ΔSM Values Research Articles

Magnetic, magnetocaloric and critical exponent properties of amorphous [formula omitted] ribbons prepared by melt-spinning technique

Amorphous Fe67Y33 ribbons were prepared using melt-spinning method and their magnetic, magnetocaloric and critical exponent properties were investigated. The magnetocaloric behavior and the magnetic transition were analyzed in terms of Landau theory around the transition temperature. Good agreement was found between the magnetic entropy (-ΔSM) values estimated by Landau theory and those obtained using classical Maxwell relation. The magnetic transition nature is of a second order from ferromagnetic to paramagnetic states with a Curie temperature of 240 K. Through various techniques such as modified Arrott plots (MAP), Kouvel–Fisher (KF), critical isotherm analysis (CIA) and Windom scaling relation (WSR); the critical exponents (β, γ and δ) were found to be close to those of the long-range mean-field approach. In addition, an autonomous analysis of the critical behavior is presented in terms of the magnetocaloric effect confirming the validity of the mean-field approach.

Impact of small Er rare earth element substitution on magnetocaloric properties of (La0.9Er0.1)0.67Pb0.33MnO3 perovskite

In this work, the effect of Er substitution on the magnetic and magnetocaloric properties has been studied for (La0.9Er0.1)0.67Pb0.33MnO3 perovskite synthesized by the sol-gel procedure. Magnetization measurements performed as a function of both temperature and magnetic field in order to determine magnetic and magnetocaloric properties. The temperature dependence of magnetization measured under 5 mT magnetic field indicate that sample exhibits ferromagnetic (FM) to paramagnetic (PM) transition with increasing temperature. The Curie temperature (TC) decreases with Er-doping from 358 K for La0.67Pb0.33MnO3 to 349 K. From the isothermal magnetization measurements taken up to 5T around the TC in 3 K intervals, the magnetic entropy change (ΔSM) values of the sample have been determined for different magnetic fields. The ΔSMmax value has been calculated as 0.98, 1.73, 2.33, 2.85 and 3.23 Jkg−1K−1 for 1, 2, 3, 4 and 4.8 T, respectively. The type of magnetic phase transition has been determined as the second order from the slope of Arrott plots.

Magnetocaloric Effect of Micro- and Nanoparticles of Gd5Si4

Materials exhibiting a large magnetocaloric effect (MCE) at or near room temperature are critical for solid-state refrigeration applications. The MCE is described by a change in entropy (ΔSM) and/or temperature (ΔTad) of a material in response to a change in applied magnetic field. Ball milled materials generally exhibit smaller ΔSM values compared to bulk; however, milling broadens the effect, potentially increasing the relative cooling power (RCP). The as-cast Gd5Si4 is an attractive option due to its magnetic transition at 340 K and associated MCE. Investigation of effect of particles size and transition temperature in the binary material, Gd5Si4, can lead to development of functionally graded bulk material with higher MCE and RCP than the traditional bulk materials. A two-step ball-milling process, in which coarse powder of Gd5Si4 was first milled with poly(ethylene glycol) followed by milling in heptane was used to produce fine particles of Gd5Si4 that showed a broad distribution in particle size. Magnetic measurement on the milled sample obtained after washing with water show a decrease in Curie temperature and significant broadening of the magnetic transition. Compared to bulk Gd5Si4, the maximum MCE of the milled samples is also reduced and shifted down by close to 30 K, but the MCE remains substantial over a broader temperature range. The RCP of both milled samples increased 75% from the bulk material.

Enhanced magnetocaloric effect in terbium-doped gadolinium oxide nanoparticles

A simple, solvothermal method has been used to synthesize gadolinium oxide nanoparticles with 3 wt% terbium doping (3% Tb-doped Gd2O3). The particles have cubic crystal structure (Space group Ia-3, No. 206). The mean particle size estimated from transmission electron microscopy is ∼55 nm and the crystallite size estimated from powder X-ray diffraction data is ∼28 nm. The sample, 3% Tb-doped Gd2O3, remains paramagnetic from 300 K down to 5 K. Magnetocaloric effect (MCE) is estimated in terms of isothermal magnetic entropy change (ΔSm) at low temperatures. The maximum value of ΔSm at 6 K for 70 kOe field change is found to be about −20.9 Jkg−1K−1. This value is quite large and is comparable with that of pristine nanosized Gd2O3. Therefore rare earth-doped Gd2O3 nanostructures could also be useful in low temperature magnetic refrigeration.

