Isothermal Magnetic Entropy Change Research Articles

Structural and magnetic studies on the new Laves phases RE(Co0.667Ga0.333)2 (RE = Gd, Tb, Dy, Ho, and Er). Magnetocaloric effect of Gd(Co0.667Ga0.333)2

Several new MgZn2-type Laves phases with the P63/mmc symmetry and RE(Co0.667Ga0.333)2 stoichiometries (RE=Gd, Tb, Dy, Ho, and Er) were obtained by arc-melting and subsequent annealing. Single crystals with the MgZn2-type structure were extracted from the annealed RE(Co0.667Ga0.333)2 (RE=Gd, Tb, Dy, and Ho) alloys and Ga flux-grown Er(Co0.667Ga0.333)2 sample. Powder and single-crystal X-ray diffraction methods were used for the phase analysis and structural characterization. A decrease in the cell volume due to the lanthanide contraction is observed from Gd(Co0.667Ga0.333)2 to Er(Co0.667Ga0.333)2. RE atoms occupy the 4f site, while Co and Ga are in the 2a and 6h sites. Magnetic behavior of the hexagonal MgZn2-type RE(Co0.667Ga0.333)2 phases strongly depends on the RE. Apparent ferromagnetic transition is observed for RE=Gd, Tb, and Dy, while the other two phases (RE=Ho, and Er) seem to be ferrimagnetic. Magnetocaloric properties of the Gd(Co0.667Ga0.333)2 phase were measured; the small isothermal magnetic entropy change (ΔSiso) value of −4.94J/kgK at 152K and for a ΔH=0–50kOe field change suggests a conventional magnetocaloric effect.

MgZn2-type {Ho, Er, Tm}FeGa rare earth compounds: Crystal structure and magnetic properties

The crystal structure of new hexagonal MgZn2-type {Ho, Tm}FeGa compounds (space group P63/mmc, N 194, hP12) has been established using powder X-ray diffraction studies. The magnetic properties of polycrystalline MgZn2-type ErFeGa compound have been studied using bulk magnetization data. ErFeGa exhibits ferromagnetic ordering at TC = 77K and field sensitive antiferromagnetic-like ordering at Tm ~ 58K in field of 100Oe and Tm ~ 10K in field of 5kOe. The paramagnetic susceptibility follows Curie-Weiss law with effective paramagnetic moment per formula unit (Meff/fu) of 9.59μB and paramagnetic Weiss temperature (ΘP) of 27K.At 2K, ErFeGa exhibits hard magnetic properties with remanent magnetization per formula unit (Mres/fu) of 3.7μB, coercive field (Hcoer) of 8.2kOe and critical field (Hcrit) of ~9.6kOe.The magnetocaloric effect of ErFeGa has been calculated in terms of isothermal magnetic entropy change (ΔSm) and maximum ΔSm values are −5.5J/kgK for a field change of 0–50kOe (relative cooling power RCP50kOe ~ 410J/kg), −13.0J/kgK for a field change of 0–140kOe (RCP140kOe ~ 1230J/kg) at 70K and +1.7J/kgK for a field change of 0–10kOe at 10K (RCP10kOe ~ 34J/kg).

Tuning Magnetocaloric Effect to Near-Room Temperature for MnCo1−x Ge0.5Si0.5 Alloys

The near-room-temperature magnetocaloric materials, i.e., non-stoichiometric MnCo1−xGe0.5Si0.5 (x = 0, 0.025, 0.050, 0.075, and 0.100) alloys with Co atom vacancies, were investigated. The crystal lattice parameters increased as the Co content decreased. The Curie temperatures decreased from high-temperature (393 K) to near-room-temperature (320 K) values as x increased from 0 to 0.100. In an applied magnetic field of 0 to 2 T, the maximum isothermal magnetic entropy change (|ΔSM|) for the MnCo1−xGe0.5Si0.5 alloys was 1.5, 1.7, 2.1, 1.7, and 1.9 J/kg K, while the refrigeration capacity (RC) was 46, 62, 62, 62, and 74 J/kg for x = 0, 0.025, 0.050, 0.075, and 0.100, respectively. Thus, a 27% increase in |ΔSM| and a 60% increase in RC are observed for x = 0.100.

