ΔSM Peak Research Articles

Magnetocaloric effect and nature of magnetic transition in low dimensional DyCu2

In this manuscript, we propose a method to prepare small flakes of DyCu2. On top of that we also report on the magnetocaloric effect and nature of magnetic transition of a strongly anisotropic DyCu2 in its low dimension. Magnetization measurements were carried out in the temperature range of 5–100 K and up to the maximum magnetic field strength of 50 kOe. Magnetic entropy change (ΔSM) is estimated using the well-known Maxwell’s equations and is found to be −4.31 J/kg-K. Indeed, the ΔSM peak broadened marginally compared with its bulk DyCu2 and such a broadening can be attributed to significant increase in the total grain boundary volume. As these small flakes consists larger ΔSM values at temperatures higher than the Nèel temperature (TN), one can use them as a magnetic refrigerant material in a broad temperature range. We also plotted the M2 vs. H/M (which are called as the Arrott plots) in order to find the nature of magnetic transition. Arrott plots infer that indeed there exists nonlinearity in M2 vs. H/M behavior and such nonlinear behavior is ascribed to the random anisotropy or a random field that is present in the system.

Thermal stability, magnetic properties and large refrigerant capacity of ternary Gd55Co35M10 (M = Mn, Fe and Ni) amorphous alloys

Ribbon-shaped amorphous alloys with nominal compositions Gd55Co35M10 (M = Mn, Fe and Ni) have been successfully prepared and their thermal, magnetic and magnetocaloric properties were investigated. A large reduced glass transition temperature (Tg/Tm) (>0.60) are found in Gd55Co35M10 amorphous alloys. The relatively high Tx1/Tm and small Tm confirm the excellent glass forming ability of these alloys. The Curie temperatures (TCs) of the amorphous alloys Gd55Co35M10 with M = Mn, Fe and Ni are 197, 268 and 192 K, respectively. Under an applied field change of 2 T, the maximum values of magnetic entropy change (−ΔSM)max for Gd55Co35Mn10, Gd55Co35Fe10 and Gd55Co35Ni10 are 3.03, 1.72 and 3.37 J kg−1 K−1, while the values of refrigerant capacity (RC) are 224, 337 and 253 J kg−1, respectively. The large RC for Gd55Co35Fe10 is due to the broad (−ΔSM) peak (∼200 K), which is higher than that of the well-known crystalline Gd5Si2Ge2. Large RC and a considerable (−ΔSM) jointly make Gd55Co35M10 (M = Mn, Fe and Ni) amorphous alloys attractive candidates for magnetic refrigerant.

Magnetocaloric effect of the ternary Dy, Ho and Er platinum gallides

Magnetic and magnetocaloric properties of equiatomic ternary gallides RPtGa (R=Dy, Ho and Er) compounds have been reported. All these compounds are iso-structural and order antiferromagnetically below 20K. External applied magnetic field induces metamagnetic transition from antiferromagnetic to ferromagnetic state. Adiabatic entropy change (−ΔSM) shows negative contribution for magnetic field changes up to 10kOe (for R=Ho and Er) and 30kOe (for R=Dy) due to disordering of antiparallel spins with the external applied field. As the field change increases, only a positive asymmetric peak is observed. A broad −ΔSM peak is observed for HoPtGa, evidencing characteristics of a table-like behavior. HoPtGa and ErPtGa present the largest magnetocaloric effect (EMC) compared with DyPtGa, indicating that the nature of metamagnetic transition affects the magnetocaloric properties. The maximum value of adiabatic temperature change ( ∆Tadmax) obtained for R=Dy, Ho and Er was respectively 4.1K, 4.9K and 6.7K for ΔH=50kOe. These values are comparable with the respective ∆Tadmax reported for other RTX compounds in the same range of temperature and suggest that RPtGa compounds are attractive candidates for magnetic refrigeration in low temperature range (<20K) with the advantage of not presenting hysteresis loss.

