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In this paper, the magnetocaloric properties and magnetic phase transition of the (La–Ca) MnO3 system after secondary doping with the large magnetic moment rare earth element Gd are investigated. Analysis reveals that the polycrystalline material La0.65Ca0.3Gd0.05MnO3 exhibits a magnetocaloric effect superior to both the un-secondary doped and similar types of materials at the critical point of the ferromagnetic–paramagnetic phase transition (TC = 173 K). Under 7 T magnetic field, the maximum magnetic entropy change |∆SMmax|, refrigerant capacity RC, and relative cooling capacity RCP are 8.10 J kg−1 K−1, 350.54 J kg−1, and 422.17 J kg−1, respectively. The high overlap between TEC (4 K) and |∆SMmax| at the same magnetic field indicates its good utility. Landau theory yields a negative slope of the Arrott plot at TC, and the fit of Landau coefficients b (TC) obtains negative values verifying the ferromagnetic–paramagnetic first-order phase transition. Further calculation of the n value and the universal curve plot using the magnetocaloric effect confirmed this type of magnetic phase transition and revealed the origin of the large magnetocaloric effect. The material provides new ideas for applications in cryogenic magnetic refrigeration. [ABSTRACT FROM AUTHOR]

In this paper, the magnetocaloric properties and magnetic phase transition of the (La–Ca) MnO3 system after secondary doping with the large magnetic moment rare earth element Gd are investigated. Analysis reveals that the polycrystalline material La0.65Ca0.3Gd0.05MnO3 exhibits a magnetocaloric effect superior to both the un-secondary doped and similar types of materials at the critical point of the ferromagnetic–paramagnetic phase transition (TC = 173 K). Under 7 T magnetic field, the maximum magnetic entropy change |∆SMmax|, refrigerant capacity RC, and relative cooling capacity RCP are 8.10 J kg−1 K−1, 350.54 J kg−1, and 422.17 J kg−1, respectively. The high overlap between TEC (4 K) and |∆SMmax| at the same magnetic field indicates its good utility. Landau theory yields a negative slope of the Arrott plot at TC, and the fit of Landau coefficients b (TC) obtains negative values verifying the ferromagnetic–paramagnetic first-order phase transition. Further calculation of the n value and the universal curve plot using the magnetocaloric effect confirmed this type of magnetic phase transition and revealed the origin of the large magnetocaloric effect. The material provides new ideas for applications in cryogenic magnetic refrigeration. [ABSTRACT FROM AUTHOR]

In this current study, we present a detailed investigation on the structural, magnetic, magnetocaloric and electrical properties for La0.4Ag0.1Ca0.5MnO3 (S1) and La0.5Ca0.4Ag0.1MnO3 (S2) polycrystallines samples prepared using the well-known sol–gel method. Our analysis of X-ray diffraction, employing Rietveld refinement, reveals that these samples crystallize in the orthorhombic structure with Pnma space group. The results demonstrated that magnetization measurements as a function of temperature, under different magnetic fields for the sample (S1), exhibit two distinct phase transitions at TC1 = 48 K and TC2 = 186 K, whereas sample (S2) displays a single transition at 261 K. Based on the magnetic field dependence of magnetization, M(H), and applying the thermodynamic Maxwell equation, the magnetic entropy change |ΔSm| of the studied samples (S1) and (S2) was determined. Electrically, we observed an upturned region of resistance at low temperature, and this recovery of the resistance is significantly influenced by the external magnetic field. [ABSTRACT FROM AUTHOR]

In this work, the thermodynamic properties of a Ga1-χAlχAs quantum wire under a parabolic confinement potential, influence of Rashba SOI and presence of Al impurity are studied. External electric and magnetic fields have also been considered. We first formulate the Hamiltonian of the system and then find the eigenenergies, which are used to calculate the partition function. The partition function is the basis of formulating the thermodynamic properties under consideration, viz. mean energy, heat capacity, free energy, entropy and magnetocaloric effect, which are plotted against temperature and impurity. The results show that the mean energy rises with temperature, a peak structure is observed in the heat capacity and the magnetocaloric effect, the free energy steadily decreases with temperature, and the entropy first increases, and then converges to a constant value. The mean energy, heat capacity and free energy increase with impurity, whereas the magnetocaloric effect decreases. The behaviour of all the properties with respect to impurity reverses when the value of impurity becomes greater than ~ 0.6. [ABSTRACT FROM AUTHOR]