Magnetocaloric effect of Gd2O3 nanorods with 5% Eu-substitution

Abstract One dimensional Gd2O3 nanorods with 5% Eu substitution at Gd-site have been synthesized by a simple, inexpensive, hydrothermal process without using any catalyst or template. Structural, spectroscopic, magnetic and magnetocaloric properties of these nanorods are studied. Powder X-ray diffraction data confirm that these samples have cubic structure (Space group Ia-3) at 300 K. High resolution transmission electron microscopy images suggest the average diameter of nanorods to be ~14 nm. However, the rod length is found to vary from about 50 nm to 140 nm. Raman spectrum shows a peak at ~363 cm−1 as expected for the cubic phase of Gd2O3. The 5% Eu substituted Gd2O3 sample remains paramagnetic from 300 K down to 5 K. Using magnetization–field data obtained at various temperatures, isothermal magnetic entropy change (ΔSm) is calculated. The maximum ΔSm value at 6 K for 70 kOe field change is about −30.3 Jkg−1 K−1. This value is quite large compared to that of the pure Gd2O3 nanotube samples. Thus nanostructured Gd2O3 with small rare-earth substitution at Gd-site exhibit appreciable magnetocaloric effect and these nanomaterials may be suitable for low temperature magnetic refrigeration applications.

Trinuclear and Mononuclear Lanthanoid Complexes Containing 2‐Methyl‐8‐quinolinolate: Synthesis, Structures, and Magnetic Properties

Two series of new lanthanoid complexes containing 2‐methyl‐8‐quinolinolate (MQ–) have been prepared at elevated temperatures. Lighter elements yield trinuclear complexes [Ln3(MQ)9(HMQ)]·5H2O·3MeOH (1Ln, where Ln = Pr, Eu, Gd, Tb, Dy and Ho) by solvothermal reactions, and heavier lanthanoids yield the mononuclear complexes [Ln(MQ)3(HMQ)]·HMQ·MeOH (2Ln, where Ln = Dy, Ho, Er and Yb), with overlap between the two series found in the cases of Dy and Ho. Magnetic studies reveal that 1Tb, 1Dy, and 2Er show distinct slow magnetic relaxation under external DC fields. The magnetic data for 1Gd yielded the J value for weak antiferromagnetic coupling and the magnetocaloric –ΔSm value of 20 J kg–1 K–1 at 2 K and ΔH = 5 T.

Two linear-shaped Gd4 clusters based on a multidentate ligand: Synthesis, structures, and magnetic refrigeration

Two novel and tetranuclear gadolinium clusters, namely, [Gd4(L)2(dbm)6(CH3OH)2] (1) and [Gd4(L)2(dbm)6(C2H5OH)2] (2) (H3L = (6-Hydroxymethyl)-N′-((2,3-dihydroxyphenyl)-methylene)picolinohydrazide and dbm = dibenzoylmethane), were assembled by the reaction of a multidentate ligand H3L with Gd(dbm)3·2H2O in different solvent system. Both the two Gd4 clusters have an approximate linear-shaped arrangement and the four central Gd3+ ions are connected by six μ2-O atoms. Direct-current (dc) magnetic susceptibility measurements of clusters 1 and 2 indicated that the weak antiferromagnetic interactions between adjacent Gd3+ ions both exist in clusters 1 and 2. It's particularly significant that clusters 1 and 2 display significant cryogenic magnetocaloric effects with maximum −ΔSm values of 21.39 and 20.26 J kg−1 K−1 at 2.0 K and 7.0 T, respectively.

