Large ΔSM Research Articles

Effect of Cu doping on the magnetic and magnetocaloric properties in the HoNiAl intermetallic compound

The magnetic properties and magnetocaloric effect of Cu doping on HoNiAl (HoNi1−xCuxAl) have been investigated. Two transitions occurred for samples with x=0 and x=0.1 induced by the combination and competition between antiferromagnetic (AFM) and ferromagnetic (FM) orderings. Simple AFM orderings were found in samples with x=0.2 to x=0.7 while FM orderings were found in samples with x=0.8–1. The magnetocaloric effect (MCE) was investigated in selected samples with x=0.3 and 0.8. Large magnetic entropy changes (ΔSM) as −29.2J/kgK at 9K and −19.7J/kgK at 9K with corresponding refrigerant capacity (RC) of 299J/kg, 309J/kg for a field change of 0–50kOe were observed. The large ΔSM and RC without hysteresis loss indicated these materials attractive candidates for magnetic refrigeration in low temperature range.

Appearance of Griffiths phase in La0.62Er0.05Ba0.33Fe0.2Mn0.8O3 manganite

Structural and magnetic properties of La0.62Er0.05Ba0.33Fe0.2Mn0.8O3 (LEBFMO) compound have been investigated. Rietveld refinement of powder X-ray diffraction data reveals that the sample crystallizes in the rhombohedral (R3¯c) structure. The dc and ac magnetic studies demonstrate aspects of Griffiths phase-like behavior above the Curie temperature. The observed anomalous paramagnetic behavior is attributed to the magnetic heterogeneity which is caused by the segregation of short-range ferromagnetic clusters within the paramagnetic matrix. A large deviation is usually observed between zero fields cooled (ZFC) and field cooled (FC) M(T) at a low temperature below the blocking temperature. At 50K a spin-glass state is seen to arise from a ferromagnetic state. This is caused by the competition between the ferromagnetic and antiferromagnetic interaction. From isothermal magnetization versus magnetic applied field, we deduced the magnetic entropy change ΔSM. The large RCP and ΔSM found in Fe-substituted sample are found to be interesting for magnetic refrigeration below room temperature.

Giant magnetic entropy change in manganese perovskite La0.67Sr0.16Ca0.17MnO3 near room temperature

Structural, magnetic and magnetocaloric properties of La0.67Sr0.16Ca0.17MnO3 perovskite have been studied. A solid state reaction method was used in the preparation phase. X-ray diffraction analysis using Rietveld refinement revealed that this sample crystallizes in the distorted rhombohedral system with R3‾c space group. The variation of magnetization (M) vs. temperature (T), under an applied magnetic field of 0.05T, revealed a transition from a ferromagnetic (FM) to paramagnetic (PM) phase at around Curie temperature (TC=336K). Using Arrott plots, it was found that the transition is of a second-order. Isothermal measurements of magnetization allow us, through thermodynamic Maxwell relations, to determine the magnetic entropy change (ΔSM). A large ΔSM deduced from isothermal magnetization curves, has been observed in our sample with a peak centered around its respective TC. The maximum of the magnetic entropy change ΔSMmax in a magnetic field change of 5T is found to be 5.51Jkg−1K−1 at 335K. In addition, the compound showed a large relative cooling power (RCP) value of about 234J/kg while the maximum refrigerant capacity of 174J/kg was attained at the applied field of 5T. As a result, the studied sample can be considered as a potential material for magnetic refrigeration.

Collapse of charge ordering and enhancement of magnetocaloric effect in La0.5Ca0.5−xAgxMnO3 (x = 0.0 and 0.2)

The present letter undertakes the analysis of the influence of the charge-ordering on the magnetic entropy change between La0.5Ca0.5MnO3 and La0.5Ca0.3Ag0.2MnO3 polycrystalline samples. The magnetic entropy change (ΔSM) of x=0 alters the sign from negative to positive with the decrease in temperature below the charge ordering. However, ΔSM is negative and exhibits a peak close to TC in Ag-doped samples. The large RCP and ΔSM found in Ag-substituted samples were found to be interesting for magnetic refrigeration below room temperature. The obtained results were discussed within the framework of charge ordering and its destruction with Ag substitution.

The influence of quench atomic disorder on the magnetocaloric properties of Ni–Co–Mn–In alloys

The magnetocaloric effect in Ni–Co–Mn–In alloys is studied at low magnetic field, across the first order magnetostructural transition. The Co doping at Ni site induces the large magnetic entropy change (ΔSm) above room temperature. The large ΔSm of 11J/KgK has been observed for disordered Ni1.81Co0.22Mn1.46In0.51 alloy at 337K at an applied field of 1.5Tesla. The influence of quench atomic disorder on the magnetocaloric properties of Ni–Co–Mn–In alloys has been studied. The atomic disorder significantly increases the peak value of ΔSm and decreases the peak width. The refrigeration capacity (RC) is almost unchanged with atomic disorder.

