First-order Magnetic Phase Transition Research Articles

Plastically deformed Gd-X (X = Y, In, Zr, Ga, B) solid solutions for magnetocaloric regenerator of parallel plate geometry

Despite significant progress in the study of materials undergoing first-order magnetic phase transitions accompanied by the so-called giant magnetocaloric effect (MCE), Gd metal still remains the most widely used material in prototypes of magnetic refrigerators due to its significant MCE, good machinability and reasonable mechanical and chemical stabilities. Alloying of Gd enables fine-tuning the Curie temperature of Gd-based solid solutions (all show second-order phase transitions), for graded magnetocaloric materials. Commonly, Gd packed spheres are used as a magnetocaloric working substance in the active magnetic regenerator (AMR) cycle. In this work, we show that the optimized stacking parallel-plate geometry of AMR bed made of Gd is more effective for application at frequencies 1–10 Hz then the packed spheres. We also give a short review on magnetocaloric properties of cold-rolled Gd-X (X = Y, In, Zr, Ga, B) solid solutions. These materials can be produced in the form of thin (∼100 μm) foils/plates to ensure rapid heat exchange between to the heat transfer fluid. Although the magnetocaloric effect decreases in the as-rolled foils, it can be recovered by thermal treatment of the final stacked-plates regenerators. Gd-Y, Gd-In and Gd-Zr solid solutions have magnetocaloric properties, comparable to the MCE of pure Gd in a wide temperature working span up to 37 K, 36 K, and 16 K respectively, which makes them suitable magnetocaloric material systems for testing the fundamental heat exchangers geometries at ambient temperature and in frequencies of 1–10 Hz.

High-temperature phase transition behavior and magnetocaloric effect in a sub-rapidly solidified La–Fe–Si plate produced by centrifugal casting

A sub-rapidly solidified LaFe11.6Si1.4 plate was fabricated directly from liquid by centrifugal casting method. The phase constitution, microstructure and magnetocaloric effect were investigated using backscatter scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and physical property measurement system. When the plate was annealed at 1373K, τ1 phase was formed by a solid-state peritectoid reaction. A first-order magnetic phase transition occurred in the vicinity of 188K, and the effective refrigeration capacities reached 203.5J/kg and 209.7J/kg in plates annealed for 1h and 3h, respectively, under a magnetic field change of 3T. It is suggested that centrifugal casting may become a new approach to prepare high-performance La–Fe–Si magnetocaloric plates for practical applications, which could largely accelerate the formation of τ1 phase during high-temperature heat-treatment process due to refined and homogeneous honeycombed microstructure.

The effect of Co substitution on the magnetic and magnetocaloric properties of Gd3Ru

The effects of Co substitution on the structure, magnetic properties, and magnetocaloric effect of Gd3Ru1−xCox (0.05 ≤ x ≤ 0.20) alloys have been investigated by X-ray diffraction and magnetization measurements. The Curie temperatures varied between 60 K and 92 K with Co substitution for Ru. With an applied magnetic field change (ΔH) of 50 kOe, the maximum values of magnetic entropy change (−ΔSM) were determined to be 25.8, 23.1, 19.4, and 10.8 J/kg K for compositions with x = 0.05, 0.10, 0.15, and 0.20, respectively. The corresponding refrigeration capacities (RCs) for the alloys were reasonably large and calculated to be 495, 475, 467, and 517 J/kg. The magnetic phase transitions in the Gd3Ru1−xCox (0.05 ≤ x ≤ 0.15) alloys are of first-order. In the Gd3Ru0.80Co0.20, the first-order magnetic phase transition disappears and the transition is broadened hence it increases in RC. The high −ΔSM values and accompanying large RCs for the Gd3Ru1−xCox (0.05 ≤ x ≤ 0.20) alloys qualify them as potential candidates for magnetic refrigeration applications near liquid nitrogen temperature.

Transition metal substitution in Fe2P-based MnFe0.95P0.50Si0.50 magnetocaloric compounds

The crystal structure, magnetic and magnetocaloric properties of (Mn,Fe,T)1.95P0.50Si0.50 (T = Co, Ni and Cu) compounds have been investigated. All the compounds crystallize in the Fe2P-type hexagonal structure. All these transition metal substitutions for either Mn(3g) or Fe(3f) weaken the ferromagnetic ordering, while showing complex effects on the energy barrier for nucleation in the first-order magnetic phase transition and result in complex behaviors in thermal/magnetic hysteresis. A first-principles density functional theory calculations show that Co, Ni and Cu atoms occupy 3f, 3f and 3g sites, respectively.