This study used the traditional solid-phase reaction method to prepare polycrystalline samples: La0.65Ca0.35Mn1-xNixO3 (x = 0, x = 0.2). The effects of Ni doping on the preformed cluster phases, magnetocaloric effects, and critical behavior were systematically investigated. The results showed that the prepared polycrystalline samples all had cubic chalcogenide structures. The substitution of Ni2+ ions for a certain number of Mn3+ ions reduced the changes in the lattice parameters, unit cell volume, Curie temperature (TC), magnetic entropy, and magnetic entropy change. The changes in these properties originated from the partial substitution of Ni2+ for Mn3+ ions, which changed the Mn3+/Mn4+ ratio and decreased the Mn-O-Mn bond angle, thus weakening the double exchange interaction. Both samples had a preformed cluster phase above the low-temperature magnetic transition temperature. The critical behaviors of both samples fit the tricritical model well. A transition from first- to second-order phase transition existed for both the parent and doped samples, and the maximum magnetic entropy changes of the samples at an applied magnetic field of 7 T were 7.70 and 2.08 J·kg−1·K−1, respectively. [ABSTRACT FROM AUTHOR]

The influence of potassium (K) doping on the magnetic and magnetocaloric effect of the perovskite-type manganese oxides La0.6Sr0.4−xKxMnO3 in low magnetic field has been investigated. Our work shows that the maximum magnetization and the Curie temperature of La0.6Sr0.4−xKxMnO3 (x = 0.10, 0.15, 0.20) decrease with increasing K content. Using Hamad's phenomenological model, we have estimated the important magnetocaloric properties such as the magnetic entropy change and the relative cooling power. Tunable Curie temperature and considerable magnetocaloric properties of these manganese oxides are advantageous for applications in sub-room and near-room temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect-(MCE) of MgB2 is simulated, considering the effect of sintering temperature on MCE. The results show that MCE of MgB2 samples is an inverse type in a temperature range of diamagnetic-paramagnetic transition. Moreover, the MCE for MgB2 is improved with high sintering temperature. The comparison between MCE of MgB2 samples and other some reported magnetic materials has been done, showing that MCE parameters of MgB2 samples are larger than some MCE parameters of La1-xCdxMnO3, La1.25Sr0.75MnCoO6, Gd1−xCaxBaCo2O5.5, Ni58Fe26Ga28, Ni2+xMn1−xGe, Ge0.95Mn0.05 film, and (001)-oriented MnAs film. It suggested that MgB2 samples could be a promising sharing candidate for MR in cryogenic temperatures. [ABSTRACT FROM AUTHOR]

The structural, magnetic and magnetocaloric effect (MCE) properties were studied in DyCoO3 nanoparticles. The synthesized DyCoO3 nanoparticles were approximately 200 nm in size with a typical orthogonal perovskite structure. DyCoO3 possesses an antiferromagnetic ordering at TN = 3.9 K. In magnetic field changes of 0–60 kOe, a giant maximum magnetic entropy change of 16.6 J/kg K and a relative cooling power of 354 J/kg were obtained around TN. These results suggest that DyCoO3 nanoparticles could be regarded as promising candidate for low temperature magnetic refrigerants. [ABSTRACT FROM AUTHOR]