Effect of Particle Size on the Hysteretic Behavior and Magnetocaloric Effect of La0.5Pr0.5Fe11.4Si1.6 Compound

Bulk La0.5Pr0.5Fe11.4Si1.6 compound exhibits a large magnetic-entropy change ΔS m of 28.1 J/(kg K) for a magnetic-field change from 0 to 1.5 T at the Curie temperature, T C of 186 K, accompanied by a large magnetic hysteresis of 56 J/kg and a noticeable thermal hysteresis of about 1 K. If the bulk sample is ground into middle-size particles (30–60 μm), then the thermal hysteresis is almost eliminated and the magnetic hysteresis loss is decreased by 29%, while the large ΔS m maintains. Especially, fine powder with an average size of 2 μm shows the same T C as the bulk and does not lose stability. Meanwhile, a comparatively large ΔS m of 13.9 J/(kg K) and a hysteresis reduction of 70% are attained. The hysteresis reduction can be ascribed to the decrease of internal strains and to the improvement of heat transfer due to the increase of the ratio of the surface area to the volume.

Effect of Ce doping on the magnetic and magnetocaloric properties of Pr0.5Sr0.5−xCexMnO3 manganites

The magnetic and magnetocaloric effects of manganites of Pr0.5Sr0.5−xCexMnO3 (x = 0, 0.04, 0.08 and 0.1) prepared by standard solid-state reaction method are investigated. Large magnetic entropy changes (ΔSm) with the ferromagnetic–paramagnetic transition have been found. The ΔSm and Curie temperature (TC) gradually increase with increasing Ce content. The maximum of magnetic entropy change in a low magnetic change of 15 kOe is about −1.93 J kg−1 K−1 for x = 0.1 sample with a TC value of 310 K. Due to the large ΔSm and tunable TC around the room temperature, it is suggested that Pr0.5Sr0.5−xCexMnO3 could be used as desirable active room temperature magnetic refrigerants.

Low-field large reversible magnetocaloric effect in the RNi2Si2 (R=Dy, Ho, Er) compounds

The magnetocaloric effect (MCE) of RNi2Si2 (R=Dy, Ho, Er) compounds with the ThCr2Si2-type body-centered tetragonal structure are investigated. RNi2Si2 compounds are antiferromagnetic (AFM) with Néel temperature TN=6.5K, 4.9K, and 3.5K, respectively. A field-induced metamagnetic transition from AFM-to-ferromagnetic (FM) state is found below TN, which leads to a large MCE around the TN. The maximal values of magnetic entropy change (ΔSM) for RNi2Si2 (R=Dy, Ho, Er) reach −6.9, −10.9, and −15.1Jkg−1K−1 and −21.3, −21.7, and −21.3Jkg−1K−1 without thermal and magnetic hysteresis losses for the field changes of 0–2T and 0–5T, respectively. The large ΔSM is associated with the field-induced first-order AFM–FM metamagnetic transition and low critical field. The excellent MCE under low field change without hysteresis loss suggests that RNi2Si2 (R=Dy, Ho, Er) can be an appropriate candidate for magnetic refrigerant in liquid helium temperature ranges.

Magnetic entropy change and relative cooling power of Gd3Ni6Al2 and Tb3Ni6Al2 compounds

We present study of the magnetocaloric effects (MCE) in Gd3Ni6Al2 and Tb3Ni6Al2 crystallizing in the Cubic Ce3Ni6Si3-type structure. The two compounds undergo a second-order ferromagnetic transition at Curie temperature TC=105.7 and 57.5K for Gd3Ni6Al2 and Tb3Ni6Al2, respectively. Magnetization and specific heat are measured as functions of temperature and magnetic field around TC, and the measurements are used to estimate the magnetic entropy change (ΔSm) and the relative cooling power (RCP) by both magnetic and calorimetric techniques. A relatively large ΔSm associated with the ferromagnetic transition has been observed over a wide temperature range for both the compounds, leading to a high RCP. The maximum values of ΔSm in a 5T magnetic field are evaluated to be 6.2Jkg−1K−1 for Gd3Ni6Al2 and 9.8Jkg−1K−1 for Tb3Ni6Al2, the corresponding values of RCP are 608 and 461Jkg−1, respectively. Particularly, both Gd3Ni6Al2 and Tb3Ni6Al2 show higher RCP values even in a small field change that can be generated by a permanent magnet.