Magnetic field-induced metamagnetism and magnetocaloric effect in double perovskites Re2CoMnO6 (Re=Sm, Dy)

Double perovskites Re2CoMnO6 (Re=Sm, Dy) have been synthesized by a solid-state reaction method. Magnetic field-induced metamagnetic behavior is observed in the samples below the ferromagnetic Curie temperature (TC), which are respectively 123 K and 88 K in Sm2CoMnO6 and Dy2CoMnO6. The origin of this effect is attributed to the competition between the nearest-neighbor ferromagnetic super-exchange interaction (Co2+-Mn4+) and the next nearest-neighbor antiferromagnetic exchange interaction (Co2+-Co2+, Mn4+-Mn4+). Arrott plots combined with the thermal hysteresis confirm that the transition from ferromagnetic to antiferromagnetic state with negative slope is the first-order magnetic phase transition. Moreover, the positive slope closely to TC indicates that the transition from paramagnetic to ferromagnetic state is the second-order transition. Magnetocaloric effect associated with Maxwell's relation is studied and the maximal value of |ΔSM| is 1.4 and 3.5 J kg−1 K−1 at 6 T near TC for Sm2CoMnO6 and Dy2CoMnO6. The large value of |ΔSM| for Dy2CoMnO6 is obtained which is 9.1 J kg−1 K−1 at 20 K. The relatively smaller magneto entropy change for Sm2CoMnO6 may be attributed to the higher coercive field and the weaker magnetism.

Magnetic behavior of metallic kagome lattices, Tb3Ru4Al12 and Er3Ru4Al12

We report the magnetic behavior of two intermetallic-based kagome lattices, Tb3Ru4Al12 and Er3Ru4Al12, crystallizing in the Gd3Ru4Al2-type hexagonal crystal structure, by measurements in the range 1.8–300 K with bulk experimental techniques (ac and dc magnetization, heat capacity, and magnetoresistance). The main finding is that the Tb compound, known to order antiferromagnetically below (TN=) 22 K, shows glassy characteristics at lower temperatures (15 K), thus characterizing this compound as a re-entrant spin-glass. The data reveal that the glassy phase is quite complex and is of a cluster type. Since glassy behavior was not seen for the Gd analog in the past literature, this finding on the Tb compound emphasizes that this kagome family could provide an opportunity to explore the role of higher-order interactions (such as quadrupole) in bringing out magnetic frustration. Additional findings reported here for this compound are: (i) The plots of temperature dependence of magnetic susceptibility and electrical resistivity data in the range 12–20 K, just below TN, are found to be hysteretic leading to a magnetic phase in this intermediate temperature range, mimicking disorder-broadened first-order magnetic phase transitions; (ii) features attributable to an interesting magnetic phase co-existence phenomenon in the isothermal magnetoresistance in zero field, after travelling across metamagnetic transition fields, are observed. With respect to the Er compound, we do not find any evidence for long-range magnetic ordering down to 2 K, but this compound appears to be on the verge of magnetic order at 2 K.

Entropy and magnetocaloric effect in ferrimagnets RCo2

The equations of state for the magnetic and elastic subsystems of a ferrimagnet are obtained in terms of the exchange–striction model. In the formulas derived for magnetic entropy, it is represented as the sum of the contributions of two magnetic sublattices of the ferrimagnet. One of the main characteristics of the magnetocaloric effect, viz., isothermal variation ΔS iso of the entropy in a magnetic field, is calculated for compounds RCo2 (R = Er, Ho, Dy) that experience a first-order magnetic phase transition and TbCo2 that experiences a second-order magnetic phase transition. It is shown that the calculated values of ΔS iso for these compounds are in satisfactory quantitative agreement with experimental results. The change in the entropy of a ferrimagnet in a strong magnetic field upon a transition from the ferrimagnetic to ferromagnetic ordering is calculated. The peculiarities in the magnetic field dependences of the magnetic entropy of a two-sublattice ferrimagnet are analyzed.