Structure, magnetocaloric properties and thermodynamic modeling of enthalpies of formation of (Mn,X)-Co-Ge (X = Zr, Pd) alloys

Enthalpies of formation of (Mn,X)-Co-Ge (X = Zr, Pd) system in different structural states were analyzed utilizing the semi-empirical Miedema's model combined with the geometric one. Substitution of Mn by Zr significantly improves glass forming ability of Mn-Co-Ge, with parent equiatomic alloy among them. Chosen half-Heusler alloys, which are thermodynamically stable for the mentioned elemental compositions, were obtained by arc-melting. The x-ray diffraction studies confirmed coexistence of orthorhombic NiTiSi-type and hexagonal Ni2In-type structures for parent MnCoGe alloy and (Zr, Pd)-substituted samples. Thermomagnetic curves and magnetic isotherms allowed to reveal the Curie temperature TC and a magnetic entropy change ΔSM and allowed to analyze the influence of both substitutive elements. The Curie temperatures are equal to 293 K for MnCoGe, 278 K for Mn0.9Zr0.1CoGe alloy and 318 K for Mn0.9Pd0.1CoGe. The maximum magnetic entropy change ΔSM values, calculated for the change of external magnetic field of about 5 T, amount to 6.17, 2.94, and 11.11 J (kg K)−1 for MnCoGe, Mn0.9Zr0.1CoGe and Mn0.9Pd0.1CoGe, respectively. Differences in magnetic characteristics of the analyzed alloys are mainly caused by the changes of extent of undergoing first order magnetostructural transition with Pd and Zr atoms substitution. The presence of Pd d moments is also beneficial for the enhancement of total magnetic moment and maximum value of magnetic entropy changes in Mn0.9Pd0.1CoGe alloy.

Simultaneous magnetic and structural transitions in Nd0.15Ca0.85MnO3 manganite: Magnetization and neutron diffraction studies

The manganite Nd0.15Ca0.85MnO3 crystallizes in GdFeO3-type, orthorhombic structure (space group Pnma) at 300 K and orders antiferromagnetically at 112 K (TN). Magnetization-field (M-H) isotherms indicate metamagnetic transition at temperatures below TN. However, metamagnetism does not lead to saturation in magnetization. The magnetization value at 2 K in 140 kOe field is only 0.4 μB/f.u. The isothermal magnetic entropy change (ΔSm) has been calculated using the M-H data and inverse magnetocaloric effect is observed around TN and the maximum value of ΔSm is ∼12.2 J kg−1K−1 at 107.5 K for 140 kOe field change. Powder neutron diffraction study in zero applied field reveals monoclinic distortion of Nd0.15Ca0.85MnO3 crystal lattice and antiferromagnetic ordering of Mn sublattice in ac-plane with wave vector K = [1/2, 0, 1/2] at 125 K. From the neutron data, the Mn magnetic moment value at 3 K is found to be 2.54 μB. Electrical resistivity increases tremendously below TN to an insulating state and shows thermal hysteresis near TN in zero field. Large magnetic fields drive insulator to metal-like transition and negative colossal magnetoresistance of about 70% is realized at 50 K in 70 kOe field and that could be due to the field-induced order.

Triethylamine-templated nanocalix Ln12 clusters of diacylhydrazone: crystal structures and magnetic properties

Three {Ln12} (Ln = Gd (1), Tb (2), Dy (3)) nanocalix clusters with a novel ligand of N,N'-bis(o-vanillidene)-1H-imidazole-4,5-dicarbohydrazide (H5ovih) were synthesized via the amine-templating strategy. The skeletal structures of these clusters were constructed from three symmetric {Ln4} units via the linkage of three V-type ligands, with a calix shape, which has not been reported previously. Complex 1 exhibited a clear magnetocaloric effect (MCE), whose maximum -ΔSm value reached 36.77 J kg-1 K-1 at 70 kOe and 2.0 K.

