Tailoring the magneto‐structural coupling in magnetic martensitic materials is pivotal for optimizing multifunctional properties such as magnetocaloric effect (MCE) and negative thermal expansion (NTE). This study demonstrates how Ni substitution in Mn 1‐ x Ni x CoGe ( x = 0.03 to 0.07) modulates the magneto‐structural transitions as investigated by in‐situ X‐ray diffraction, magnetization measurements, and geometric compatibility analysis. Ni doping is shown to stabilize the hexagonal phase, lower the martensitic transformation temperature, and introduce intermediate ferromagnetic hexagonal (FM‐Hex) states, thereby altering the transition pathways from a single paramagnetic hexagonal (PM‐Hex) ↔ ferromagnetic orthorhombic (FM‐Orth), to a two‐step PM‐Hex ↔ FM‐Hex ↔ FM‐Orth sequence. This modification in the magneto‐structural coupling alleviates lattice incompatibility, broadens phase transition temperature window, and enhances magnetization changes during the phase transition. The magnetocaloric refrigeration capacity increases from 213(14) J kg −1 for x = 0.04 to 308(18) J kg −1 for x = 0.07 under a 5 T driving field, while the NTE coefficient is tuned from ‐375(1) × 10 −3 K −1 for x = 0.05 to ‐143(1) × 10 −3 K −1 for x = 0.07. These findings provide mechanistic insights into the interplay between magnetization states and lattice compatibility, thereby advancing the design of energy‐efficient solid‐state cooling and precision actuators through controllable magneto‐structural coupling.

The lack of magnetic refrigeration (MR) materials with high magnetocaloric effect (MCE) and large relative cooling power (RCP) in the temperature range required for hydrogen liquefaction (20 K-77 K) is a bottleneck for practical applications of MR cooling systems. The present investigation of TbMn2Si2-xGex compounds (x = 0.1, 0.2) by variable temperature neutron and synchrotron X-ray diffraction, magnetization and heat capacity measurements, establish that substitution of Si with Ge in TbMn2Si2 leads to a significant enlargement of the unit cell and modification of the magnetic properties. Two consecutive ferromagnetic first-order transitions occur below 77 K with the third transition from paramagnetism to a collinear antiferromagnetic state being determined around 500 K. The resultant plateau-like MCE with large RCP below 77 K in these designed compounds offers scope for application for hydrogen liquefaction. Detailed neutron investigation confirm that four magnetic states exist within the temperature range 5 K to 500 K, with two successive first-order magnetic transitions below 77 K responsible for the large MCE. Our specific heat studies provide evidence of strong contributions from the nuclear specific heat and the corresponding nuclear specific heat coefficients of A = 430 +/- 50 mJ mol-1 K and A = 418 +/- 60 mJ mol-1 K have been determined for TbMn2Si2-xGex with x = 0.1 and x = 0.2, respectively. The over-lapping entropy curves near these successive transitions lead to a plateau-like magnetothermal effect as well as a large reversible MCE for both samples (e.g. Delta SMmax = 14.0 J/kg K and Delta Tmax = 7.6 K; RCP = 379 J/kg for TbMn2Si1.9Ge0.1 for an applied field of 5 T) indicating that the material can operate over a wide temperature range - particularly for hydrogen liquefaction.