Electric field tuning of magnetocaloric effect in FeRh0.96Pd0.04/PMN-PT composite near room temperature

The first-order magnetic phase transition alloy, FeRh, exhibits a large magnetocaloric effect well above room temperature and works in a limited refrigeration temperature region, which hinders its application to some extent. In the present work, we report a remarkable electric-control magnetocaloric effect in the FeRh0.96Pd0.04/PMN-PT composite near room temperature through strain-mediated magnetoelectric coupling. By applying an electric field of 8 kV/cm, the metamagnetic phase transition temperature of the FeRh0.96Pd0.04 film shifts from 300 to 325 K. As a result, the refrigeration temperature region is broadened from 35 to 47 K. These results indicate that applying multiple driving fields is an effective method for tuning the magnetocaloric effect.

Femtosecond single-shot imaging and control of a laser-induced first-order phase transition in HoFeO3

Excitation of antiferromagnetic HoFeO3 with a single 80 fs laser pulse triggers a first-order spin-reorientation phase transition. In the ultrafast kinetics of the transition one can distinguish the processes of impulsive excitation of spin precession, nucleation of the new domain and growth of the nuclei. The orientation of the spins in the nuclei is defined by the phase of the laser-induced coherent spin precession. The growth of the nuclei is further promoted by heating induced by the laser excitation. Hereby we demonstrate that in HoFeO3 coherent control of the spin precession allows an effective control of the route of the heat-induced first-order magnetic phase transition. The theoretical description of the excitation of the spin precession by linearly-polarized ultrashort laser pulses is developed with the sigma model. The analysis showed high sensitivity of the excited dynamics to the initial spin orientations with respect to the crystallographic axes of the material.

Investigation of the magnetocaloric effect in correlated metallic systems with Van Hove singularities in the electron spectrum

In this work, the magnetic contribution to the isothermal entropy change ΔS upon switching on a magnetic field has been investigated in correlated metallic ferromagnets within the Hubbard nondegenerate model. The analytical expression ΔS for obtained in the mean-field approximation depends substantially on the electronic structure (density of electron states), which presents new ways to increase the absolute value of ΔS relative to the known result obtained within the Heisenberg model. The temperature dependence of ΔS has been calculated at different values of the Coulomb interaction U and the number of electrons n for the Bethe infinite-dimensional lattice and square lattice with allowance for transfer integrals in the first (t) and the second (t') coordination shells. It has been found that the presence of Van Hove singularities in the electronic spectrum near the Fermi level makes it possible to considerably increase |ΔS| at a fixed magnetic field. The possibility of first-order magnetic phase transitions depending on the model parameters has been analyzed.

Магнітні фазові переходи першого роду в нанокластерних системах в рамках наближення Ландау

Магнітні фазові переходи першого роду в нанокластерних системах в рамках наближення Ландау

Microstructure, magnetic and magnetocaloric properties of Fe2–x Mn x P0.4Si0.6 alloys

The present work is devoted to investigating the microstructure, magnetism and magnetocaloric effects of Si- and Mn-rich FeMn(P,Si) alloys. The Mn-substituted alloys with Fe2– x Mn x P0.4Si0.6 ( x = 1.25, 1.30, 1.35, 1.40, 1.45 and 1.50) were prepared by high-energy ball milling and solid-state reaction. Experimental results show that the alloys crystallized into a majority Fe2P-type hexagonal structure, coexisting with minor amounts of (Mn,Fe)3Si and (Mn,Fe)5Si3 phases. The Curie temperature decreased linearly from 321 to 266 K with increasing Mn content from 1.25 to 1.50 in Fe2– x Mn x P0.4Si0.6 alloys. The first-order magnetic phase transition became weakened and the second-order magnetic phase transition became dominated with increasing Mn content. Fe0.75Mn1.25P0.4Si0.6 alloy presents a maximum isothermal magnetic-entropy changes of 7.2 J (kg K)–1 in a magnetic field change of 0–1.5 T. The direct measurement shows that Fe0.7Mn1.3P0.4Si0.6 and Fe0.65Mn1.35P0.4Si0.6 alloys exhibit a maximum adiabatic temperature change of 1.8 K in a magnetic field change of 0–1.48 T. The thermal hysteresis for all alloys is less than 4 K. These experimental results reveal that Fe2– x Mn x P0.4Si0.6 alloys could be a candidate material for magnetic refrigeration.