Tunable Curie temperature and magnetocaloric effect of FeCrMoCBYNi bulk metallic glass with different crystallized phases

The investigation on Curie temperature and magnetocaloric effect of the FeCrMoCBYNi bulk metallic glass (BMG) with different crystallized phases was carried out by XRD, TEM and PPMS. The experimental results show that the Curie temperature (Tc) of Fe45Cr15Mo14C15B6Y2Ni3 BMG with different annealing condition reaches a highest value of 95 K. The value of magnetic entropy change ΔSM (T) of Sample 3 reaches a maxima of 0.48 J/(kg·K) at Tc temperature, which result from the interaction among the precipitated phases of (Fe,Cr)23(C,B)6, Fe3Mo3C and residual amorphous phase. Based on the experiment results, it can be obtained that the Curie temperature, magnetocaloric effect can reach their optimal value at low temperature, when the content of amorphous phase and precipitated phases type run up to certain value. The magnetic properties of Sample 1 with full amorphous phase and Sample 4 with full crystalline phase will both decrease.

Magnetothermal properties of iron-based amorphous alloys type of Fe63.5M10Si13.5B9Nb3Cu1 (M = Cr, Mn, Fe, Co, Ni)

The magnetocaloric effect of amorphous Finemet alloys modified with 3d-transition metals was studied. In the alloys Fe63.5M10Si13.5B9Nb3Cu1 (M = Cr, Mn, Fe, Co, Ni), iron substitution per chromium or manganese leads to a significant decrease the Curie temperature and maximum value of the magnetic entropy change, while the substitution of iron with cobalt or nickel is not accompanied such substantial changes. The maximum value of ΔSm under magnetic field change ΔH = 15 kOe reduces significantly at Fe substitution by Cr or Mn atoms, and it decreases slightly at substitution by Co or Ni atoms.

Martensitic transformation and magnetic properties in Mn49−xCuxNi41Sn10(x = 0–2)

The crystal structure, phase transition, metamagnetic behavior and magnetic entropy change (ΔSM) of the Mn49−xCuxNi41Sn10(x = 0–2) alloys were systematically studied. The results of experiment about crystal structure confirm that Mn49−xCuxNi41Sn10 alloys have a highly ordered cubic L21 Heusler structure. With Cu element improving, all samples have a martensitic transformation and inverse martensitic transformation by analyzing the result of magnetic measurement. The saturation magnetization of samples decreases gradually, the martensitic transformation temperature (TM) of as-annealed samples increases to a high-temperature area, and the Curie temperature (TC) of samples moves to a low-temperature area with the content of Cu element increasing from x = 0 to x = 2. The positive values of magnetic entropy change (ΔSM) of all alloys were investigated near the martensitic transformation. When the applied magnetic field is 3 T, a worthwhile value of ΔSM can reach up to 32.0 J·kg−1·K−1 in Mn47Cu2Ni41Sn10 alloy.

Structural and magnetic properties with reversible magnetocaloric effect in PrSr1–xPbxMn2O6 (0.1 ≤ x ≤ 0.3) double perovskite manganite structures

ABSTRACTIn this study, the effect of Pb substitution with Sr on structural, magnetic and magnetocaloric properties in Pr(Sr1–xPbx)Mn2O6 (0.1 ≤ x ≤ 0.3) double perovskite manganite compounds prepared by the sol–gel method has been reported. Crystallinity has been worked by X-ray diffraction measurement and the Rietveld refinement method, which shows all samples are in monoclinic structure with P21/n space group without impurity phase. Scanning electron microscope analysis shows that all samples constituted from square-shaped grains with distinct grain boundaries, and energy-dispersive X-ray spectroscopy analysis shows that all expected elements are detected and there is no impurity element in the sample. All samples exhibit a magnetic phase transition from ferromagnetic to paramagnetic phase at TC determined as 274, 282 and 286 K for x = 0.1 (PSPM-1), 0.2 (PSPM-2) and 0.3 (PSPM-3) in the PrSr1–xPbxMn2O6 structure, respectively. Isothermal magnetisation curves near TC are used to determine the nature of the magnetic phase transition and the magnetic entropy change values (−ΔSM), which are found as 2.78, 3.11 and 3.52 J kg−1 K−1 for PSPM-1, PSPM-2 and PSPM-3 samples, respectively. Relative cooling power (RCP) values of the samples are also determined as 241, 311 and 246 J kg−1 for PSPM-1, PSPM-2 and PSPM-3 samples, respectively. ΔSM and RCP values are also calculated by using the Landau theory and the results are in accordance with the experimental results, which indicate the role of electron condensation energy and magneto-elastic coupling in magnetic entropy change value of the samples.