Enhancement of the refrigerant capacity in low level boron doped La0.8Gd0.2Fe11.4Si1.6

The effects of boron doping on the itinerant-electron metamagnetic (IEM) transition and the magnetocaloric effects (MCEs) in the cubic NaZn13-type La0.8Gd0.2Fe11.4Si1.6 compound have been investigated. The Curie temperature, TC, of La0.8Gd0.2Fe11.4Si1.6Bx compounds with x=0, 0.03, 0.06, 0.2 and 0.3 was found to increase from 200K to 222K with increase in boron doping, x. The maximum values of the isothermal magnetic entropy change, ΔSM, (derived using the Maxwell relation for a field change ΔB=0–5T) in La0.8Gd0.2Fe11.4Si1.6Bx with x=0, 0.03, 0.06, 0.2 and 0.3 are 14.8, 16, 15, 7.5 and 6.6Jkg−1K−1 respectively, with corresponding values of the refrigerant capacity, RCP of 285, 361, 346, 222 and 245Jkg−1. The large ΔSM values observed for the undoped sample, and the low level B doped La0.8Gd0.2Fe11.4Si1.6B0.03 and La0.8Gd0.2Fe11.4Si1.6B0.06 compounds are attributed to the first order nature of the IEM transition while the decrease of ΔSM at x=0.2 and 0.3 is due to a change in the second order phase transition with increase in B doping. The nature of the magnetic phase transitions is also reflected by the magnetic hysteresis of 3.7, 9, 5.7, 0.4 and 0.3Jkg−1 for x=0.0, 0.03, 0.06, 0.2 and 0.30 respectively. The possibility of tuning the TC and the magnetocaloric properties at temperatures close to room temperature make this system interesting from the points of view of both fundamental aspects as well as applications.

Magnetocaloric effect in La0.5Pr0.5Fe11.5Si1.5 compounds with a combined addition of Co and C

The influence of a combined addition of Co and C on the magnetocaloric effect in the La0.5Pr0.5Fe11.5Si1.5 compound is investigated. The addition of Co and C can adjust Curie temperature (TC) to around room temperature. Although the magnetic entropy change (ΔSM) of La0.5Pr0.5Fe11.5−xCoxSi1.5C0.2 decreases with the increase of x, the maximum hysteresis loss at TC reduces remarkably from 23.6 J/kg for x = 0 to close to zero for x = 0.2. For x = 0.8, the maximum value of ΔSM is −11.6 J/kg K with an RC value of 386 J/kg around TC = 295 K for a magnetic field change of 0-5 T. Our result reveals that a large ΔSM and a small hysteresis loss can be simultaneously achieved in NaZn13-type LaPrFeSi compounds with a combined addition of Co and C.

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.

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.

Magnetocaloric effect and magnetic phase transition in Ho3Co

Magnetocaloric effect (MCE) and magnetic phase transition of Ho3Co compound have been investigated. The two successive magnetic transitions: spin–reorientation transition at TSR = 8.5 K and antiferromagnetic (AFM)–paramagnetic transition at the Néel temperature TN = 21 K are observed. The Ho3Co compound undergoes a field-induced metamagnetic transition from AFM to ferromagnetic states below TN, which leads to a large MCE. The maximal value of magnetic entropy change (ΔSM) is found to be −14.5 J/kg K with a refrigerant capacity (RC) value of 440 J/kg around TN for a field change of 0–5 T. The large ΔSM as well as considerable RC in Ho3Co is very useful for applying it to the magnetic refrigeration in low-temperature ranges.

Magnetic and calorimetric investigations of inverse magnetocaloric effect in Pr0.46Sr0.54MnO3

We investigated magnetic entropy change (ΔSm) in the A-type antiferromagnet Pr0.46Sr0.54MnO3 by magnetic and differential scanning calorimetry (DSC) methods. The field-induced antiferromagnetic to ferromagnetic transition is first-order in nature and is accompanied by a large change in the latent heat as evidenced by the DSC data. The ΔSm shows an inverse magnetocaloric effect (ΔSm=+9 J kg−1 K−1 for ΔH=7 T) around the Neel temperature (TN=210±2 K) by magnetic measurement, which closely agrees with the calorimetric results. It is suggested that the large positive ΔSm results from a field-induced structural transition that accompanies the destruction of antiferromagnetism.

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.

Changes in electronic states and magnetic free energy in La1−zCez(FexSi1−x)13 magnetic refrigerants

The influence of partial substitution of Ce on the electronic structure and magnetic free energy has been investigated for La1−zCez(FexSi1−x)13. From the Mössbauer spectroscopy of La0.7Ce0.3(Fe0.88Si0.12)13, the distribution of the electric field gradient is found to be scarcely changed, therefore, the volume reduction by partial substitution is regarded as isotropic. The change of the isomer shift to positive sign after the partial substitution is closely correlated with the 5d and/or 4f electrons of Ce.The change in magnetic free energy has been examined for La0.7Ce0.3(Fe0.86Si0.14)13 having a large magnetic entropy change ΔSm and a small hysteretic behaviour. From the results analysed by the Landau expansion theory, the large ΔSm and the small hysteresis of this compound are attributed to the magnitude and thermal variation of the fourth-order Landau coefficient in magnetic free energy. Consequently, the combination of partial substitution and control of Fe concentration is useful for highly efficient magnetic refrigerants.