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The magnetic properties of PrMn 2 Ge 2 samples in both the as-cast bulk and melt-spun ribbon forms have been investigated in detail by a comprehensive set of x-ray and neutron powder diffraction, magnetic and heat capacity measurements and corresponding sets of data analyses. Thermal expansion measurements indicate the presence of magnetoelastic coupling effects around all transition temperatures in the bulk sample. The bulk modulus K 0 = 42.0 GPa and its first derivative K 0 ' = 18.7 have been derived from the pressure -volume data. The Curie temperature from the intralayer antiferromagnetism ( AFl ) of PrMn 2 Ge 2 to a canted spin structure ( Fmc ) is T Cinter = 332 K for the bulk sample, decreasing to T Cinter = 320 K for the ribbon sample. The critical components gamma, beta and delta of this second order magnetic transition as determined from Kouvel-Fisher analyses, indicate long range magnetic interactions around T C inter . Based on these critical exponents the magnetization, field and ( H temperature data around T Cinter collapse onto two curves obeying the single scaling equation M ( H , epsilon ) = epsilon beta f +/- ) . The Debye temperatures and the density of states at epsilon beta + gamma the Fermi level are theta D = 306 K and N ( E F ) = 3 .47 state /eV atom for the bulk sample and theta D = 320 K and ( E F ) = 2 .18 state /eV atom for the ribbon sample with the nuclear specific heat coefficient for bulk PrMn 2 Ge 2 derived from the splitting of the nuclear hyperfine levels as C N = 517 mJ mol - 1 K -1 . With a field change of Delta B = 5 T, the maximum values of the magnetic entropy changes - Delta S max in the region around T Cinter are - Delta S max = 3.00 J/kg K and 2.35 J/kg K for the bulk and ribbon samples respectively, while the relative cooling power (RCP) for the ribbon-spun sample, RCP = 135.9 J/kg, is significantly higher than the value of RCP = 116.6 J/ kg for the bulk sample. These findings indicate that PrMn 2 Ge 2 could be a promising candidate for magnetic refrigeration applications in the room temperature region.

We have investigated the effects of Lu substitution on the magnetic behaviour and ordering of (Ho1-xLux)2Fe2Si2C (x = 0.32 and 0.46) by high-resolution neutron powder diffraction, magnetisation and specific heat over the temperature range 2 to 300 K. Our study has established that the antiferromagnetic (AFM) state is weakened upon Lu substitution and that the N & eacute;el temperature TN shifts towards lower temperature with increasing Lu content. The replacement of the magnetic Ho3+ ion by the non-magnetic Lu3+ ion of smaller atomic radius, leads to a modification of the crystal field levels, as indicated by the specific heat measurements. Neutron diffraction data analysis reveals that the magnetic structure of undoped Ho2Fe2Si2C, which exhibits a commensurate, antiferromagnetic ordering of the Ho sublattice along the b-axis with a propagation vector k = [0, 0, 1 2 ], is maintained in the Lu-doped (Ho1-xLux)2Fe2Si2C compounds.

The structural and magnetic properties of TbMn2-xFexSi2 compounds (x = 0.0-0.4) have been investigated in details by high-resolution synchrotron x-ray and neutron powder diffraction, specific heat, and dc magnetization measurements. The replacement of Fe for Mn in TbMn2-xFexSi2 does not change the crystal structure but leads to a significant contraction of the unit cell (dV/dx similar to - 6 & Aring;(3)) and modification of three magnetic phase transition temperatures - the Curie temperatures T-c1, T-c2 and the N & eacute;el temperature T-N. For example, the T-c1, T-c2 and T-N values of TbMn2Si2 decrease from T-c1 = 50 K, T-c2 = 64 K and T-N = 500 K to T-c1 = 27 K, T-c2 = 37 K and T-N = 440 K for TbMn1.6Fe0.4Si2. Detailed neutron diffraction investigations have allowed us to determine the magnetic structures and construct the magnetic phase diagram as well as confirm the presence of magnetoelastic coupling effects. The significantly different responses of T-c1 and T-c2 to applied magnetic fields (e.g. dT(c1)/dB = 0.52 K/T and dT(c2)/dB = 4.7 K/T for TbMn1.6Fe0.4Si2), leads to expansion of the temperature region (Delta T = T-c2 - T-c1) for the canted ferromagnetic state Fmc-ii between T-c1 and T-c2. In the case of TbMn1.6Fe0.4Si2, Delta T increases from Delta T = 9 K for applied magnetic field B = 0.2 T to Delta T = 36 K for B = 6 T, resulting in plateau-like behaviour of magnetic entropy change and enhances the relative cooling power (RCP) in this system. Under a change of magnetic field of 0 T - 5 T, the maximum value of the magnetic entropy changes -Delta S-max and adiabatic temperature change, Delta T-ad are derived to be -Delta S-max = 13.1 J/kg K and Delta T-ad = 8.4 K with the RCP = 411 J/kg for x=0.4 sample. The plateau-like magnetocaloric effect and relatively large RCP make these materials potentially suitable for application in cryogenic magnetic refrigeration.