(La0.8Gd0.2)0.85Ag0.15MnO3 Perovskit Manganit Sisteminde Gd Yer Değiştirmesinin Yapısal Manyetik ve Manyetokalorik Özellikleri Üzerine Etkisi

In this paper, the effect of Gd substitution with La on structural, magnetic and magnetocaloric properties in (La0.8Gd0.2)0.85Ag0.15MnO3 manganite sample prepared by sol-gel method has been studied. The crystal properties have been investigated by x-ray diffraction technique that shows the sample is in rhombohedral structure with Rc space group. In addition to this structure, small amount of reflections belongs to GdMn2O5 phase is detected. Scanning electron microscope images show that the sample is constituted from square shaped grains. Energy dispersive x-ray spectroscopy analysis shows that the sample includes all expected elements. The sample exhibits magnetic phase transition from ferromagnetic to paramagnetic phase at around 149 K temperature. Applied field dependence of magnetization under isothermal process M(H) shows that the nature of the phase transition is second order and maximum magnetic entropy change (-ΔSM) value calculated from M(H) curves is found as 1.73 J/kgK under 50 kOe external magnetic field change.

Observation of Room-Temperature Range Magnetocaloric Effect in PrSr1−xPbxMn2O6 (0.4 ≤ x ≤ 0.6) Double-Perovskite Manganite System

The Pr(Sr1−xPbx)Mn2O6 (0.4 ≤ x ≤ 0.6) double-perovskite manganite samples have been produced by using a sol-gel method. The Rietveld refinement method has been used to analyse the structural properties, and the results show that all samples are crystallized in monoclinic structure with P21/n space group without any impurity phase. The temperature dependence of magnetization measurement shows that samples exhibit paramagnetic to ferromagnetic phase transition by decreasing temperature. The values of the $T_{\mathrm {C}}$ are determined as 286, 280 and 278 K for $x =$ 0.4, 0.5 and 0.6 in Pr(Sr1−xPbx)Mn2O6 samples, respectively. Isothermal applied magnetic field-dependent magnetization curves are used to determine both order of magnetic phase transition and magnetic entropy change (ΔSM) value. $-$ ΔSM values are found as 3.68, 3.15 and 2.85 J kg− 1 K− 1 for PSPM-4, PSPM-5 and PSPM-6 samples, respectively. Additionally, magnetic phase transition of the samples is identified as second-order magnetic phase transition that indicates accompanying small thermal and magnetic hysteresis to the samples during the phase transition. Relative cooling power (RCP) values are determined as 282, 233 and 268 J kg− 1 for PSPM-4, PSPM-5 and PSPM-6 samples, respectively.

Study of magneto-structural phase transitions and magnetocaloric effects in Co-based Heusler alloys synthesized via mechanical milling

In the present study, the effect of complete replacement of Cr by Fe dramatically enhances the structural, magnetic and magnetocaloric effect (MCE) of Co2(Cr1−xFex)Al (x = 0 and 1) Heusler alloys was studied. The present Heusler alloy systems were successfully prepared by mechanical alloying via high energy ball milling technique. Evolution of the B2 type disordered phase along with A2 type structure has been observed through X-ray diffraction. The substitution of Fe would lead to the development of remarkable enhancement of MCE observed near room temperature. The magnetic entropy (ΔSM) values of 10.77 J/kg-K and 17.46 J/kg-K, and refrigerant capacity (RC) 136.31 mJ/cm3 and 30.30 mJ/cm3 respectively are observed under an applied field of 20 kOe. The increment in magnetic entropy and refrigeration capacity with increasing Fe was associated with variation in lattice defects, and the presence of small amounts of magnetic/nonmagnetic secondary phases. Therefore, the increment in magnetic properties of these alloys was attributed to the enhancement of d-d exchange interaction due to the possible occupancy of vacant sites by Fe atoms, which indicates the development of relative anisotropy.