Table-like magnetocaloric effect in Gd56Ni15Al27Zr2 alloy and its field independence feature

In order to obtain “table-like” magnetocaloric effect (MCE), multiple-phase Gd56Ni15Al27Zr2 alloy was prepared by arc-melting followed by suck-casting method. Powder x-ray diffraction and calorimetric measurements reveal that the sample contains both glassy and crystalline phases. The fraction of the glassy phase is about 62%, estimated from the heat enthalpy of the crystallization. The crystalline phases, Gd2Al and GdNiAl further broadened the relatively wider magnetic entropy change (−ΔSM) peak of the amorphous phase, which resulted in the table-like MCE over a maximum temperature range of 52.5 K to 77.5 K. The plateau feature of the MCE was found to be nearly independent of the applied magnetic field from 3 T to 5 T. The maximum −ΔSM value of the MCE platforms is 6.0 J/kg K under applied magnetic field change of 5 T. Below 3 T, the field independence of the table-like feature disappears. The relatively large constant values of −ΔSM for the respective applied magnetic fields have promising applications in magnetic refrigeration using regenerative Ericsson cycle.

Magnetocaloric Properties of Melt-Spun Fe–Ni–Mn–Ga Ribbons

The effects of Ni substitution for Fe on phase constitutions, Curie temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> , and magnetocaloric properties of melt-spun Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50-x</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">25</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">25</sub> (x = 0, 1, 3, 5 and 7) ribbons have been investigated. X-ray diffraction results show that the main phase in the Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50-x</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">25</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">25</sub> (x = 0-7) alloy changed with the increase of Ni content from FCC structure for x = 0 into B2 structure for x = 1-7. Besides, the magnetic phase exhibits phase transition of ferromagnetic into paramagnetic state with increasing temperature for the samples with B2-type structure. The Curie temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> of these ribbons varies in the temperature range of 232-257 K. The peak values of the maximal magnetic entropy change, -ΔS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sup> , are about 1.4-1.6 Jkg/K for Ni-substituted ribbons at a maximum applied field of 30 kOe. On the other hand, the relatively broader temperature range at the half maximum of ΔS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> peak (~ 90 K), low-cost and nontoxic elements make Fe-Ni-Mn-Ga-based ribbons the promising candidates for magnetic refrigeration applications close to room temperature.

Magnetocaloric Effect in LaFe10.7Co0.8Si1.5 Compound Near Room Temperature

Magnetocaloric properties of LaFe10.7Co0.8Si1.5 with the cubic NaZn13-type structure were investigated around their Curie temperature TC. By the help of the phenomenological model, the magnetization curves for LaFe10.7Co0.8Si1.5 at several magnetic fields were simulated. The magnetic entropy change and specific heat are obtained. The values of maximum magnetic entropy change, full-width at half-maximum, and relative cooling power, at several magnetic field variation, were calculated. It is shown that for LaFe10.7Co0.8Si1.5 the magnetic entropy change follows an asymmetrical broadening of ΔSM peak with increasing field. The maximum magnetic entropy change of this compound is 7.10 JK−1 kg−1 and relative cooling power is 201.37 J/K under a magnetic field of 2 T. The magnetocaloric effect of this material is large and tunable, suggesting a possible technical application of the material at moderate magnetic fields near room temperature.

The substitution effect of chromium on the magnetic properties of (Fe1−xCrx)80Si6B14 metallic glasses (0.02≤x≤0.14)

Magnetization studies were carried out to characterize the magnetic properties of the Iron-rich metallic glasses (Fe1−xCrx)80Si6B14 with 0.02≤x≤0.14. The Curie temperature TC diminishes almost linearly with the increase in the Cr-content from 401K (x=0.10) to 291K (x=0.14), while the saturation magnetization MS at T=5K also undergoes a linear reduction from 169Am2kg−1 (x=0.02) to 87Am2kg−1 (x=0.14). These results suggest that the system should become paramagnetic for x≈0.22. The magneto-caloric properties of samples with TC near room temperature, i.e., with x=0.12 and 0.14, were investigated up to a maximum magnetic field change of 8T. Both ribbons are characterized by a very broad temperature dependence of the magnetic entropy change ΔSM(T) and moderate peak values of 2.9Jkg−1K−1 and 2.6Jkg−1K−1, respectively.

Magnetocaloric Effect of Perovskite Eu0.5Sr0.5CoO3

Magnetocaloric properties of the Eu0.5Sr0.5CoO3 system near a phase transition from a ferromagnetic to a paramagnetic state are investigated. It is shown that the magnetic entropy change (ΔSM) peak spanning over a broad range of temperature leads to a remarkably wide working temperature region, yielding a significant performance in terms of refrigerant efficiency. Moreover, ΔSM distribution is very uniform, which is desirable for Ericsson-cycle magnetic refrigerator. Eu0.5Sr0.5CoO3 can be used as a working material of an apparatus based on the active magnetic regenerator cycle that cools hydrogen gas.

