Study Of Magnetocaloric Effect Research Articles

Strongly anisotropic magnetocaloric effect in a dipolar magnet LiGdF4

We report the detailed study of the magnetocaloric effect (MCE) in a dipolar-Heisenberg magnet LiGdF4 using magnetization measurements performed on a single crystal sample. Entropy variation on isothermal demagnetization from the magnetic field up to 3 T is determined in the temperature range 2–10 K for two principal directions of the applied field (parallel and perpendicular to the tetragonal c-axis of the crystal). The MCE is found to be highly anisotropic, with the cooling efficiency being up to twice higher at H∥c. The results are nicely interpreted in the frame of a conventional molecular field approach taking into account considerable anisotropy of the paramagnetic Curie–Weiss temperature. These results are compared to earlier studies of MCE in powder samples of LiGdF4 (Numazawa et al., 2006) as well as with analogous data for other well known magnetocaloric materials. Our findings may open new possibilities to enhance the efficiency of magnetic refrigeration in the liquid helium-4 temperature range.

Monte Carlo study of magnetocaloric effect and magnetic properties of the nano- borophene bilayer with RKKY exchange interactions of a mixed spin 2 and 3/2

In this study, we have studied the magnetic properties and magnetocaloric effect of the nano-borophene bilayer with RKKY (Ruderman-Kittel-Kasuya-Yosida) exchange interactions of mixed spin 2 and 3/2 using Monte Carlo calculations. In the first part of this investigation, the ground state phase diagrams for zero temperature are reported and discussed. We also determined the critical temperature for varying the number of non-magnetic layers (NML) and the interacting couplings Jss. In the second part, we investigated the influence of the parameter NML, the exchange couplings Jss and Jσσ, and the crystal field on the total magnetizations and the magnetic hysteresis loop. The specific heat and magnetic entropy changes versus of the temperature under the effect of different external magnetic fields and the parameter Jss. Finally, we analyzed the relative cooling power (RCP) for distinct external magnetic field and Jss.

Magnetic and magnetocaloric properties of polycrystalline Pr[formula omitted]Ca[formula omitted]MnO[formula omitted] (x [formula omitted] 0.85, 0.90, 0.95) compounds: Emergence of large inverse and conventional magnetocaloric effects

Magnetic and magnetocaloric effect have been investigated for the electron doped polycrystalline Pr1−xCaxMnO3 (x ∼ 0.85, 0.90, 0.95) compounds. The experimental outcomes indicate that the nature of the ground state is very much sensitive with the doping concentration. Pr0.15Ca0.85MnO3 compound exhibits antiferromagnetic ground state. In contrast to that ferromagnetic nature was found for the Pr0.10Ca0.90MnO3 and Pr0.05Ca0.95MnO3 compounds. Although, for x∼0.90 ferromagnetic phase was stable. However for x∼ 0.95, the ferromagnetic state is quite unstable. Additionally for the doping concentration x∼ 0.95, the anomalous nature was found in temperature dependent coercivity. Magnetocaloric effect study indicate that antiferromagnetic Pr0.15Ca0.85MnO3 compound exhibits large inverse magnetocaloric effect (10.5 J/kg-K at H = 70 kOe magnetic field). On the other hand, ferromagnetic Pr0.10Ca0.90MnO3 and Pr0.05Ca0.95MnO3 compounds show conventional magnetocaloric effect. The magnetocaloric entropy change for x∼0.90 compound is significantly large (7.5 J/kg-K at H = 70 kOe magnetic field) and comparable with the other reported magnetic refrigerant materials. Universal master curve for magnetic entropy change have been constructed for all the materials having inverse and conventional magnetocaloric effect by proper scaling of temperature axis.

Systematic studies of the magnetocaloric properties for the La0.65Ca0.25A0.1MnO3 series (A = alkali metal and alkaline earth metals)

We present results of systematic studies of magnetocaloric effect (MCE) in a series of manganites La0.65Ca0.25A0.1MnO3 with Ca substituted by alkali metal (A = Li, Na, K, Rb, Cs) and alkaline earth metals (A = Mg, Ca, Sr, Ba), i.e. by s-block elements. At first stage we studied La1-xCaxMnO3 for × in the range 0.35–0.4 and we found that the La0.65Ca0.35MnO3 compound was the best starting composition for further fine-tuning the MCE properties by substitution for Ca with A. For each of the La0.65Ca0.25A0.1MnO3 samples an extensive characterization of the physical properties was carried out, including: structural analysis, magnetic susceptibility and magnetization vs applied magnetic field measurements, magnetic phase transition identification by Arrott plots, and finally determination of the isothermal magnetic entropy change −ΔSM. The obtained results indicate a path for searching a compromise composition, i.e. a material exhibiting a reasonable MCE performance at temperatures close to room temperature.