In this work, we consider a quantum dot in the presence of electric and magnetic fields simultaneously. Given the importance of studying the magnetocaloric effect (MCE), we have tried to investigate MCE in this system and obtain the influence of system parameters on the MCE. For this purpose, we obtained the energy levels and eigenstates analytically. Our purpose is to study the effects of temperature and electric field on the entropy change ( Δ S ). To this end, we have employed the non-extensive thermodynamic to study the MCE. We have found that the non-extensive parameter, quantum dot radius and the electric field are important factors to control the MCE. The obtained results also show that our system presents the direct MCE. Also, by applying the non-extensive thermodynamics, we cannot see the oscillating MCE at low temperatures. [ABSTRACT FROM AUTHOR]

In this research work, samples of Pr0.8Sr0.2MnO3 were prepared using two methods: the conventional high-temperature ceramic method (sample R1) and the sol–gel method (sample R2) in order to form a composite. The Curie temperatures were found to be 161 K and 210 K for R1 and R2, respectively. We conducted a theoretical investigation of the magnetic and magnetocaloric (MC) properties of a composite constructed from R1 and R2 compounds to enhance the MC effect.The results suggest that our composite, with a Curie temperature evaluated at 190 K, could be a potential candidate for magnetic refrigeration. Refined values of the critical exponents β, γ, and δ, determined from the modified Arrott plots and the Kouvel–Fisher method, indicate that the behavior of the composite compound is consistent with the 3D Heisenberg model for T ≤ TC and with the mean-field model for T > TC. [ABSTRACT FROM AUTHOR]

The magnetic refrigerator (MR) has gained popularity due to its potential to improve the energy efficiency of refrigeration without the use of unsafe gas, as is the case with traditional gas compression techniques. Magnetocaloric lanthanum manganite investigation, particularly at room and cryogenic temperatures, shows favorable results for the development of MR. Previous thermodynamic models require a significant amount of time and effort to estimate the magnetocaloric effect (MCE). Consequently, we employ the phenomenological model (PM), which is simple and straightforward, requiring fewer parameters than many other modeling methods. We studied the magnetocaloric effect (MCE) of silica-coated La0.54Sr0.27Gd0.19MnO3 (LSGMO) nanoparticles via PM. According to PM results, MCE parameters were obtained as the consequences of the simulated magnetization of silica-coated LSGMO nanoparticles vs. temperature under 0.1 T a magnetic field. It is revealed that the MCE of silica-coated LSGMO nanoparticles covers a broad range of temperatures between 200 and 330 K. The comparison of MCE parameters for silica-coated LSGMO nanoparticles and some published works shows that silica-coated LSGMO nanoparticles are considerably larger than some of the MCE parameters in these published works. Finally, silica-coated LSGMO nanoparticles are suitable function materials in MR, especially at room and cryogenic temperatures, contributing to efficient MR. [ABSTRACT FROM AUTHOR]

This study modeled and investigated the magnetocaloric effect in Ni2MnGa Heusler alloy characterized by its magnetic entropy change (ΔSm) and its refrigerant capacity (RCFWHM) by using the effective field theory. It was found that the peak of the negative magnetic entropy change (ΔSmpk) and the RCFWHM decreased as the external magnetic field increased, whereas the full width half maximum peak (δTFWHM) and the temperature (Tpk) of the ΔSmpk both increased. At higher external magnetic fields, δTFWHM and Tpk were close to each other, but the ΔSmpk and RCFWHM were separated from each other. The RCFWHM of the corner atoms (Ni1 and Ni3) was higher than those of the central atom (Ni5). This result revealed that corner atoms have an important role in the magnetocaloric properties of Ni2MnGa and other materials with a magnetocaloric effect. [ABSTRACT FROM AUTHOR]

We studied some magnetic behaviors of the Ising model in a triangular spin tube using the effective field theory (EFT) with correlations. We examined the effects of the exchange anisotropy J ′ = J ⊥ J / / , and temperature T on the magnetic properties of the spin ½ Ising model in a triangular spin tube, particularly for isotherm magnetization, spontaneous magnetization, and magnetic susceptibility. We investigated the magnetic properties of the triangular spin ½ tube in detail. At low temperature, magnetization curves of a triangular spin ½ tube of the Ising model with the intra- triangular J┴, and inter-triangular J// interaction exchange are examined within the behavior magnetic. It is shown that the developed model satisfactorily describes all pronounced features of the low-temperature magnetization process and the magneto-thermodynamics such as abrupt changes of the isothermal magnetization curves, a giant magnetocaloric effect. Among the most notable features of zero-temperature magnetization curves, one could mention fractional magnetization plateaus, quantum spin liquids, and macroscopic magnetization jumps, which can be found first of all in frustrated quantum Heisenberg spin models. [ABSTRACT FROM AUTHOR]

