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.

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 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.

A simple synthesis route for the Nd2Fe14C compound with good permanent magnetic properties is presented. Being high-energy ball-milled in heptane (C7H16) for 8 h, the NdFe3.5 alloy consisting of Nd2Fe17 and Nd phases disproportionates into NdH2+delta d and alpha-Fe. Subsequently, NdH2+delta decomposes when annealed from room temperature to 900 degrees C under vacuum, and H-2 is released. Meanwhile Nd2Fe14C, NdC and little alpha-Fe phases are formed in the final product. H and C atoms come from the decomposition of heptane. Coercivity of 1.39 T and maximum magnetic energy product of 62.7 kJ m(-3) have been achieved. Too short a ball-milling time results in the insufficient disproportionation of NdFe3.5 alloy and the residue of Nd2Fe17 phase in the final product. Too long a ball-milling time results in the appearance of NdC2 and more alpha-Fe phases besides Nd2Fe14C and NdC phases. Hexane (C6H14), octane (C8H18) and nonane (C9H20) have been proved to have a similar effect to heptane.

A traditional hydrogenation disproportionation desorption recombination (HDDR) technique succeeds in fabricating bonded Nd–Fe–B magnet while encounters difficulty in the fabrication of Sm–Co magnet, due to the higher thermodynamic stability of the Sm–Co compounds against the disproportionation by hydrogen. To induce the disproporationation of Sm–Co compounds, high pressure hydrogen under high temperature has to be employed. This paper reports a hydrogenation and disproporationation reactions of SmCo5 compound that does not involve gaseous hydrogen: high energy ball milling in heptane. The H atom comes from heptane. Being milled for more than 600min, the SmCo5 phase completely disproportionates into Sm hydride (SmH2±δ) and cubic Co. Heating the disproportionated powder in vacuum from room temperature to 800°C, two desorption processes, one between 200 and 400°C and the other around about 600°C, were observed. The desorbed gas is proved to be hydrogen by gas chromatography. The Heated product consists of mainly hexagonal SmCo7 phase with a TbCu7 structure. The coercivity of SmCo7 phase is larger than 1T, being able to meet the demand of permanent magnetic application. Excess high energy ball milling results in the appearance of minor SmCoC2 and cubic Co phases.

CeCo5 permanent magnetic alloy has been processed by surfactant assisted high energy ball milling. Heptane and oleic acid were used as the solvent and surfactant, respectively. The amount of surfactant used was 50% by weight of the starting powder. The produced particles were deposited on a piece of copper (4mm in length and width) under a magnetic field of 27kOe applied along the copper surface and immobilized by ethyl α-cyanoacrylate. Scanning electron microscope pictures show that the particles are flakes, several μm in length and width and tens of nm in thickness. X-ray diffraction patterns and magnetic measurements prove that the flakes are crystalline with c-axes magnetic anisotropy. The easy magnetization axis is oriented perpendicular to the surface of the flake. A maximum coercivity of 3.3kOe was obtained for the sample milled for 40min.

CeCo5.4 ribbons have been prepared by melt spinning at wheel speeds v=5, 15, 25 and 35 m/s. The ribbons are essentially single 1:5 phase, and have significant crystallographic texture and magnetic anisotropy. The ribbon's longitudinal direction is easy direction, and normal to the ribbon plane direction is hard direction. For v=5 m/s [1 1 1]-axes of the grains near non-contact surface of the ribbon are normal to the ribbon plane. With increase of v, [1 1 0] and [2 0 0]-axes of the grains near non-contact surface rotate toward the normal direction and the c-axes parallel to the ribbon plane. The anisotropy increases up to v=25 m/s and then decreases. The grains near contact-wheel surface are randomly oriented for all v. The coercivity increases with increase of v due to decrease of the grain size. The values of coercivity are smaller in the easy direction and are larger in the hard direction, meaning that the coercivity mechanism is mainly characterized by domain wall pinning.

A mixture of tetrachloride (ZrCl4) and lithium nitride (Li3N) powders was milled in a high-energy ball mill under Ar ambient. Mechanochemical reaction of ZrCl4 and Li3N occurred during the milling process and produced LiCl and ZrN with rocksalt structure. It was found by in situ measurement of surface temperature of the vial in milling process that the reaction began as milling time reached about 7min and finished in a few of seconds, accompanied by release of a great deal of heat. This result implies that the reaction is a self-propagating one, and that ZrN powders can be fabricated by milling in very short time. By chemical separation of the products, high pure ZrN powders with nanometer scale were obtained. The present work provides a technique for synthesis of high pure ZrN nanopowders with short time, large mass and low cost. The thermodynamic and kinetic mechanisms of formation of the ZrN are discussed in detail.

The magnetization curves along the crystal axes for Gd2Fe17 and Gd2Fe17H3 were analysed based on the single-ion model. If the Gd-Fe exchange interaction has been taken as isotropic as usual, the fitted values of magneto-crystalline anisotropy of the Fe sublattices in Gd2Fe17 and Gd2Fe17H3 would become unreasonably different from those of the corresponding Y or Lu compounds. It was shown that the large difference is caused by the neglect of the anisotropy of the Gd-Fe exchange interaction.