Magnetocaloric Effect in Half-Doped and Self-Doped Manganites: A Study to Green Refrigeration

Magnetic refrigeration has emerged as a promising and environmentally friendly technology due to its high efficiency and eco-friendly nature. It is becoming a strong competitor to traditional gas refrigeration and is often referred to as a green refrigeration technique. This technique utilizes the magnetocaloric effect (MCE) or inverse magnetocaloric effect (IMCE) to achieve a change in temperature after adiabatic demagnetization. Among various magnetocaloric materials, perovskite manganites have drawn significant attention due to their abundance and low field MCE. In this paper, a comparative study of MCE has been presented for two different types of manganites. The self-doped La0.9MnO3 shows a considerable amount of MCE (2.5 J/Kg-K) at an applied magnetic field of 10 kOe around 255 K. In contrast, Pr0.5Sr0.5Mn0.98Cr0.02O3another manganite, shows a comparably lower value of MCE (0.55 J/Kg-K) around 220 K under the same magnetic field, but it exhibits a large IMCE (1.26 J/Kg-K) around 150 K. This comparative study provides insights into the magnetocaloric properties of these manganites, which could have potential applications in green refrigeration.

Quantum description of magnetocaloric effect, thermo-magnetic properties and energy spectra of LiH, TiH, and ScH diatomic molecules under the influence of magnetic and Aharonov-Bohm (AB) flux fields with Deng-Fan-Screened Coulomb potential model

Quantum description of the isothermal and adiabatic magnetocaloric effect (MCE), thermomagnetic properties, and energy spectra of three diatomic molecules, namely: lithium hydride (LiH), titanium hydride (TiH), and scandium hydride (ScH), was examined with Deng-Fan-Screened Coulomb Potential using the Greene-Aldrich approximation to the centrifugal term. The numerical solutions of the proposed potential with and without the magnetic and AB flux fields obtained reveal that the combined impacts of the magnetic and AB flux fields completely remove the degeneracy of the energy spectra and control the behaviour of the MCE by acting as a regulating factor to cool or heat the MCE. Also, the proposed potential reduces to three exceptional cases, and the thermomagnetic plots obtained for the analysed dimer molecules agreed perfectly with previous work. This research has the potential to be applied in molecular physics and MCE studies for a variety of molecules.

Study of magnetocaloric effect and magnetic properties of the nano-graphene bilayer with RKKY interactions of a mixed spins S = 3/2 and σ = 3: a Monte Carlo simulation

Study of magnetocaloric effect and magnetic properties of the nano-graphene bilayer with RKKY interactions of a mixed spins S = 3/2 and σ = 3: a Monte Carlo simulation

Recent progress in the development of RE2TMTM’O6 double perovskite oxides for cryogenic magnetic refrigeration

• The research progress of MCE in RE 2 TMTM ’O 6 DP oxides is reviewed • The magnetism, MTP and magnetocaloric performances are summarized. • Some of the Gd 2 TMTM ’O 6 DP oxides are considerable for cryogenic MR. The magnetic functional materials play a particularly important role in our modern society and daily life. The magnetocaloric effect (MCE) is at the basis of a solid state magnetic refrigeration (MR) technology which may enhance the efficiency of cooling systems, both for room temperature and cryogenic applications. Despite numerous experimental and theoretical MCE studies, commercial MR systems are still at developing stage. Designing magnetic solids with outstanding magnetocaloric performances remains therefore a most urgent task. Herein, recent progresses on characterizing the crystal structure, magnetic properties and cryogenic MCE of rare earths ( RE )-based RE 2 TMTM ’O 6 double perovskite (DP) oxides, where TM and TM ’ are different 3d transition metals, are summarized. Some Gd-based DP oxides are found to exhibit promising cryogenic magnetocaloric performances which make them attractive for active MR applications.