The structural and magnetic properties of LaMn2Ge2 compound in both the as-cast bulk and melt-spun ribbon forms have been investigated by a comprehensive set of x-ray/neutron powder diffraction, magnetic and heat capacity measurements as well as corresponding sets of data analyses. Our neutron diffraction study reveals that with decreasing temperature the magnetic state of bulk LaMn2Ge2 changes first from paramagnetic to incommensurate antiferromagnetism AFfs at TN 430 K, and then gives way to incommensurate canted ferromagnetism Fmi below TC similar to 320 K. No noticeable magnetoelastic effect was detected in the temperature dependence of lattice parameters derived from the refinement of the neutron diffraction patterns over the temperature range 5-460 K. Detailed analyses of the magnetic data indicate that the magnetic phase transition around the ferromagnetic transition (TC similar to 320 K) is second order. Under field changes of 2 T and 5 T, the maximum values of magnetic entropy change around the ferromagnetic transition respectively reach -Delta Smax = 1.65 J/kg K and -Delta Smax = 3.26 J/kg K for the bulk sample, compared with -Delta Smax = 1.21 J/kg K and -Delta Smax = 2.60 J/kg K, for the ribbon sample. The magnetic phase transition around TC has been investigated by Kouvel-Fisher analysis and the Modified Arrott Plot method with the critical exponent values indicating that the magnetic interactions in LaMn2Ge2 are long range. Moreover, it was found that the field- and temperature- magnetisation data around TC collapse onto two curves obeying the single scaling equation M(H,epsilon) = epsilon beta f +/- (H/epsilon beta+gamma) for both the bulk and ribbon samples. With a field change of Delta B = 5 T and Delta B = 8 T, the relative cooling power for bulk sample around 320 K is derived to be RCP 115 J/kg and RCP 199 J/kg, respectively. These findings indicate that LaMn2Ge2 could be a promising candidate for magnetic refrigeration applications in the room temperature region. (c) 2022 Elsevier B.V. All rights reserved.

Energy-efficient and environment-friendly solid-state magnetic refrigeration requires materials with extraordinary magnetocaloric properties. We report the plateau-like magnetocaloric effect activated by tripled magnetic cell in layered intermetallic TbMn2-xCoxSi2 compounds, and the consequent large refrigerant capacity. Substitution of Mn with Co significantly modified the magnetic properties evidenced by two successive ferromagnetic first-order transitions and strong magneto-elasticity as well as significant contraction of the unit cell. Detailed neutron diffraction investigations have established the formation of a tripled magnetic unit cell structure at the temperature range between two magnetic transitions. The overlapping entropy curves near the two transition temperatures results in a plateau-like magnetocaloric effect and enhanced refrigerant capacity. Existence of this special magnetic cell also leads to a variety of interesting physical properties, including a significant drop in resistance and pronounced anomalies in the heat capacity, as well as different responses of the two transition temperatures to an applied magnetic field. The impact of the formation of a tripled magnetic cell on the physical properties is highly unusual for magnetic alloys and merits expanded investigation of this class of magnetic materials to explore for novel applications.

The thermal expansion of the rare earth intermetallic compounds Sm3(CoxFe1-x)29-yCry (x = 0.9, y = 7; x = 0.8, y = 6.5; x = 0.7, y = 6) have been systematically investigated by high resolution synchrotron x-ray diffraction measurements (-120-480 K; - 300-823 K). The magnetic and thermal properties of Sm3(Fe0.9Co0.1)24Cr4 have been studied as a typical example of the Sm3(CoxFe1-x)29-yCry system by magnetic measurements (ac susceptibility, - 5-300 K; DC magnetisation, - 77-650 K) and specific heat measurements (-2-300 K). The Debye temperature of Sm3(Co0.9Fe0.1)22Cr7 was found to be theta D = 410 +/- 10 K from analyses of the specific heat data while the density of states at the Fermi level was N(EF) = 5.08 +/- 0. 04 ev- 1 atom-1. A pronounced contribution of the nuclear specific heat of Sm3(Co0.9Fe0.1)22Cr7 is evident below 5 K with the nuclear specific heat coefficient found to be A = 758 +/- 30 mJ mol- 1 K-1. Rietveld analyses of the x-ray diffraction data demonstrate the remarkable magneto-volume anomalies of Sm3(CoxFe1-x)29-yCry around their Curie temperatures TC with negative values of the volume magnetostriction detected below the Curie temperatures and values in the range COs = 1.1 x 10-3 to COs = - 4.3 x 10-3 at 300 K.