W3CoB3-type {Y, Gd - Ho}3Co4−xAlx (x=0.5−1) rare earth compounds: Specific features of crystal structure and magnetic ordering

The crystal structure of new W3CoB3-type {Y, Gd - Ho}3Co3.25Al0.75, Gd3Co3.5Al0.5 and Tb3Co3Al compounds (Cmcm. N 63, oC28) has been established using powder X-ray diffraction studies. The magnetic properties of Gd3Co3.5Al0.5, Gd3Co3.25Al0.75 and Tb3Co3.25Al0.75 were determined by bulk magnetization measurements and neutron diffraction studies. Gd3Co0.5Al0.5, Gd3Co3.25Al0.75 and Tb3Co3.25Al0.75 exhibit ferrimagnetic ordering below 196K, 161K and 151K, respectively. Tb3Co3.25Al0.75 shows a spin-reorientation transition at ~42K. Below the ferrimagnetic ordering temperature Gd3Co3.25Al0.75 and Tb3Co3.25Al0.75 are soft ferrimagnets, meanwhile Tb3Co3.25Al0.75 shows magnetic hardness below the spin-reorientation transition with remanent magnetization per formula unit of 9.7 μB and coercive field of 15kOe at 2K.The magnetocaloric effects of Gd3Co3.25Al0.75 and Tb3Co3.25Al0.75 were calculated in terms of isothermal magnetic entropy change and they reach maximum values of −4.9J/kg·K at 135–145K and −3.7J/kg·K at 115–135K, respectively, for a field change of 0–50kOe. Low temperature magnetic ordering in Tb3Co3.25Al0.75 is accompanied by a positive magnetocaloric effect with isothermal magnetic entropy changes of +13.6J/kg·K at 10K for a field change of 0–50kOe and +0.9J/kgK at 45K for a field change of 0–10kOe.Neutron diffraction study in zero applied field shows mixed ferro-antiferromagnetic ordering of Tb3Co3.25Al0.75 with a wave vector K0=[0, 0, 0]. Below ~ 137K Tb3Co3.25Al0.75 exhibits non-collinear ferrimagnetic ordering of terbium and cobalt sublattices with resulting of b-axis ferromagnetic and c-axis antiferromagnetic components of Cmc′m={1, mx}×{1, mz/[0, 0, 1/2]}×{1, i′}×{1, 1/[1/2, 1/2, 0]} magnetic space group. The spin-reorientation transition in Tb3Co3.25Al0.75 below ~38K corresponds to appearance of additional a-axis ferromagnetic component and decreasing of symmetry of magnetic ordering down to C2′/c={1, mz/[0, 0, 1/2]}×{1, i′}×{1, 1/[1/2, 1/2, 0]} magnetic space group.

Improving the refrigeration capacity of Gd-rich wires through Fe-doping

Abstract Herein, the magnetocaloric effect (MCE) of Fe-doped Gd-rich microwires has been investigated. Experimental results indicated that this type of the microwires has entirely amorphous microstructure and smooth surface, and exhibits a relatively higher Curie temperature (∼121.8 K) as for the appropriate Fe substitution, and a remarkable and reversible MCE effect with almost no thermal or magnetic hysteresis loss. For a magnetic field change of 5 T, the isothermal magnetic entropy change (-Δ S m ) for the longitudinal direction reaches as large as 10.33 J kg −1 K −1 , besides the refrigerant capacity (RC) achieves a relatively large value of 748.22 J kg −1 . Meanwhile, the Arrott plots also indicate that the ferromagnetic-paramagnetic transition is of the second-order. Therefore, it can be concluded that the obtained Fe-doped Gd-rich wires are used as intelligent materials with enhanced MCE property for potential multifunctional applications in magnetic refrigeration field.