Effect of impurity doping at the Mn-site on magnetocaloric effect in Pr0.6Ca0.4Mn0.96B0.04O3 (B=Al, Fe, Cr, Ni, Co, and Ru)

We report the effect of impurity doping at the Mn-site on magnetization and magnetic entropy change (ΔSm) in Pr0.6Ca0.4Mn0.96B0.04O3 with B cations having different electronic and spin states [B=Al3+(d0), Cr3+(d3), Fe3+(d5), Co2+(d7), Ni2+(d8), and Ru4+/5+(d4/3)]. The charge ordered antiferromagnetic insulator Pr0.6Ca0.4MnO3 transforms into a ferromagnetic metal in the absence of an external magnetic field (H) for B=Cr, Ni, Co, and Ru, whereas B=Fe and Al samples remain as antiferromagnetic insulators. It is found that the applied magnetic field induced an abrupt increase in the magnetization above a critical value of H (field-induced metamagnetic transition) in the paramagnetic state for B=Cr, Ni, and Co but not for B=Ru, which has the highest Curie temperature in the series (TC=205 K). The B=Co sample shows the maximum value of the magnetic entropy (−ΔSm=7.37 J/kg K under ΔH=5 T), which is followed by −ΔSm=6.77,6.0,5.07,5.04,2.72 J/kg K for B=Ni, Cr, Ru, Fe, and Al, respectively. We have also found a large magnetic entropy change (−ΔSm=8.42 J/kg K under ΔH=5) by differential scanning calorimetric study in B=Co sample. The large ΔSm values in B=Co, Cr, and Ni compared to Ru originate from the distinct field dependence of the magnetization above TC. It is suggested that both charge-orbital fluctuations and ferromagnetic polarons exist in the paramagnetic phase of B=Co, Cr, and Ni samples in the absence of a magnetic field, and the external magnetic field suppresses charge-orbital fluctuations and enhances size of ferromagnetic polarons, which leads to observed large ΔSm values. Our study suggests that creation of charge-orbital fluctuations and ferromagnetic polarons by dilution of the Mn-site could be a simple way to enhance the magnetocaloric effect in charge ordered manganites.

Large magnetic entropy change near room temperature in La0.7(Ca0.27Ag0.03)MnO3 perovskite

In this paper, the magnetic properties and magnetocaloric effect (MCE) of La0.7(Ca1−xAgx)0.3MnO3 (x=0, 0.1, 0.2, 0.7, and 1) powder samples are reported. Our polycrystalline compounds were synthesized using the solid state reaction method at high temperature. Magnetization measurements versus temperature showed that all our samples exhibited a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature, TC, has been found to increase from ∼250K for x=0–270K for x=1. Ag doping weakens the first order phase transition, and at higher Ag doping, the phase transition is of second order. For the La0.7(Ca0.27Ag0.03)MnO3 composition, the maxima of the magnetic entropy changes from the applied magnetic field (ΔSM) at 2 and 5T are about 4.5 and 7.75J/kgK, respectively, at the Curie temperature of ∼263K. The relative cooling power (RCP) values without hysteresis loss are about 102 and 271J/kg for the applied fields of 2 and 5T, respectively. Due to the large ΔSM, large RCP, and high Curie temperature, La0.7(Ca0.27Ag0.03)MnO3 is promising for application in potential magnetic refrigeration near room temperature.

Effect of Ru-substitution on electrical and magnetocaloric properties of [formula omitted

It is shown that the charge-orbital ordered antiferromagnetic insulating state of the parent compound (y=0) in Nd0.5Ca0.5Mn1−yRuyO3 (y=0, 0.03, 0.05, & 0.10) series is destabilized and a ferromagnetic metallic state is induced by Ru substitution as small as 3%. The ferromagnetic transition temperature (TC) increases with Ru content from 215 K (y=0.03) to 255 K (y=0.10). The magnetic entropy change (ΔSm) of y=0 changes sign from negative to positive as the temperature is lowered below the charge ordering temperature. However, ΔSm is negative and exhibits a peak close to TC in Ru-doped samples. The peak values of ΔSm are −0.33, −3.8, −3.6, and −3.5 J kg−1 K−1 for y=0, 0.03, 0.05, & 0.10 respectively, for a field change of ΔH=5 T. The relative cooling power (RCP) decreases with increasing Ru content from 268 J/kg for x=0.03 to 234 J/kg for x=0.10 for ΔH=5 T whereas the y=0 sample shows 17 J/kg. The large RCP and ΔSm found in Ru-substituted samples will be interesting for magnetic refrigeration below room temperature.