Semiconducting nature, magnetic critical exponent, and magnetocaloric effect study near room temperature on Fe[sbnd]Mn[sbnd]Al alloy

The Fe2.5Mn0.5Al Heusler alloy, prepared by Arc melting method, crystallizes to B2 in the Fm-3m space group. Resistivity measurement shows semi-metallic behavior in low temperature due to the dominance of magnon-magnon scattering and, exhibits semiconducting nature above the Curie temperature. Hence, it is predicted that there is a correlation between magnetic ordering and electrical transport properties. Arrott plot, Kouvel fisher method, and Widom scaling relation have been used here to determine the critical exponents. The Curie temperature (TC) is found to be near room temperature at 280 K. Also, critical exponents indicate that the magnetic ordering is following mean-field theory i.e., long-range interaction is present with 2nd order para to ferromagnetic transition. On the other hand, due to the 2nd order magnetic phase transition, significant magnetocaloric effect has been observed in a wide temperature range near room temperature. The maximum entropy change is found at 280 K i.e., at Tc.

Re-entrant Spin Glass and Magnetocaloric Effect in Frustrated Double Perovskite Ho2CoMnO6 Flat Nanorod

In the present work, we have synthesized single-phase flat nanorods of double perovskite Ho2CoMnO6 (HCMO) by following a hydrothermal route. The sample crystallizes into a monoclinic structure with a P21/n space group. Expansion of MnO6 octahedra and hence increase in unit cell volume as compared to its bulk counterpart is observed. Unlike the single ferromagnetic transition in the bulk HCMO sample, here magnetization versus temperature measurements show three magnetic transitions corresponding to ferromagnetic (FM), antiferromagnetic (AFM) and re-entrant spin glass (SG) ordering at 182, 97 and 31 K respectively. The FM transition (Tc) which is much higher than the bulk is attributed to super-exchange interaction in Co2+- O - Mn4+ networks and the AFM transition is due to exchange interactions across Co2+- O – Co2+ and Mn4+- O - Mn4+ networks, as well as due to the presence of Co3+ and Mn3+ ions, which is proven by the XPS analysis. The glassy magnetic phase is confirmed by magnetic relaxation and aging effect studies. A low value of coercivity (Hc) and saturation magnetization (MS) is observed for HCMO flat nanorods (8.52 µB/f.u) as compared to that of bulk HCMO (14.9 µB/f.u). It may be due to the presence of higher oxidation states of ions as well as the introduction of AFM ordering and frustration in the system. A study of magnetocaloric effect gives a change in entropy value of 12.4 J/K.Kg at low temperature for 7 T.

Influence of phase boundary on magnetic and magnetocaloric properties of nanocrystalline La0.17Ca0.83MnO[formula omitted] sample

In this present study we report the Magnetic properties and magnetocaloric effect of two nanocrystalline La0.17Ca0.83MnO3 samples with average particle size ∼40 nm and ∼70 nm. According to the reported phase diagram, the bulk compound lies near the phase boundary between charge ordered antiferromagnetic and canted antiferromagnetic state. In contrast to the bulk counterpart, the significant effect of the phase boundary was observed on the physical properties of nanocrystalline compounds. Moreover, the signature of canted magnetic phase in nanocrystalline sample was probed through magnetocaloric effect study.

Magnetocaloric effect in La0.70Ag0.25MnO[formula omitted] magnetic nanoparticles

Experimental study of magnetocaloric effect (MCE) was performed by direct and indirect methods on La0.70Ag0.25MnO3+δ nanoparticles with rhombohedral LaAlO3 – type crystal structure (R3¯c space group – No. 167, hP30). The content of oxygen was modified by annealing at 800 °C/48h in different atmosphere (air, O2 and Ar). The Curie temperature TC increases from 250 K to 319.5 K and to 322.9 K with the content of oxygen. The adiabatic temperature change ΔT(4T) = 1.52 K, the change of magnetic entropy −ΔSmax(4T) = 3.96 Jkg−1K−1 and the relative cooling power RCT(4T) = 172 J/kg are maximal for sample treated in Ar and decrease with oxygen content. The frequency dependence of ΔT (f) and the shape of maximum in ΔT (T) and −ΔSmax (T) indicate relaxation processes and presence of magnetic inhomogeneities which are present mostly in sample treated in Ar. The samples demonstrate the stability of the MCE up to 1000 cycles of switching on and off the magnetic field without any signs of degradation.