Exploiting Magnetism and Magnetocaloric Effect in Nd0.55Sr0.45Mn0.98Ga0.02 O 3

We report results of the magnetization and magnetocaloric effect in lightly Ga-doped perovskite manganites Nd0.55Sr0.45Mn0.98Ga0.02O3. It undergoes a second-order paramagnetic to ferromagnetic transition at TC = 250 K and shows a strong ferromagnetic properties below TC. However, an obvious upward deviation from the Curie-Weiss law far above TC indicates the existence of non-Griffiths-like behavior in paramagnetic phase. Together with the measurements of isothermal magnetization around the Curie temperature, the unsaturated magnetization curves under high magnetic field of 7.0 T imply that the Ga-substitution causes the formation of antiferromagnetic phase due to some localized charge order phases generated in this composition. Based on the data of isothermal magnetization measured around TC and Maxwell relation, we have calculated the maximum isothermal magnetic entropy change of 6.23 J/kg K for Δμ0H = 7.0 T magnetic field variation. Though only a moderate magnetic entropy change were obtained, a considerable large relative cooling power of 260 J/kg for Δμ0H = 7.0 T and 182 J/kg for Δμ0H = 5.0 T were found in this sample, this ensure it to be a potential candidate material to be applied in the magnetic refrigeration.

Effect of rapid quenching on the magnetism and magnetocaloric effect of equiatomic rare earth intermetallic compounds RNi (R = Gd, Tb and Ho)

Magnetocaloric effect (MCE) in RNi (where R=Gd, Tb and Ho) compounds has been studied in their arc-melted and melt-spun forms. The compound GdNi has the orthorhombic CrB-type structure (Space group Cmcm, No. 63) and the compound HoNi has the orthorhombic FeB-type structure (Space group Pnma, No. 62) at room temperature regardless of their synthesis condition. However, arc-melted TbNi orders in a monoclinic structure (Space group P21/m, No. 11) and when it is rapidly quenched to a melt-spun form, it crystallizes in an orthorhombic structure (Space group Pnma, No. 62). The arc-melted GdNi, TbNi and HoNi compounds order ferromagnetically at ∼69K, ∼67K and ∼36K (TC) respectively. While the melt-spun GdNi shows about 6K increase in TC, the ordering temperature of TbNi remains nearly the same in both arc-melted and melt-spun forms. In contrast, a reduction in TC by about 8K is observed in melt-spun HoNi, when compared to its arc-melted counterpart. Isothermal magnetic entropy change, ∆Sm, calculated from the field dependent magnetization data indicates an enhanced relative cooling power (RCP) for melt-spun GdNi for field changes of 20kOe and 50kOe. A lowered RCP value is observed in melt-spun TbNi and HoNi. These changes could have resulted from the competing shape anisotropy and the granular microstructure induced by the melt-spinning process. Tailoring the MCE of rare earth intermetallic compounds by suitably controlled synthesis techniques is certainly one of the directions to go forward in the search of giant magnetocaloric materials.

The Calculated Magnetic Properties and Magneto-caloric Effect in Compound MnAs

The aim of this study is to investigate and determine the magnetic properties and the magneto-caloric effect of the system MnAs with the spin moment (S = 2). To attain this aim, we first use Ab initio method to determine the density of the state and exchange couplings of the compound. This stage is followed by analysis and discussion of ground-phase diagrams, and then by examination of all stable phases. To investigate further the compound, we establish the magnetic properties and the magneto-caloric effect of the compound in question by Monte Carlo simulation method in the framework of the Ising model, and consequently, we achieve a number of results such as the determination of the magnetization, the susceptibility, the specific heat and the Binder’s fourth-order cumulate of the order parameter, the plotting of the effect of the exchange coupling and temperature on the hysteresis loop behaviors, the calculation of the Binder’s fourth-order cumulate of energy, and finally the isothermal magnetic entropy change, adiabatic temperature change and relative cooling power (RCP) for the different external magnetic fields.

Magnetocaloric properties of R2NiMnO6 (R=Pr, Nd, Tb, Ho and Y) double perovskite family

Double perovskite R2NiMnO6 (R=Pr, Nd, Tb, Ho and Y) composites are prepared via solid state synthesis or nitrate route. Isothermal magnetic entropy change (ΔSM(T,H)) and relative cooling power (RCP) for all systems are calculated and compared. All of them possess relatively high values of ΔSM(T,H) and RCP as compared to many perovskite and double perovskite systems reported previously. Ho2NiMnO6 has the highest value for |ΔSM(T,H)| and RCP as 8.4JKg−1K−1 at 70kOe and 59.18JKg−1 at 20kOe respectively. This study highlights the potential of magnetocaloric refrigerant materials at low temperature.