In this work, we used the mean-field theory (MFT) to estimate the spontaneous magnetization Mspont(T) from the dependence of magnetic entropy change on magnetization, - Δ S M vs. M2 in Gd3Ni2 and Gd3CoNi systems. The obtained Mspont(T) values are in good agreement with those found from the classical extrapolation from the Arrott plots (H/M vs. M2), confirming that the MFT is a valid approach to estimate the spontaneous magnetization. An excellent agreement has been found between the - Δ S M values estimated by Landau theory and those obtained using the classical Maxwell relation. [ABSTRACT FROM AUTHOR]

A phenomenological model (PM) is applied to simulate the magnetocaloric (MC) effect of iron oxide nanoparticles (IONs). Based on modeling results, MC parameters of IONs are deduced as the consequences of simulation for magnetization vs. temperature under 1 T magnetic field. There is a remarkable value of full-width at half-maximum of 213 K, giving an important practice for functioning IONs in the magnetic refrigerator (MR). Since IONs can be functioned over a large temperature range as an effective material for MR, covering a substantial and important range of temperatures, including room temperature and cryogenic temperatures. It is concluded that IONs can function as an auspicious MC magnet for the MR; especially IONs have tiny eddy current and hysteresis loss. [ABSTRACT FROM AUTHOR]

In this work, a theoretical description of the second-order magnetic transition as well as the magnetic entropy change of La0.65Ce0.05Sr0.3Mn1−xCuxO3 (x = 0 and x = 0.15) compounds is presented based on the Bean–Rodbell model of magneto–volume interactions. It is shown that the magnetocaloric properties obtained from initial magnetization isotherms data are in a good matching with the numerical simulations. Within the framework of this specific theoretical model, the magnitude of the spin–lattice interactions as well as the spin value fluctuation are found to increase upon Cu-doping. These observations shall be taken in accordance with the disorder induced by Cu2+/Cu3+ ions in the system. To give a better grasp of magnetic transition and the total entropy change, we figured out the link of lattice/electronic energy contribution to the effective magnetic entropy change from Bean–Rodbell model. [ABSTRACT FROM AUTHOR]

A phenomenological model (PM) is applied to simulate magnetocaloric effect (MCE) of YbFe2As2 (YFA) sample. Based on PM, MCE parameters are deduced as the results of simulation for magnetization versus temperature under 5 T magnetic field. The maximum value of magnetic entropy change is 2.55 J/kg K. The values of full-width at half-maximum relative cooling power and refrigerant capacity are 34 K, 87 J/kg, and 62.6 J/kg, respectively. It is recommended that YFA can be used as an effective material of magnetic refrigerator over a temperature range, covering a significant range of temperature between 0 and 50 K. This indicates that YFA is considered as the MCE material functioning at a liquid helium temperature zone. [ABSTRACT FROM AUTHOR]

A series of Gd1−xHoxMnO3 (x = 0, 0.1 and 0.2) compounds known to exhibit multiferroic properties has been investigated for their structural, magnetic and magnetocaloric properties. X-ray diffraction analysis confirms the presence of single orthorhombic phase at room temperature in all the compositions. Low temperature magnetocaloric properties of these compounds have been studied through specific heat measurements in the temperature range of 0–80 K under different magnetic fields of 0, 2 and 5 T. These studies also revealed the existence of Mn3+ ordering transition and lock-in transition (Tlock) near 40 K and 20 K, respectively. These compounds displayed antiferromagnetic (AFM) ordering of Gd3+ ions at low temperatures below 10 K. The magnetocaloric effect has been quantified in terms of the magnetic entropy change (ΔS)M and adiabatic temperature change (ΔT)ad in the vicinity of AFM transitions. [ABSTRACT FROM AUTHOR]