The structural and magnetic properties of the rare-earth transition metal compound DyFe11.4Nb0.6 have been investigated over its magnetically order state by variable temperature high resolution synchrotron x-ray diffraction (85 K 650 K) together with ac magnetic susceptibility (10 K 300 K), DC magnetization (300 K 600 K) and heat capacity (2 K 300 K) measurements. The magnetic ordering temperature has been determined to be T-C = 538(5) K while with decreasing temperature, two spin reorientations have been detected around T-sr1 = 265 (+/- 5 K) and T-sr2 = 140(+/- 5) K. The Debye temperature theta(D) = 412(+/- 10) K derived from the specific heat measurements of DyFe11.4Nb0.6 agrees well with the values reported for related compounds, while the density of states at the Fermi level was found to be N(E-F) = 3.8 ev(-1) atom(-1). Refinements of the synchrotron x-ray diffraction patterns indicate the occurrence of magnetoelastic couplings at all three magnetic transitions, the Curie temperature TC and spin reorientation temperatures Tsr(1) and Tsr(2). The linear thermal expansion has been determined over the temperature range 85 K 650 K and substantial magneto-volume effects shown to persist at temperatures up to 596 K, significantly above the Curie temperature. Similarly, the spontaneous volume magnetostriction ros of DyFe11.4Nb0.6 extends to 1.17 T-C, well above the Curie temperature T-C = 538(5) K. The spontaneous volume magnetostriction has the value ros = 1.08 x 10(-2) at 85 K. The properties of such materials offer potential for applications in functional structures.

The thermal expansion properties of the rare earth transition metal compound ErFe11.4Nb0.6 (Curie temperature T-c = 520(10) K) have been investigated in detail by variable temperature high resolution synchrotron x-ray diffraction measurements over the temperature range 300 K-640 K. The findings from the Rietveld analyses reveal significant anomalies in the thermal expansion of ErFe11.4Nb0.6 below the Curie temperature with negative thermal expansion also evident around T-c = 520(10) K. The structural changes that occur around the Curie temperature lead to a spontaneous volume magnetostriction of similar to 6.3 x 10(-3) at 300 K. The minimum values of the linear thermal expansion coefficients aa and ac for ErFe11.4Nb0.6 around T-C are determined to be -3.56 x 10(-6) K-1 and -1.30 x 10(-6) K-1 respectively. Details of the structural features of ErFe11.4Nb0.6 (including Wigner-Seitz cell volumes and average bond lengths for Er atoms (2a site) and Fe atoms (8i, 8j, 8f sites) to neighbouring Fe atoms) that contribute to the thermal expansion behaviour have been investigated in detail. The persistence of finite magnetostriction values lambda(a) and lambda(c) (along the a-axis and the c-axis respectively) and volume magnetostriction us, above the magnetic transition temperature, indicates the likely occurrence of short-range magnetic correlations in this region. (C) 2020 Elsevier B.V. All rights reserved.

The crystal field splitting of YbMn2Si2 has been investigated over the temperature range 5-65 K using inelastic neutron scattering at a wavelength of 2.345 angstrom (resolution 800 mu eV; dynamic range similar to 10 meV). The excitation spectra have been analysed using a crystal field model above and below T-N2, the temperature at which the collinear antiferromagnetic structure AFil transforms to the low-temperature structure in which the magnetic cell is doubled along the c-axis (T-N1 = 526(4) K > T > T-N2 = 32(2) K). The calculated excitation spectra show good agreement with the observed spectra for the unique environment of Yb3+ ions in the collinear antiferromagnetic structure AFil above T-N2 and for the inequivalent sites of Yb3+ ions below T-N2. This agreement has been obtained with a model for the lowtemperature region in which a molecular field with optimal components in the x, y and z directions of B-x = 13.5 T, B-y = 65 T, B-z = 21.3 T is included. The pronounced components in the x and y directions are discussed in relation to the significant contraction of similar to 0.1% of the c lattice parameter below the T-N2 magnetic transition. Crown Copyright (C) 2020 Published by Elsevier B.V. All rights reserved.