Table-like magnetocaloric effect involving the enhancement of refrigerant capacity in (AMn0.9Ti0.1O3)1−x/(AMn0.85Ti0.15O3)x composite

ABSTRACTIn this paper, a table-like magnetocaloric effect (MCE) is obtained in the (AMn0.9Ti0.1O3)1−x/(AMn0.85Ti0.15O3)x composite system. A flattening behaviour of the entropy change is investigated from the isothermal magnetic entropy change versus temperature curves ∆S(T) of AMn0.9Ti0.1O3 and AMn0.85Ti0.15O3 (A = La0.57Nd0.1Pb0.33) manganite materials. Both compounds exhibit nearly some large MCE, 5.2–4.85 J kg−1 K−1, under an applied field of 0–5 T, around their respective Curie temperature (TC) ranged from 279 to 299 K. The temperature dependence of the isothermal magnetic entropy change ΔS(T) is calculated for (AMn0.9Ti0.1O3)1−x/(AMn0.85Ti0.15O3)x composite with 0 ≤ x ≤ 1. The optimum ΔS(T) of the composite with x = 0.495 approaches a nearly constant value of ∼3.63 J kg−1 K−1 in a field change of 0–5 T in a wide temperature span over 15 K, resulting in large refrigerant capacity value of ∼172.3 J kg−1. The (AMn0.9Ti0.1O3)0.505/(AMn0.85Ti0.15O3)0.495 composite system indicates that this approach can be used to design magnetic refrigerant materials with enhanced magnetocaloric response in a magnetic refrigerator performing an Ericsson cycle near room temperature.

Microstructure, magnetic and magnetocaloric properties of Fe2–x Mn x P0.4Si0.6 alloys

The present work is devoted to investigating the microstructure, magnetism and magnetocaloric effects of Si- and Mn-rich FeMn(P,Si) alloys. The Mn-substituted alloys with Fe2– x Mn x P0.4Si0.6 ( x = 1.25, 1.30, 1.35, 1.40, 1.45 and 1.50) were prepared by high-energy ball milling and solid-state reaction. Experimental results show that the alloys crystallized into a majority Fe2P-type hexagonal structure, coexisting with minor amounts of (Mn,Fe)3Si and (Mn,Fe)5Si3 phases. The Curie temperature decreased linearly from 321 to 266 K with increasing Mn content from 1.25 to 1.50 in Fe2– x Mn x P0.4Si0.6 alloys. The first-order magnetic phase transition became weakened and the second-order magnetic phase transition became dominated with increasing Mn content. Fe0.75Mn1.25P0.4Si0.6 alloy presents a maximum isothermal magnetic-entropy changes of 7.2 J (kg K)–1 in a magnetic field change of 0–1.5 T. The direct measurement shows that Fe0.7Mn1.3P0.4Si0.6 and Fe0.65Mn1.35P0.4Si0.6 alloys exhibit a maximum adiabatic temperature change of 1.8 K in a magnetic field change of 0–1.48 T. The thermal hysteresis for all alloys is less than 4 K. These experimental results reveal that Fe2– x Mn x P0.4Si0.6 alloys could be a candidate material for magnetic refrigeration.