In this work, an overview of the Weiss molecular mean-field theory, the Bean–Rodbell model and the Landau theory is presented, providing the theoretical background for simulating the magnetocaloric properties for La0.6Ca0.2Na0.2MnO3 manganite. Results showed that sample exhibits second-order ferromagnetic (FM)–paramagnetic (PM) magnetic phase transition and relatively higher values of magnetic entropy change (−∆SM). In application point of view, this material can be used in magnetic refrigeration technology. The theoretical values of −∆SM determined using each theory agree well with the experimental ones estimated from Maxwell relations. In other part, a good agreement in the spontaneous magnetization values, Mspont(T), estimated from (−∆SM vs. M2) and (H/M vs. M2) data was found. Also, the values of the critical exponent (β) found from both methods are close and check that the mean-field model is adequate to study the MCE in La0.6Ca0.2Na0.2MnO3 sample. [ABSTRACT FROM AUTHOR]

In this work, low-temperature magnetic properties and magnetocaloric properties of Fe91−xZr9Cux (x = 0.0, 0.4 and 1.0) amorphous ribbons were investigated. It was found that the Curie temperature (TC) of the ribbons increases with Cu content from 210 (for x = 0) to 218 K (for x = 0.4), and decreases to 214 K with the further of 1.0% Cu. The values of the maximum magnetic entropy change (− ΔSM)max were found to be 2.63, 2.75 and 2.88 J kg−1 K−1 for the Fe91−xZr9Cux (x = 0.0, 0.4 and 1.0) amorphous ribbons, respectively, under the field of 50 kOe. The corresponding refrigeration capacity (RC) values of the Fe91−xZr9Cux (x = 0.0, 0.4 and 1.0) amorphous ribbons are 114, 121 and 120 J kg−1, respectively. These values are comparable to those obtained for the previously studied ternary Fe-based amorphous alloys. These results demonstrate that an appropriate amount of Cu substitution can enhance the (− ΔSM)max and RC of Fe-based amorphous alloys. These Fe-based amorphous alloys are promising for application as low-temperature magnetic refrigerants and multi-functional materials. [ABSTRACT FROM AUTHOR]

The Nd0.6Sr0.4MnO3 sample has been synthesized by the solid-state reaction. In this research paper, structural, morphological, magnetic and magnetocaloric properties are reported. The refinement by Fullprof has revealed the coexistence of both Pnma orthorhombic and R-3c rhombohedral phases. The obtained magnetic results show a paramagnetic–ferromagnetic transition at TC = 245 K. The magnetocaloric effect was estimated from the magnetic isotherms. We can estimate that the magnetic entropy change (ΔS) values by the Hamad theory are very close to those obtained using the classical Maxwell relation. Under an applied field 5 T, the maximum of the magnetic entropy change (ΔS) max and the relative cooling power is found to be 3.68 J/kg K and 216.03 J/kg, respectively. The obtained values are compared with those of some other reported manganite and show that our compound could be a promising candidate for magnetic refrigeration. Finally, the construction of the universal curve of the magnetic entropy change confirmed the studied manganite undergoes a second-order magnetic phase transition. [ABSTRACT FROM AUTHOR]

In the current research work, a phenomenological model is applied to describe the magnetocaloric effect (MCE) of the two phases 0.75 La0.6Ca0.4MnO3/0.25 La0.6Sr0.4MnO3 composite system. Based on this model, the values of the magnetocaloric properties are predicted from the calculation of magnetization as a function of temperature under different external magnetic fields. A significant MCE is obtained over a large range of temperature compared to those observed in the mother compounds, La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3, making of this material considered as a promising candidate for magnetic refrigeration applications in moderate magnetic fields near room temperature. The results are then compared to those obtained experimentally in our previous work. The excellent agreement observed between both data proves the validity of the adopted model in the estimation of the MCE properties of material under investigation. [ABSTRACT FROM AUTHOR]