Phase evolution and magnetocaloric effect of melt-spun Mn3Sn2−xMx (M = B, C; x = 0–0.5) ribbons

The effects of B and C substitution for Sn on phase components, Curie temperature TC, and magnetocaloric effect of melt-spun Mn3Sn2-xMx (M = B, C; x = 0−0.5) ribbons have been investigated. X-ray diffraction (XRD) results show that the main phase in the as-spun Mn3Sn2−xMx (M = B, C; x = 0−0.5) ribbons is Mn3Sn2 of Ni3Sn2-type (Pnma). Minor Mn2B (when x ≥ 0.1) or Mn5C2 (when x &amp;gt; 0.1) secondary phase is formed, and their amounts increase with increasing B and C concentration, respectively. The Curie temperature TC of these ribbons varies in the temperature range of 240−250 K. The peak values of the maximal magnetic entropy change, −ΔSMmax, are about 13.6−18.3 mJ/cm3 K for B-substituted ribbons and 13.6–17.5 mJ/cm3 K for C-substituted ribbons, respectively, at a maximum applied field of 50 kOe. These values are about one fifth that of Gd (81.4 mJ/cm3 K). However, the relatively broader temperature range of the half maximum of ΔSM peak (∼100 K), low-cost and nontoxic elements still make Mn3Sn2-based ribbons the promising candidates for magnetic refrigeration applications close to room temperature.

Magnetic properties and magnetocaloric effect in La0.7Nd0.3Fe13−xSix compounds

The structural, magnetic and magnetocaloric properties in the cubic NaZn13-type La0.7Nd0.3Fe13−xSix compounds with x=1.2, 1.4, 1.6 and 1.8 are reported. All of the investigated samples are ferromagnetically ordered. The Fe saturation moment at 5K is independent of Si concentration, having a value of 2.05±0.09μB, which suggests a high degree of localization. The Curie temperatures increase almost linearly with the increase in silicon concentration. The large ΔSM values obtained for samples with low Si content are mainly due to the first-order character of the transition at TC. The field-induced transition above TC causes an asymmetric broadening of the ΔSM peak towards higher temperatures for higher applied fields. With increasing Si content, the first-order character of the transition at TC is diminished, leading to lower ΔSM values. The potential use of these materials in magnetic refrigeration is discussed.

Tunable magnetocaloric effect in Gd-based glassy ribbons

The series of glassy ribbons Gd60M30In10 (M = Mn, Co, Ni, Cu) was synthesized by melt-spinning. The change of transition element M in these Gd-based metallic glasses was proven to induce huge variations of the Curie temperature TC, magnetic entropy change peak values ΔSmpeak, and widths at half maximum values of the magnetic entropy change δT. When M is non magnetic (M = Co, Ni, Cu), the samples behave similarly: they display high values of ΔSmpeak (between -6.6 and -8.2 J/kg K in a magnetic field variation of 4.6 T), average δT values (between 77 and 120 K) and no magnetic hysteresis. On the contrary, when M carries a magnetic moment (M = Mn), some irreversibility appears at low temperature, ΔSmpeak is lower (only 3.1 J/kg K for μ0H = 4.6 T) and the magnetic transition is very large (δT = 199 K for μ0H = 4.6 T). These features are explained by some antiparallel coupling between Mn atoms randomly located in the metallic glass. This leads to the occurrence of a cluster-glass behavior at low temperature (35 K), following the ferromagnetic transition observed at 180 K when the temperature is decreased. Also, power law fittings of ΔSmpeak and δT versus μ0H were performed and show that δT is less field dependent than ΔSmpeak. We could then identify an interesting way of improving the refrigeration capacity of the material at low magnetic field.

Magnetocaloric effects in RNiIn (R = Gd-Er) intermetallic compounds

Magnetic properties and magnetocaloric effects (MCEs) of the intermetallic RNiIn (R = Gd-Er) compounds have been investigated in detail. GdNiIn and ErNiIn compounds exhibit a ferromagnetic (FM) to paramagnetic (PM) transition around the respective Curie temperatures. However, it is found that RNiIn with R = Tb, Dy, and Ho undergo two successive magnetic phase transitions with increasing temperature. In addition, a field-induced metamagnetic transition from antiferromagnetic (AFM) to FM states is observed in RNiIn with R = Tb and Dy below their respective AFM-FM transition temperatures (Tt). The maximal values of magnetic entropy change (ΔSM) of HoNiIn are –9.5 J/kg K at Tt = 7 K and –21.7 J/kg K at TC = 20 K for a magnetic field change of 5 T, respectively. These two successive ΔSM peaks overlap partly, giving rise to a high value of refrigerant capacity (RC = 341 J/kg at 5 T) over a wide temperature span. It is noted that the RC value of GdNiIn is as high as 326 J/kg due to the relatively broad distribution of ΔSM peak. Consequently, this RNiIn system shows large reversible ΔSM and considerable RC values in the temperature range of 10–100 K.