Solvent-free mechanochemical synthesis and magnetic properties of rare-earth based metal-organic frameworks

Mechanical milling of benzene 1,3,5-tricarboxylic acid [C6H3(COOH)3], both with the single and mixed rare earth carbonates [R2(CO3)3·xH2O; R = Gd, Tb and Dy], leads to the formation of metal-organic frameworks [R{C6H3(COO)3}] that adopt MIL-78 type structure. M(T) data of the investigated MOFs do not show any apparent onset of long range magnetic ordering down to 2 K. The M(H) data for Gd{C6H3(COO)3}collected at 2 K show deviations from the magnetization behavior expected for non-interacting Gd3+ ions. For the Gd based MOF the temperature dependence of the isothermal magnetic entropy change (i.e. magnetocaloric effect, ΔSM) exhibits a monotonous increase with decreasing temperature and at T = 3.5 K it reaches 34.1 J kg−1K−1 for a field change (ΔH) of 50 kOe. For the same ΔH the maximum values of ΔSM for R = Tb and Dy are 5.5 J kg−1K−1 and 8.5 J kg−1K−1 at 9.5 K and 4.5 K, respectively.

The thermomechanical stability of Fe-based amorphous ribbons exhibiting magnetocaloric effect

The Fe–Nb–B and Fe71.5Cr2Si13.5B9Nb3Cu1 alloys have been prepared by rapid quenching from the melt, and the magnetic properties of alloys in the vicinity of the magnetic ordering have been studied before and after thermomechanical processing. It has been shown that change in the Fe:Nb:B ratio allows tuning the magnetic ordering temperature and the position of maximum of the isothermal magnetic entropy change \( \left| { - \Delta S_{m} } \right| \) from 256 to 333 K. The thermomechanical treatment of alloys at 623 K under applied tensile stresses observed does not affect remarkably the magnetocaloric properties of alloys. The combination of high thermomechanical stability, good electrical, anti-corrosive and thermomagnetic properties makes these alloys promising for use in magnetic refrigeration devices.

Searching the conditions for a table-like shape of the magnetic entropy in the magnetocaloric LBMO2.98/LBMO2.95 composite

The conditions to obtain a table-like behavior of the entropy change, on the composite system $(LBMO_{2.98})_{1-x}/(LBMO_{2.95})_{x}$ , have been investigated from the isothermal magnetic entropy change versus temperature curves $ \Delta S(T)$ of La2/3Ba1/3MnO2.98 and La2/3Ba1/3MnO2.95 materials. The latters are characterized by Curie temperatures ( $ T_{C}$ ) values (310 K for La2/3Ba1/3MnO2.98 and 292 K for La2/3Ba1/3MnO2.95 around room temperature. The temperature dependence of the isothermal magnetic entropy change $\Delta S(T)$ has been calculated for the composite system with $ 0 \le x \le 1$ . The optimum magnetocaloric effect (MCE) properties, i.e., a $\Delta S(T)$ curve with table-like shape, have been found in the temperature interval of 293-309 K for the composite with $ x = 0.48$ at 1 T. The $\Delta S(T)$ of the composite comes close to a constant value of 1.73(7)J/(kg ·K). A large refrigerant capacity value of $\sim 66.4(9)$ J/kg is obtained in a wide temperature span over 16 K. This composite can be used as the working material in the Ericsson-cycle magnetic regenerative refrigerator. These results make the $(LBMO_{2.98})_{0.52}/(LBMO_{2.95})_{0.48}$ system a promising material for practical magnetic refrigeration using a lower field (1 T), which is much easier to generate by permanent magnets, than higher fields, like 2 T.

CeNi3-type rare earth compounds: crystal structure of R3Co7Al2 (R=Y, Gd–Tm) and magnetic properties of {Gd–Er}3Co7Al2, {Tb, Dy}3Ni8Si and Dy3Co7.68Si1.32