Effect of heat treatment procedure on magnetic and magnetocaloric properties of Ni43Mn46In11 melt spun ribbons

The effect of heat treatment on the structural, magnetic and magnetocaloric properties of Ni43Mn46In11 melt-spun ribbons was systematically investigated using X-ray powder diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), magnetic force microscope (MFM) and magnetic measurements. From the XRD studies, tetragonal and cubic phases were detected at room temperature for as-spun, quenched and slow-cooled ribbons. Furthermore, it was observed, upon annealing martensite transition temperatures increased when compared to the as-spun ribbon. To avoid magnetic hysteresis losses in the vicinity of the structural transition region, the magnetic entropy changes-ΔSm of the investigated ribbons were evaluated from temperature-dependent magnetisation-M(T) curves on cooling for different applied magnetic fields. The maximum ΔSm value was found to be 6.79 J kg−1 K−1 for the quenched ribbon in the vicinity of structural transition region for a magnetic field change of 50 kOe.

Single‐Molecule Magnet and Magnetothermal Properties of Two‐Dimensional Polymers Containing Heterometallic [Cu5Ln2] (Ln = GdIII and DyIII) Motifs

The reaction of a compartmental ligand N,N′‐bis(3‐methoxysalicylidene)‐1,3‐diamino‐2‐propanol (LH3) with CuII and LnIII salts under solvothermal conditions afforded two‐dimensional coordination polymers, [{Cu5Gd2(L)2(µ3‐OH)4(NO3)4(µ‐OH2)2}(NO3)2]∞ (1) and [{Cu5Dy2(L)2(µ3‐OH)4(NO3)4(MeOH)2}(NO3)2]∞ (2). A detailed study of the magnetic properties of the two coordination polymers reveals that the [Cu5Dy2] analogue shows single‐molecule magnet (SMM) behavior with an energy barrier of about 12 K with τ0 = 10–6 s under zero‐dc field, while the [Cu5Gd2] analogue shows magnetocaloric effect with a –ΔSm value of 17.55 J kg–1 K–1 at T = 2 K (ΔB = 5 T). Interestingly, the magnetic and SMM properties of the previously reported molecular and one‐dimensional analogues containing the [Cu5Ln2] motif are preserved even in the two‐dimensional coordination networks.

Magnetic properties and magnetocaloric effects of RNiSi2 (R= Gd, Dy, Ho, Er, Tm) compounds

Orthorhombic CeNiSi2-type polycrystalline RNiSi2 (R=Gd, Dy, Ho, Er, Tm) compounds were synthesized and the magnetic and magnetocaloric properties were investigated in detail. The transition temperatures of RNiSi2 compounds are all in a very low temperature range (<30 K). As temperature increases, all of the compounds undergo an AFM to PM transition (GdNiSi2 at 18 K, DyNiSi2 at 25 K, HoNiSi2 at 10.5 K, ErNiSi2 at 3 K and TmNiSi2 at 3.5 K, respectively). ErNiSi2 compound shows the largest (ΔSM)max (maximal magnetic entropy change) among these compounds. The value of (ΔSM)max is 27.9 J/kgK under a field change of 0-5 T, which indicates that ErNiSi2 compound is very competitive for practical applications in low-temperature magnetic refrigeration in the future. DyNiSi2 compound shows large inverse MCE (almost equals to the normal MCE) below the TN which results from metamagenitic transition under magnetic field. Considering of the normal and inverse MCE, DyNiSi2 compound also has potential applications in low-temperature multistage refrigeration.