Magnetocaloric properties of a ribbon sample of Heusler alloy Ni-=SUB=-45-=/SUB=-Co-=SUB=-5-=/SUB=-Mn-=SUB=-31-=/SUB=-Al-=SUB=-19-=/SUB=-: experimental and theoretical studies

The results of experimental and theoretical studies of magnetocaloric properties of a ribbon sample of alloy Ni45Co5Mn31Al19 in the range of T=80-350 K in magnetic fields of up to 8 T are given. This alloy demonstrates a first-order magnetostructural phase transition (MSPT) in the temperature range of 270 K, as well as a second-order transition --- at the Curie temperature of 294 K. The magnetocaloric effect (MCE) was studied both by the direct method of magnetic field modulation in cyclic fields up to 8 T and by the classical extractive method. Field dependence of MCE have a different nature for first- and second-order phase transitions. A reverse MCE near MSPT is irreversible, i.e. the final sample temperature is 0.75 K below the initial one. Theoretical studies of magnetic properties and MCE of the studied sample were performed by ab initio calculations and Monte Carlo modeling. Theoretical temperature dependences of MCE are characterized by a similar interval of effect manifestation in the region of martensitic transformation and a narrower interval in the region of austenite Curie temperature as compared to the experiments, which is conditioned by the presence of a heterogeneous mixed state of austenite in the experimental sample. On the whole, theoretical data qualitatively and quantitatively reproduce the experimental dependences. Keywords: magnetocaloric effect, cyclic fields, Heusler alloy, Monte Carlo method.

Magnetic and magnetocaloric effect study of a polycrystalline Gd0.5Sr0.5-xCaxMnO3 compound.

The magnetic and magnetocaloric properties of polycrystalline Gd0.5Sr0.5-xCaxMnO3 (x = 0.0, 0.2, 0.3, 0.4 and 0.5) compounds have been investigated. Depending upon the Ca and Sr proportions, fascinating magnetic ground states were observed in the Gd0.5Sr0.5-xCaxMnO3 compounds. Here, the dominating nature of the canted magnetic state (for the Gd0.5Ca0.5MnO3 compound) and glassy (disordered ferromagnetic) magnetic state (for the Gd0.5Sr0.5MnO3 compound) are observed. However, for the intermediate doped samples (x = 0.2, 0.3, 0.4), a competing nature is found in their magnetic and exchange bias properties. Additionally, in the low temperature region, a significantly large magnetocaloric effect is observed for all the samples. At a 70 kOe external magnetic field, the highest observed value of the magnetocaloric entropy change is 21.58 J kg-1 K-1 (for the Gd0.5Ca0.5MnO3 sample) and the lowest is 10.15 J kg-1 K-1 (for the Gd0.5Sr0.5MnO3 sample).

Multifunctional properties of Cr-substituted ferromagnetic Nd2Fe17

The detailed X-ray diffraction studies of the structural phase along with its thermal expansion properties have been carried out of the rare-earth based compounds Nd2Fe17-xCrx (x = 0, 0.5, 1.0, and 2.0). They are crystallized in the rhombohedral structure (Th2Zn17 type) with space group R-3m. A very negligible (close to zero) thermal expansion coefficient |α| = 1.9 × 10−6 K−1, was found over a large temperature range 15–320 K in Nd2Fe16.5Cr0.5 compound (TC ~ 366 K) attributable to the diminution of magneto-volume effect. This kind of zero thermal expansion (ZTE) magnetic system has a great practical significance having TC higher than 300 K. The parent compound Nd2Fe17, as a magnetocaloric material, has high relative cooling power (RCP) (625 J kg−1 at μ0H = 0–9 T), elevated operational temperature (326 K) and comparatively high entropy change (|ΔSM|max) at TC. Because of these properties Nd2Fe17 can operate as a promising refrigerating system. The critical behaviour of all the four samples is studied by means of the isotherm magnetization in the vicinity of TC. The critical exponents are evaluated using various methods, for instance, modified Arrott plot, critical isotherm, Kouvel–Fisher plot in addition to the study of magnetocaloric effect. From the critical analysis it is revealed that all the four samples belong to different types of universal magnetic class.