The crystal structure, magnetic and magnetocaloric properties of the binary NdPd compound were investigated by X-ray diffraction and the physical property measurement system in detail. The NdPd compound with a CrB structure exhibits a second-order magnetic phase transition from ferromagnetic to paramagnetic states at the Curie temperature TC = 15.5 K. For a magnetic field change of 0–5 T, the peak value of magnetic entropy change (− ΔSM) is evaluated to be 12.2 J/kg K, and the corresponding refrigerant capacity (RC) reaches its maximal value of 94 J/kg. The relatively small thermal hysteresis and magnetic hysteresis with the considerable magnetocaloric effect indicate that NdPd is an anticipated material for the low-temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

In the present work, we aim to analyze the magnetocaloric and electrical properties of (La0.75Nd0.25)2/3(Ca0.8Sr0.2)1/3MnO3 manganite prepared by solid-state method at high temperature. The experimental results of the magnetization show that the (La0.75Nd0.25)2/3(Ca0.8Sr0.2)1/3MnO3 compound exhibits a paramagnetic–ferromagnetic transition at TC = 240 K. In addition to the experimental study, theoretical approaches are adopted to investigate the magnetocaloric behavior of this sample. The important parameters such as maximum entropy change, full width at half maximum (δTFWHM) and relative cooling power are explained qualitatively. The electrical properties of the studied sample have been investigated by using a complex impedance spectroscopy technique. These electrical measurements reveal that (La0.75Nd0.25)2/3(Ca0.8Sr0.2)1/3MnO3 sample exhibits a metallic behavior at low temperature and insulator one at high temperature. The temperature (TMI) of the metal–insulator transition is found to be about 240 K. The effects of frequency, temperature and composition on permittivity ε′, ε″ and dielectric loss (tanδ) have been also discussed in terms of hopping of charge carriers between Mn3+ and Mn4+ ions. [ABSTRACT FROM AUTHOR]

In this study, the critical behavior and magnetic and magnetocaloric properties in a polycrystalline Pr0.8Sr0.2MnO3 sample synthesized by solid-state technique were investigated in detail. By analyzing the temperature and the field dependence of magnetization, we have demonstrated that this compound exhibits a clear second-order magnetic phase transition around the Curie temperature estimated at TC = 161 K. Refined values of the critical exponents β, γ and δ determined by the modified Arrott plots, the critical isotherm and Kouvel–Fisher analysis show that our compound is described by the 3D Ising model. The reliability of these critical exponents was further confirmed using the universal scaling hypothesis. Under an applied magnetic field of 5 T, the calculated value of the maximum of the magnetic entropy change is estimated at 1.740 J K−1 kg−1 and the relative cooling power (RCP) turns out to be 134.46 J kg−1. Moreover, the critical exponents were evaluated from RCP results which confirm the correlation between the critical behavior and magnetocaloric results in the Pr0.8Sr0.2MnO3 compound. [ABSTRACT FROM AUTHOR]

The influences of Mn/Fe ratio on the structural, magnetic and magnetocaloric properties of Gd6(Mn1−xFex)23 (x = 0.0–0.5) compounds have been investigated by means of X-ray diffraction (XRD) and magnetic measurements. The XRD results show the compounds crystallize in the cubic Th6Mn23-type structure, and the lattice size decreases with the decrease in Mn/Fe ratio. Magnetic measurements show that the samples exhibit a second-order magnetic transition from TC = 99 K for x = 0.3 down to TC = 89 K for x = 0.4 and increase to 293 K for x = 0.5. The magnetization measured at 10 K decreases from 119 emu/g for x = 0.0 to 82 emu/g for x = 0.4, but the magnetization is 105 emu/g at x = 0.5. For an applied field from 0 to 5 T, the maximum values of magnetic entropy change (− ΔSM) for Gd6(Mn1−xFex)23 compounds with x = 0.3, 0.4 and 0.5 are 3.56 J/kg K, 3.77 J/kg K and 1.79 J/kg K, respectively. The properties of Gd6(Mn1−xFex)23 compounds help to understand the exceptional physical characteristics and provide the information for seeking giant magnetocaloric materials. [ABSTRACT FROM AUTHOR]