The magnetic structures of Er2Fe2Si2C and Tm2Fe2Si2C (monoclinic Dy2Fe2Si2C-type structure, C2/m space group) have been studied by neutron powder diffraction, complemented by magnetization, specific heat measurements, and Er-166 Mossbauer spectroscopy, over the temperature range 0.5 to 300 K. Their magnetic structures are compared with those of other R2Fe2Si2C compounds. Antiferromagnetic ordering of the rare-earth sublattice is observed below the Neel temperatures of T-N = 4.8(2) K and T-N = 2.6(3) K for Er2Fe2Si2C and Tm2Fe2Si2C, respectively. While Er2Fe2Si2C and Tm2Fe2Si2C have the same crystal structure, they possess different magnetic structures compared with the other R2Fe2Si2C (R = Nd, Gd, Tb, Dy, and Ho) compounds. In particular, two different propagation vectors are observed below the Neel temperatures: k = [1/2, 1/2, 0] (for Er2Fe2Si2C) and k = [0.403(1), 1/2, 0] (for Tm2Fe2Si2C). For both compounds, the difference in propagation vectors is also accompanied by different orientations of the Er and Tm magnetic moments. Although the magnetic structures of Er2Fe2Si2C and Tm2Fe2Si2C differ from those of the other R(2)Fe(2)Si(2)Ccompounds, we have established that the two magnetic structures are closely related to each other. Our experimental and first-principles studies indicate that the evolution of the magnetic structures across the R2Fe2Si2C series is a consequence of the complex interplay between the indirect exchange interaction and crystal field effects.

The structural and magnetic properties of DyFe12-xTax compounds (with x = 0.5, 0.6, 0.65 and 0.7) have been investigated in detail using dc magnetization, differential scanning calorimetry, Mossbauer effect spectroscopy (5-300 K) and high-resolution synchrotron x-ray diffraction (10-700 K). The easy magnetization directions at room temperature are along the c-axis. With decreasing temperature, the magneto-crystalline anisotropy changes from easy axis at room temperature to easy cone at T-s(r2) for all compounds, then to easy plane at T-sr1. Both T-sr1 and T-sr(2) change significantly over the ranges 158-216 K and 239-259 K with increasing Ta content (x = 0.5-0.7) respectively, while the Curie temperature is found to remain essentially unchanged with a value of similar to 540 K. Pronounced magneto volume effects have been detected at the Curie temperature while no clear anomalies are observed around the spin reorientation temperatures. Large spontaneous magnetostriction has been detected below T-c for all of the compounds.

Compounds that exhibit the unique behavior of negative thermal expansion (NTE)-the physical property of contraction of the lattice parameters on warming-can be applied widely in modern technologies. Consequently, the search for and design of an NTE material with operational and controllable qualities at room temperature are important topics in both physics and materials science. In this work, we demonstrate a new route to achieve magnetic manipulation of a giant NTE in (Mn0.95Ni0.05)CoGe via strong magnetostructural (MS) coupling around room temperature (∼275 to ∼345 K). The MS coupling is realized through the weak bonding between the nonmagnetic CoGe-network and the magnetic Mn-sublattice. Application of a magnetic field changes the NTE in (Mn0.95Ni0.05)CoGe significantly: in particular, a change of Δ L/ L along the a axis of absolute value 15290(60) × 10-6-equivalent to a -31% reduction in NTE-is obtained at 295 K in response to a magnetic field of 8 T.