The influence of Si addition on the glass forming ability, magnetic and magnetocaloric properties of the Gd-Fe-Al glassy ribbons

The effects of Si substitution for Al on the glass forming ability, Curie temperature TC, magnetocaloric effect, and refrigeration capacity (RC) of melt-spun Gd-based Gd65Fe20Al15−xSix (x = 0–7) glassy ribbons have been investigated. The small amounts of Si substitution for Al in the Gd65Fe20Al15−xSix glassy ribbons with high Tx/Tm (&amp;gt; 0.70) and small ΔTm (ΔTm = Tm−Tx) promote the formation of high thermal stability of these alloys. The Si addition leads to an increase of Curie temperature TC of glassy ribbons from 181 K for x = 0 to 227 K for x = 7. The maximal magnetic entropy changes −ΔSM and RC values for magnetic field change of 50 kOe are about 4.70–5.20 J/kg K and 710–760 J/kg, respectively. The large RC values are due to the broad temperature range of the half maximum of ΔSM peak (∼ 200 K), which is caused by the change of the amorphous disorder structure. The moderate ΔSM and large RC values jointly make the Gd65Fe20Al15−xSix glassy ribbons promising candidates for magnetic refrigeration materials working at temperature range of 100–300 K.

Magnetic entropy change and large refrigerant capacity of Ce6Ni2Si3-type GdCoSiGe compound

Magnetic entropy change (ΔSM) and refrigerant capacity (RC) of Ce6Ni2Si3-type Gd6Co1.67Si2.5Ge0.5 compounds have been investigated. The Gd6Co1.67Si2.5Ge0.5 undergoes a reversible second-order phase transition at the Curie temperature TC = 296 K. The high saturation magnetization leads to a large ΔSM and the maximal value of ΔSM is found to be 5.9 J/kg · K around TC for a field change of 0–5 T. A broad distribution of the ΔSM peak is observed and the full width at half maximum of the ΔSM peak is about 101 K under a magnetic field of 5 T. The large RC is found around TC and its value is 424 J/kg.

Structural, magnetic, electrical transport properties, and reversible room-temperature magnetocaloric effect in antipervoskite compound AlCMn3

We report the structural, magnetic, electrical transport properties, and magnetocaloric effect (MCE) of antipervoskite compound AlCMn3. It exhibits a second-order ferromagnetic–paramagnetic phase transition around (TC) 287 K. The electronic resistivity (ρ) shows a good metallic behavior except for a slope change around TC. At lower temperatures (below 130 K), ρ∝T2 indicates that the electron-electron scatterings domain. At evaluated temperatures (130–270 K), ρ is linear dependence on temperature, implying that the phonon scatterings boost up greatly. Furthermore, a broad distribution of the magnetic entropy change (−ΔSM) peak is found to about 100 K with the magnetic field change ΔH=45 kOe. The relative cooling power are ∼137 J/kg and ∼328 J/kg (or ∼68 K2 and ∼162 K2) with ΔH=20 kOe and 45 kOe, respectively. All these values are comparable with the typical MCE associated with a second-order transition. It suggests that AlCMn3 may be considered as a candidate material for near room-temperature magnetic refrigeration because of: (i) the large full width at half peak of the −ΔSM-T curve, (ii) no hysteresis losses, (iii) the near room-temperature working temperature, and (iv) the low-cost and innoxious raw materials. Moreover, it is found that the simple theoretical model which only considering the magnetoelastic and magnetoelectronic couplings couldn’t account well for the observed MCE in antiperovskite AlCMn3.

