in the range of the DMCE have been measured, with the result that they present good values (between 1 and 3 mm2/s) to be used in real magnetocaloric refrigeration systems. [ABSTRACT FROM AUTHOR]

The partial isothermal sections of {Gd, Ho}-Ni-Te and Gd-Co-Te systems (~40–100 ​at. % of rare earth) have been investigated at 1070 ​K by X-ray and electron microprobe analysis. The Y 5 Ni 2 Te 2 -type {Tb, Dy, Ho} 5 Fe 2 Te 2 and {Gd, Tb, Dy, Ho} 5 {Co, Ni} 2 Te 2 (space group Cmcm , No. 63, oC 36), Er 7 Ni 2 Te 2 -type Er 7 Co 2 Te 2 , {Y, Dy, Ho} 7 Ni 2 Te 2 , Ho 7 {Rh, Pd} 2 Te 2 and {Y, Gd} 7 Pt 2 Te 2 (space group Imm 2, No. 44, oI 22), Fe 2 P-type Ho 6 NiTe 2 (space group P -62 m , No. 189, hP 9) and Sc 6 PdTe 2 -type Ho 6 {Rh, Pd}Te 2 and {Y, Gd} 6 PtTe 2 (space group Pnma , No. 62, oP 36) compounds have been established using powder X-ray diffraction studies. Magnetization measurements show that the Y 5 Ni 2 Te 2 -type {Tb, Dy, Ho} 5 Fe 2 Te 2 , {Gd, Tb, Dy} 5 Co 2 Te 2 and {Tb, Ho} 5 Ni 2 Te 2 compounds exhibit a high-temperature ferromagnetic ordering with low-temperature spin-reorientation transition for Tb-, Dy- and Ho-containing compounds. Below Curie temperature, Tb 5 Fe 2 Te 2 , Tb 5 Co 2 Te 2 and Ho 5 Ni 2 Te 2 are soft ferromagnets, while they show hard magnetic properties below spin-reorientation transition. At 2 ​K, Tb 5 Co 2 Te 2 and Tb 5 Fe 2 Te 2 exhibit a coercive field of 35 ​kOe and ~30 ​kOe and the residual magnetization of 17.2 μ B and 22.9 μ B per formula unit, leading to theoretical maximum energy product of ~620 ​kJ/m3 and ~700 ​kJ/m3, respectively. Ho 5 Ni 2 Te 2 reaches a maximum magnetic entropy change of −10.0 ​J/kg⋅K and −9.4 ​J/kg⋅K for a magnetic field change of 0–50 ​kOe ​at 45 ​K and 20 ​K, respectively. Image 1 • Partial {Gd, Ho}-Ni-Te and Gd-Co-Te isothermal sections were obtained at 1070 ​K. • Twenty four new ternary compounds were found in Rare earth-{Fe,Co,Ni,Rh,Pd,Pt}-Te systems. • They are Y 5 Ni 2 Te 2 -, Er 7 Ni 2 Te 2 -, Fe 2 P- and Sc 6 PdTe 2 -type compounds. • Y 5 Ni 2 Te 2 -type {Gd,Tb,Dy,Ho} 5 {Fe,Co,Ni} 2 Te 2 exhibit ferromagnetic type of ordering. • Ho 5 Ni 2 Te 2 shows large MCE, while Tb 5 {Fe, Co} 2 Te 2 are giant LT permanent magnets. [ABSTRACT FROM AUTHOR]

The magnetic and magnetocaloric properties of the intermetallic family (Gd,Tb) 6 (Fe,Mn)Bi 2 have been studied from 2 K to temperatures above the respective Curie temperatures T C. The substitution of Gd by Tb (Gd 6 FeBi 2 , Gd 3 Tb 3 FeBi 2 , Tb 6 FeBi 2) tunes T C in the range 350-250 K and favors the apparition of a metamagnetic transition at very low temperature (below 10 K) from a complex magnetic state to a ferromagnetic one, as well as a spin reorientation transition below T m = 72 K. As a consequence, an important inverse magnetocaloric effect (IMCE) appears below 20 K and an interesting direct magnetocaloric effect (DMCE) appears over a wide temperature span between T C and T m with maxima at those temperatures. The partial substitution of Fe by Mn in Tb 6 Fe 0.5 Mn 0.5 Bi 2 shifts these effects upwards in temperature while expanding the region of the direct magnetocaloric effect between 70 and 400 K. The combination of adjoint IMCE and DMCE as well as the wide span of the latter shows that tuning this family allows to locate the magnetocaloric effect in different regions of interest. The critical behavior of the PM-FM transitions has been studied obtaining the critical exponents α, β, γ, δ and checking that the respective magnetocaloric effects also scale with the critical parameters n and δ. The transition in Gd 6 FeBi 2 belongs to the Heisenberg universality class with deviations due to magnetocrystalline anisotropies; the critical exponents for Gd 3 Tb 3 FeBi 2 (in agreement with the Mean Field model) suggest the presence of long range order magnetic interactions, while Tb 6 FeBi 2 and Tb 6 Fe 0.5 Mn 0.5 Bi 2 present an unconventional critical behavior aligned with long range order interactions. • Gd by Tb substitution tunes T C and improves the magnetocaloric properties. • Tb samples present two main transitions and extended temperature working range. • Adjoint inverse and direct magnetocaloric effects in Td-doped compounds. • Critical exponents α, β, γ, δ found for the PM-FM transition. [ABSTRACT FROM AUTHOR]

Four polycrystaline Fe 2 P-type Ho 6 (Fe,Mn)Bi 2 intermetallic compounds (space group P 6 ‾ 2 m , No. 189, hP 9) have been studied using magnetic techniques in order to explore their ability as magnetocaloric materials, and study the critical behavior of the paramagnetic (PM) to ferromagnetic (FM) transitions to obtain a deeper understanding of the range of the magnetic interactions. The obtained critical exponents β , γ and δ for the four compounds studied (Ho 6 MnBi 2 , Ho 6 FeBi 2 , Ho 6 (Mn 0.5 Fe 0.5)Bi 2 , Ho 6 (Mn 0.75 Fe 0.25)Bi 2) point to long-range order interactions, as they are close to those of the Mean Field Universality class. All of the compounds show relevant magnetocaloric properties over a very broad temperature range, limited by the PM-FM transition and a spin-reorientation one, well separated in all cases. They present very high values of the refrigerant capacities (from 520 J/kg to 709 J/kg at 5 T), good magnetic entropy changes (from 3.4 to 5.7 J/(kgK) at 5 T), and a flat and wide temperature span for the working temperature range (nearly 200 K for Ho 6 MnBi 2 , 80 K for Ho 6 FeBi 2 at 5T). The change in properties with composition proves that the magnetocaloric properties can be tuned in Fe 2 P-type compounds to accommodate different refrigeration applications. Finally, the magnetocaloric scaling laws have been successfully tested and universal curves for the magnetic entropy change have also been obtained in the PM-FM transition region. • Second order FM to PM transition, long-range order interactions involved. • Very high values of the refrigerant capacities from 520 J/kg to 709 J/kg at 5T • Good magnetic entropy changes from 3.4 to 5.7 J/(kgK) at 5T • Flat and wide temperature span for the working temperature range (up to 200 K). • Magnetocaloric scaling laws tested and universal curves obtained. [ABSTRACT FROM AUTHOR]