The crystal structure of new CeNi3-type {Y, Gd–Tm}3Co7Al2 (P63/mmc. N 194, hP24) compounds has been established using powder X-ray diffraction studies. The magnetism of Tb3Ni8Si and Dy3Ni8Si is dominated by rare earth sublattice and the magnetic properties of R3Co7Al2 (R =Gd–Er) and Dy3Co7.68Si1.32 are determined by both rare earth and cobalt sublattices. Magnetization data indicate ferromagnetic ordering of {Tb, Dy}3Ni8Si at 32K and 21K, respectively. Gd3Co7Al2 and Tb3Co7Al2 exhibit ferromagnetic ordering at 309K and 209K, respectively, whereas Dy3Co7Al2, Ho3Co7Al2, Er3Co7Al2 and Dy3Co7.68Si1.32 show a field dependent ferromagnetic-like ordering at 166K, 124K, 84K and 226K, respectively followed by a low temperature transition at 34K for Dy3Co7Al2, 18K for Ho3Co7Al2, 56K for Er3Co7Al2, 155K and 42K for Dy3Co7.68Si1.32. Among these compounds, Dy3Ni8Si shows largest magnetocaloric effect (isothermal magnetic entropy change) of −11.6J/kg·K at 18K in field change of 50kOe, whereas Tb3Co7Al2, Dy3Co7Al2 and Dy3Co7.68Si1.32 exhibit best permanent magnet properties in the temperature range of 2–5K with remanent magnetization of 11.95 μB/fu, 12.86 μB/fu and 14.4 μB/fu, respectively and coercive field of 3.0kOe, 1.9kOe and 4.4kOe, respectively.

Impact of Ba Substitution on the Magnetocaloric Effect in La1-xBaxMnO3 Manganites

La1-xBaxMnO3 (x = 0.30, 0.35 and 0.40) samples have been prepared by solid-state reaction method. The X-ray diffraction (XRD) study showed that all the samples crystallized in a rhombohedral structure with an R-3c space group. Variation of the magnetization as a function of the temperature and applied magnetic field was carried out. All the samples revealed ferromagnetic to paramagnetic (FM-PM) phase transition at the Curie temperature TC ~ 342 K. The magnetic entropy change was also studied through examination of the measured magnetic isotherms M(H, T) near TC. The magnetocaloric effect was calculated in terms of the isothermal magnetic entropy change. The maximum entropy change reaches a value of 1.192 J/ kgK under a magnetic field change of 2.5T for the La0.6Ba0.4MnO3 composition. The relative cooling power (RCP) is 79.31 J/ kg for the same applied magnetic field.

Magnetic ordering of Hf3Ni2Si3-type {Sm, Tb, Er}3Co2Ge3 and {Tb, Ho}3Ni2Ge3 compounds

The magnetic ordering of Hf3Ni2Si3-type {Sm, Tb, Er}3Co2Ge3 and {Tb, Ho}3Ni2Ge3 compounds (space group Cmcm, oC32) was investigated via magnetization measurements and neutron diffraction study in a zero-applied field. {Sm, Tb, Er}3Co2Ge3 and Ho3Ni2Ge3 exhibit field sensitive complex antiferromagnetic orderings with TN=51K, Tm=10K for Sm3Co2Ge3, TN=34K, Tm=13K for Tb3Co2Ge3, TN=7K for Er3Co2Ge3 and TN=11K for Ho3Ni2Ge3. At 2K and above the critical field of ~5kOe, 20kOe, 4kOe and 7kOe for Sm3Co2Ge3, Tb3Co2Ge3, Er3Co2Ge3 and Ho3Ni2Ge3, respectively, saturation magnetizations per rare-earth atom are 6.5μB for Tb3Co2Ge3, 7.0μB for Er3Co2Ge3 and 8.0μB for Ho3Ni2Ge3 in the field of 140kOe, whereas magnetization of Sm3Co2Ge3 has an antiferromagnetic behaviour. The isothermal magnetic entropy change, ΔSm, indicates a field-induced ferromagnetic ordering in Sm3Co2Ge3, Tb3Co2Ge3, Er3Co2Ge3 and Ho3Ni2Ge3 with a maximal ΔSm value of −10.9J/kgK for Ho3Ni2Ge3 at 11K for a field change of 50kOe.In a zero-applied magnetic field, below TN=33K and down to TmND=15K Tb3Ni2Ge3 shows an ac-antiferromagnetic ordering with the C2′/c magnetic space group, a K0=[0, 0, 0] propagation vector and a aTb3Ni2Ge3×bTb3Ni2Ge3×cTb3Ni2Ge3 magnetic unit cell. Below TmND=15K, its magnetic structure is a sum of the ac-antiferromagnetic component with the C2′/c magnetic space group of the K0 vector and a sine-modulated a-antiferromagnetic component of the K1=[0, 0, ±1/3] propagation vector (the magnetic unit cell is aTb3Ni2Ge3×bTb3Ni2Ge3×3cTb3Ni2Ge3). The magnetic structure is made from the ‘Tb2 - 2Tb1′ clusters of the Tb1 8f and Tb2 4c sublattices with a dominant role of the Tb2 sublattices in the magnetic ordering of Tb3Ni2Ge3.