R. A. Susilo,1,* X. Rocquefelte,2,† J. M. Cadogan,1 E. Bruyer,2 W. Lafargue-Dit-Hauret,2,3 W. D. Hutchison,1 M. Avdeev,4,5 D. H. Ryan,6 T. Namiki,7 and S. J. Campbell1 1School of Science, UNSW Canberra at the Australian Defence Force Academy, Canberra BC 2610, Australia 2Université de Rennes, ENSCR, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) UMR 6226, F-35000 Rennes, France 3Physique Théorique des Matériaux, CESAM, Université de Liège, B-4000 Sart Tilman, Belgium 4Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales 2234, Australia 5School of Chemistry, The University of Sydney, Sydney, New South Wales 2006, Australia 6Department of Physics, McGill University, Montreal, Québec H3A 2T8, Canada 7Graduate School of Science and Engineering, University of Toyama, Gofuku, Toyama 930-8555, Japan

The magnetic and structural properties of Sc75Fe25 nanoglass prepared by Inert Gas Condensation and compression at 6 GPa are compared with Sc75Fe25 metallic glass produced by melt cooling. Nanoglass consists of nanometer sized glass regions connected by interfacial regions that have a non-crystalline structure. The magnetisation of Sc75Fe25 nanoglass was found to be about an order of magnitude larger than the magnetisation of Sc75Fe25 metallic glass (e.g., similar to 10 A m(2) kg(-1) cf. 0.4 A m(2) kg(-1) at 100 K respectively). The differences in magnetic behaviour of Sc75Fe25 nanoglass and Sc75Fe25 metallic glass result from the exceptional atomic structures of the interfacial regions in nanoglass with ferromagnetic Fe-clusters embedded in a Pauli paramagnetic matrix formed in the nanoglass interfacial regions. This in turn results in a reduction of the magnetic Fe-clusters in nanoglass with increasing external field, B-ex; an effect that has not been observed previously in established magnetic materials. The distributions of Fe and Sc in Sc75Fe25 nanoglass and Sc75Fe25 metallic glass have been determined by scanning transmission electron microscopy; STEM based local radial distribution function (STEM-RDF) and electron energy loss spectroscopy (EELS).

We report detailed investigations on the structural, thermal and magnetic properties of Y2Fe2Si2C over the temperature range 2-300 K using x-ray diffraction, specific heat, Fe-57 Mossbauer spectroscopy and first-principles calculations. Low temperature measurements show no pronounced anomalies which might signal magnetic ordering of the Fe sublattice at low temperature. Analyses of the specific heat data of Y2Fe2Si2C reveal the presence of a localised Einstein mode, suggesting the importance of an optical contribution to the phonon spectrum of Y2Fe2Si2C. Based on electronic structure calculations, we found a low density of states of the Fe 3d bands at the Fermi level. The corresponding density of states are below the Stoner criterion, thus indicating a non-magnetic state of the Fe atoms in Y2Fe2Si2C, in agreement with the experimental findings. (C) 2018 Elsevier B.V. All rights reserved.

The structural and magnetic properties of magnetocaloric Mn(Co1-xNix)Ge compounds have been studied. Two responses to the increase of valence electron concentration on substitution of Ni (3d(8)4s(2)) for Co (3d(7)4s(2)) in the orthorhombic phase (Puma) are proposed: expansion of unit-cell volume and redistribution of valence electrons. We present experimental evidence for electronic redistribution associated with the competition between magnetism and bonding. This competition in turn leads to complex dependences of the reverse martensitic transformation temperature T-M (orthorhombic to hexagonal (P6(3)/mmc)) and the magnetic structures on the Ni concentration. Magnetic transitions from ferromagnetic structures below x = 0.50 to noncollinear spiral antiferromagnetic structures above x = 0.55 at low temperature (e.g., 5 K) are induced by modification of the density of states at the Fermi surface due to the redistribution of valence electrons. T-M is found to decrease initially with increasing Ni content and then increase. Both direct and inverse magnetocaloric effects are observed.

The resistivity of amorphous Fe90Sc10 and Co90Sc10 alloys can be described well in terms of a simple model based on the wave character of electrons and their associated tunnelling over the temperature ranges ~1.9 K to 135 K and ~1.9 K to 12 K respectively. The extended range of agreement between experiment and theory for amorphous Fe90Sc10 is linked with its relatively small mean free path of [Formula: see text]  =  0.32 nm, thus allowing electron waves to tunnel between clusters. On the other hand the restricted region of tunnelling of electron waves for amorphous Co90Sc10 alloys is linked with its relatively large mean free path of [Formula: see text]  =  0.48 nm which restricts the ability for tunnelling between clusters while enabling electron waves to tunnel between different regions with a cluster.