Room-temperature large refrigerant capacity of Gd6Co2Si3

The magnetic properties and magnetocaloric effects of the Gd6Co2Si3 alloy are investigated. Gd6Co2Si3 undergoes a reversible second-order magnetic transition with a Curie temperature at room temperature (TC=295 K). A broad distribution of the magnetic entropy change ΔSm peak is observed, and the full width at half maximum of the ΔSm peak is found to be about 111 K under a magnetic field of 5 T. The large value of the refrigerant capacity (RC) is found to be comparable with those of pure Gd, which have maximal RC values for all the magnetocaloric materials reported previously. The maximal value of ΔSm is 6.3 J/kg K for a field change of 0–5 T. Excellent magnetocaloric properties, especially considerable values of RC, indicate the applicability of Gd6Co2Si3 for magnetic refrigeration in the room-temperature range.

Colossoal magnetoresistance and large magnetic entropy change in La2/3Ca1/3Mn1-xSix O3 (x = 0.05–0.20) manganites

Magnetotransport and magnetocaloric properties of polycrystalline La2/3Ca1/3Mn1-xSixO3 (x = 0.05, 0.10, 0.15 and 0.20) have been studied. The colossal magnetoresistance (CMR) effect and large magnetic entropy change (ΔSM) have been found in the vicinity of Curie temperature (TC). With the increases of Si content x, the MR and ΔSM peak positions as well as TC gradually shift to low temperatures, while MR peak value gradually increases from 84% to 140%, and the maximum value of magnetic entropy change remains nearly the same high value, in the range of 8.4 − 9.6 J Kg−1 K−1 for a magnetic field variation of 6 T.

Large magnetocaloric effect in La2/3Ca1/3Mn1−xSixO3 (x = 0.05–0.20) manganites

The magnetocaloric effect (MCE) in Mn site Si substituted La2/3Ca1/3Mn1−xSixO3 (x = 0.05, 0.10, 0.15 and 0.20) was investigated. All the samples have a single paramagnetic to ferromagnetic transition and show a large magnetic entropy change (−ΔSM) in the vicinity of the Curie temperature (TC). With the increases in Si content x, the −ΔSM peak position as well as TC gradually shift to a low temperature, while the maximum value of the magnetic entropy change remains at nearly the same high value, in the range 4.88–5.48 J Kg−1 K−1 and 8.78–10.32 J Kg−1 K−1 for a magnetic field variation of 2 T and 7 T, respectively. The origin of the large MCE and its potential application were discussed. The present system appears to be a good candidate for magnetic refrigerant materials.

Large magnetocaloric effect and enhanced magnetic refrigeration in ternary Gd-based bulk metallic glasses

The magnetocaloric effect and refrigeration capacity (RC) of Gd55Co20Al25 and Gd55Ni25Al20 bulk metallic glasses (BMGs) have been investigated. Large magnetic entropy changes ΔSM of 11.2 and 10.8 J kg−1 K−1 and large RC values of 846 and 920 J kg−1 are obtained for Gd55Co20Al25 and Gd55Ni25Al20, respectively, at a field change of 7 T. The RC value (640 J kg−1 at 5 T or 920 J kg−1 at 7 T) of Gd55Ni25Al20 BMG is larger than that reported for all magnetocaloric materials, including crystalline and amorphous materials measured under the same conditions. The large RC value is due to the broad ΔSM peak (more than 100 K), which is caused by the disordered structure of an amorphous material. The large ΔSM and RC values make these Gd-based ternary BMGs attractive candidates for magnetic refrigeration applications.

Structure and magnetocaloric properties of the Fe-doped HoTiGe alloy

The structure and magnetocaloric properties of the Fe-doped HoTiGe compound were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy, x-ray diffraction, magnetometry, and calorimetry. As with the early studies on the undoped compound, the Fe-containing alloy exhibited an antiferromagnetic-to-paramagnetic transition and a magnetocaloric effect peak at 90K. The magnetization (M) versus temperature (T) data showed peaks at 10 and 90K, while M versus field (H) curves showed the presence of a field-induced transition for all T&amp;lt;120K; additionally, for all T&amp;lt;60K, open hysteresis loops at the magnetic transitions were observed. XRD measurements between 10 and 60K under various magnetic fields up to 3184kA∕m (40kOe) showed that the hysteresis was not accompanied by any change in crystallography. The magnetization derived entropy change −ΔSm vs T plot also showed the presence of two peaks, at 20 and 90K; but below 15K, −ΔSm increased steeply with decreasing temperature. It is believed that the minor phases in the Fe-doped alloy give rise to the magnetization-derived −ΔSm peak at 20K. The heat-capacity-derived −ΔSm vs T plot for the Fe-doped alloy also showed the presence of two peaks at 20 and 90K. However, the heat-capacity-derived −ΔSm did not show a rapid rise with decreasing temperature below 15K.