Influence of crystallite size reduction on the magnetic and magnetocaloric properties of La0.6Sr0.35Ca0.05CoO3 nanoparticles

In this paper, three samples of La0.6Sr0.35Ca0.05CoO3 with different crystallite sizes were prepared by a combination of the sol–gel and mechanical milling methods, with milling times tm of 0 (M0), 1h (M1) and 2h (M2). From the XRD and SEM analyses, it is confirmed that the grain size decreases with increased milling time. The value of the grain size observed from SEM is much larger than that observed from XRD analysis, which indicates that each particle observed by SEM consists of several crystallized grains. The reduction of the crystallite size (D) decreased the Curie temperature (TC) and magnetization values, and broadened the phase-transition region of the materials. The magnetocaloric effect was calculated in terms of the isothermal magnetic entropy change. The maximum value of the magnetic entropy change of the M0 sample, obtained from the M(μ0H) plot data, is |ΔSMmax|=1.35J/kgK for an applied magnetic field of 5T. In addition, the μ0H/M versusM2 curves at temperatures around TC prove that the samples exhibit a second-order magnetic phase transition. The universal behavior obtained from the ΔSM variation curves confirmed the second-order transition for all the samples.

Improving mechanical and magnetocaloric responses of amorphous melt-extracted Gd-based microwires via nanocrystallization

We report on the structural, mechanical, and magnetocaloric properties of annealed melt-extracted Gd53Al24Co20Zr3 amorphous microwires of ∼70 μm diameter. During heat treatment small islands of nanocrystallities are generated and isolated in the amorphous region for the wires. The size of the nanocrystallities ranges from 5 nm to 10 nm. The observed lattice distortion from the nanocrystallities causes changes in the magnetic properties of the wires. The annealing temperature of 100 °C has the largest strength (1845 MPa) as compared to wires annealed at other temperatures. This is likely to trigger nanophase transformation in the amorphous region and these nanocrystals have been preserved through the increase of annealing temperature. The formulation of the nanocrystalline islands is also verified by the selected-area electron diffraction (SAED). The microwires exhibit a large and reversible magnetocaloric effect (MCE), with the maximum isothermal magnetic entropy change (−ΔSM) and refrigerant capacity (RC) values of 9.5 J/kg K and 689 J/kg respectively for the microwire annealed at 100 °C. This RC is about 35%, 67%, and 91% larger than those of bulk Gd53Al24Co20Zr3 (∼509 J/kg), Gd (∼410 J/kg), and Gd5Si2Ge1.9Fe0.1 (∼360 J/kg) regardless of their ordering temperatures. These results demonstrate the ability to tune the mechanical and magnetic properties of the microwires by thermal annealing.

Structural, Magnetic, and Magnetocaloric Studies of Ni50Mn30Sn20 Shape Memory Alloy

We have synthesized a nominal composition of Ni50Mn30Sn20 alloy using arc melting technique. Rietveld refinement confirms the austenite L21 structure in Fm-3m space group. Electrical resistivity has been found to clearly exhibiting two different phenomena viz. a magnetic transition from paramagnetic to ferromagnetic and a structural transition from austenite to martensitic phase. Thermo-magnetization measurements M(T) confirms ferromagnetic transition temperature TC at 222 K and martensitic transition starting at 127 K(MS). Magnetization measurement M(H) at 10 K confirms the ferromagnetic state. Frequency dependence of ac susceptibility \c{hi}' at low temperature suggests spin glass behavior in the system. The isothermal magnetic entropy change values have been found to be 1.14 J/Kg.K, 2.69 J/Kg.K and 3.9 J/Kg.K, with refrigeration capacities of 19.6 J/kg, 37.8 J/kg and 54.6 J/kg for the field change of 1, 2 and 3 Tesla respectively at 227 K.