The composite $$(\hbox {La}_{0.67}\hbox {Ca}_{0.33}\hbox {MnO}_{3})/\hbox {La}_{0.7}\hbox {Ba}_{0.3}\hbox {MnO}_{3})$$ sample was prepared using the conventional solid-state reaction method, and their crystallographic structure was achieved by X-ray diffraction pattern analysis. The magnetic and magnetocaloric effect has been studied by magnetization measurements. Based on the relation: $$\chi ^{-1}(T)\propto (T-T_\mathrm{C}^\mathrm{Rand} )^{1-\lambda }$$ , the inverse of susceptibility shows a downturn before $$T_\mathrm{C }$$ indicating the existence of Griffiths phase for the temperature range $$T_\mathrm{C}^\mathrm{Rand}

Magnetic properties of CeFeSi-type NdMn $$_{1-x}$$ Ti $$_{x}$$ Ge compounds studied by magnetization and magnetocaloric measurements are reported. The increase in Ti content leads to the essential increase in magnetic ordering temperature of the Nd sublattice and the magnetocaloric effect. The results are compared with those obtained on isotypic RTX compounds and discussed assuming the itinerant character of magnetism of these compounds. [ABSTRACT FROM AUTHOR]

The thermodynamic behavior of the spin $$S=1/2$$ antiferromagnetic two-leg ladder compound (C $$_5$$ H $$_{12}$$ N) $$_{2}$$ CuBr $$_{4}$$ in a uniform magnetic field is studied using numerical and analytical approaches. The entropy $$S(H,T)$$ and specific heat $$C(H,T)$$ are calculated. The specific heat shows various behaviors in different regions of the magnetic field. The field dependence of the specific heat is almost symmetric about the average of quantum critical fields in complete agreement with experimental results. In addition, it is found that during an adiabatic demagnetization process, temperature drops in the vicinity of the field induced zero-temperature quantum phase transitions. [ABSTRACT FROM AUTHOR]

We report low-temperature magnetization measurements on a copper-containing coordination polymer [Cu( μ-C2O4)(4-aminopyridine)2(H2O)] n. According to these measurements and previous results (Prokofiev et al. in Cryst. Res. Technol. 42, 394, ), the material is a very good realization of an S=1/2 antiferromagnetic Heisenberg chain with a small saturation field B s=4.2 T, which marks the endpoint of a quantum-critical line in the B– T plane. Measurements of the magnetocaloric effect at low temperatures T=0.47 K across the saturation field yields a very large magnetothermal response with a characteristic sign change close to the quantum-critical point. The data are in good agreement with the quantum-critical behavior calculated on the basis of exact diagonalization and quantum Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

We report magnetic and magnetocaloric properties of the polycrystalline series of Dy1− xGd x(Co1− xNi x)2 ( x=0.1, 0.2, 0.3, 0.4 and 0.5) solid solutions. The samples were characterized by powder X-ray diffraction patterns taken at room temperature and revealed that all the Dy1− xGd x(Co1− xNi x)2 solid solutions consist of the C15 cubic Laves phase MgCu2 type structure and a small amount of DyCo3 and Dy2O3 impurity phases. Magnetic measurements showed that the samples undergoes a second-order type phase transition at TC<130 K, from paramagnetic to ferromagnetic state. Heat capacity measurements have been performed for all solid solutions and allowed us to determine the Debye temperature. The magnetocaloric effect has been studied by means of specific heat measurements in magnetic field 0.42, 1 and 2 T. The GdNi2 substitution effect on magnetic and magnetocaloric properties will be discussed. [ABSTRACT FROM AUTHOR]