High pressure study of magnetocaloric effect in Ho3Co and Tb3Co

The magnetocaloric effect of intermetallic compounds of Tb3Co and Ho3Co is studied under high pressures up to ∼1 GPa using pressure dependent dc magnetisation and specific heat measurements at ambient conditions. The magnetic entropy change (−ΔSM) obtained from magnetisation data and adiabatic change in temperature (ΔTad) determined from zero-field specific heat and magnetisation data are found to be nearly identical within error limits with those deduced from purely field dependent specific heat experiments. With increasing hydrostatic pressure to ∼1 GPa, the −ΔSM and ΔTad, both show a significant enhancement of about 37% and 13%, respectively for 9 T field change in case of Tb3Co. On the other hand, Ho3Co exhibits a decrease of about 8% in both −ΔSM and ΔTad with increasing pressure. The refrigerant capacity (RC) also increases from 650 J kg−1 to 847 J kg−1 in the case of Tb3Co and it goes down from 665 J kg−1 to 615 J kg−1 for Ho3Co for an increase of pressure to 1 GPa. With increasing pressure, the peak widths of both −ΔSM and ΔTad increase in case of Tb3Co, although the increase is more in −ΔSM. However, such noticeable changes in peak widths with pressure were not observed in Ho3Co. At ambient pressure, peak of −ΔSM () scales with for both the compounds, consistent with the prediction of mean field theory (MFT) for second order magnetic transition. However, deviation from MFT was noticed at high pressures as was found to scale with instead of for both the alloys. Further, normalised −ΔSM curves for different ΔH and pressures collapse on a single universal curve in both the compounds thereby indicating that the second order magnetic transition persists even up to ∼1 GPa pressure.

Study of magnetocaloric effect and critical exponents in polycrystalline La0.4Pr0.3Ba0.3MnO3 compound

Magnetic and magnetocaloric effects of the polycrystalline La0.4Pr0.3Ba0.3MnO3 (LPBMO) compound were extensively studied. The critical parameters were extracted from the magnetic isotherms data near the paramagnetic–ferromagnetic phase transition region. The values of the critical exponents were compared with the standard theoretically predicted universality classes of magnetism. Interestingly, the critical parameters exhibit anomalous nature compared to the standard models. Such a discrepancy was analyzed considering the effect of disorder present in the studied compound. Moreover, the material shows moderate values of the relative cooling power and refrigerant capacity. Additionally, we have also calculated the temperature-averaged entropy change and normalized refrigerant capacity for the studied LPBMO compound.

An experimental and theoretical study of magnetocaloric effect in Nd0.5Dy0.5FeO3

A significant magnetocaloric effect (MCE) has been revealed in our investigation on polycrystalline Nd0.5Dy0.5FeO3 below 30 K. Observed magnetization of the system at low temperature is 32% higher than the expected average magnetization of NdFeO3 and DyFeO3. Such an enhancement in the magnetization led to a large change in magnetic entropy (10.4 Jkg−1 K−1) at 4 K. The observed entropy change is remarkable considering the higher natural abundance of Nd compared to that of Dy and negligible MCE seen in case of NdFeO3. Theoretical calculations performed using mean-field approximation and Monte Carlo simulations on an Ising type spin model indicate that the high magnetocaloric effect is caused primarily by the ordering of rare-earth ions in C-type antiferromagnetic state in presence of molecular exchange field created by Fe ions.

Investigation of size-dependent magnetic ordering in charge ordered antiferromagnetic nanoparticles via magnetocaloric effect

Abstract We have detected size-dependent modifications in magnetic ordering in charge ordered nanoparticles through the study of magnetocaloric effect. Due to prominent surface induced magnetism in nanoparticles, it is very difficult to probe the magnetic ordering in charge ordered antiferromagnetic nanoparticles from direct magnetization study, especially at lower magnetic fields, though at higher magnetic fields the antiferromagnetic/charge ordered transition can be visualized properly. We show that, at comparatively lower magnetic fields, the magnetocaloric effect provides a sensitive way for the detection of such ordering transitions.

Magnetocaloric effect study by means of theoretical models and spontaneous magnetization determination in Ni0.4Mg0.3Cu0.3Fe2O4 ferrite

The magnetocaloric effect (MCE) of Ni0.4Mg0.3Cu0.3Fe2O4 ferrite was analyzed by different theoretical methods such as mean-field, Bean-Rodbell and Landau theories. Results confirm the second order type of the ferromagnetic (FM)—paramagnetic (PM) magnetic phase transition for the sample. The values of magnetic entropy change (−ΔSM) estimated from each theory agree well with those experimentally determined using Maxwell relations. The spontaneous magnetization values (Mspont(T)) determined from both (−ΔSM versus M2) and (H/M versus M2) data are very close, confirming the validity of the magnetic entropy change to estimate Mspont(T) values. The critical exponents (β, γ and δ) obtained for Ni0.4Mg0.3Cu0.3Fe2O4 sample at its Curie temperatures (TC) are close to those predicted in mean-field model.