Low-temperature anomalous magnetic behavior of Co2TiO4 and Co2SnO4

We report the low-temperature anomalous magnetic behavior of ferrimagnetic spinels cobalt orthotitanate (Co2TiO4), which exhibits magnetic compensation behavior across 31.74 K, and cobalt orthostannate (Co2SnO4) exhibiting two sequential magnetic transitions, namely (i) ferrimagnetic to paramagnetic transition with Néel temperature TN ∼ 41 K and reentrant spin-glass behavior with glass transition temperature TSG ∼ 39 K. The Arrott plot (H/M versus M2) criterion has been used to extricate the order of sequential magnetic transitions occurring below TN. Negative slopes of the Arrott plots below 32 K, metamagnetic-like character of the M-H isotherms, anomalies in the specific-heat (CP T−1 versus T) below 15 K, and a zero-crossover of isothermal magnetic-entropy-change (ΔS) signify the presence of pseudo first-order discontinuous magnetic phase transition in the low-temperature regime 5 K ≤ T ≤ 32 K. The dc- and ac-susceptibilities of both Co2TiO4 and Co2SnO4 are interpreted in terms of frozen-spin-clusters, which are responsible for very large magnitudes of the coercivity HC ∼ 20 kOe and bipolar-exchange bias HEB ∼ −20 kOe observed below 10 K.

Electric control of magnetism and magnetocaloric effects in LaFe11.4Si1.6H1.5 using ferroelectric PMN–PT

The alloy with first-order magnetic phase transition has an advantage to exhibit large magnetoelectric effect in strain-mediated multiferroic composites, since the strain can drive its phase transition and consequently lead to a large magnetic change. In the present paper, we investigate the electric field manipulation of magnetic and magnetocaloric properties in LaFe11.4Si1.6H1.5/Pb(Mg1/3Nb2/3)O3–PbTiO3 laminate. By applying an electric field on the ferroelectric substrate, the relative change of magnetization has a peak value of −8% around the Curie temperature, showing a large converse magnetoelectric effect. As for the magnetocaloric performance, the peak temperature of magnetic entropy change (ΔSM) has a shift of 3 K to low temperature and the maximal value of ΔSM keeps almost unchanged under an electric field of 8 kV cm−1. Moreover, the thermal and magnetic hysteresis can be reduced as well with the application of the electric field.

Universal curves in assessing the order of magnetic transition of La0.7−xPrxCa0.3MnO3 compounds exhibiting giant magnetocaloric effect

The magnetic properties of La0.7-xPrxCa0.3MnO3 (x = 0.0, 0.2, 0.3, 0.4, and 0.5) compounds fabricated by a solid-state reaction are studied by using Arrott plots and universal curves. The Arrott plots near the Curie temperature show negative slopes over the entire magnetic field range up to 50 kOe, indicating a first-order magnetic phase transition (according to Banerjee's criterion) for the x = 0.0, 0.2, 0.3, and 0.4 samples. For the x = 0.5 sample, however, the plots show positive slopes at low magnetic fields below 10 kOe, indicating a second-order transition. These results are further checked by universal curves of the normalized entropy change versus reduced temperature. The universal curves show a divergence among the curves with different magnetic fields for a first-order magnetic transition, but for a second-order transition, they collapse onto the same curve. The Curie temperature, around which the maximum magnetic entropy change occurs, decreases continuously from 260 to 110 K as x increases from 0.0 to 0.5. In the same x range, the maximum entropy change measured at a magnetic field span of 50 kOe decreases from 10.70 to 7.14 J/kg K, but the relative cooling power increases from 278 to 380 J/kg under the same magnetic field span.

Влияние объёмной магнитострикции на мартенситное превращение в сплавах железа. Магнитный фазовый переход первого рода

Влияние объёмной магнитострикции на мартенситное превращение в сплавах железа. Магнитный фазовый переход первого рода

Prediction of magnetocaloric effect in La0.8SrxCa0.2−xMnO3 compounds (x = 0.05, 0.1 and 0.15) with a first-order magnetic phase transition

In this paper, we have studied structural and magnetocaloric properties of La0.8SrxCa0.2−xMnO3 system with x = 0.05, 0.1 and 0.15. X-ray diffraction (XRD) indicates that samples with x = 0.05 and x = 0.1 crystallize in an orthorhombic structure in Pnma space group, whereas the sample with x = 0.15 crystallize in the rhombohedral structure with R3¯c space group. The field dependence of magnetocaloric properties of manganite La0.8SrxCa0.2−xMnO3 undergoing first order phase transition is investigated using a phenomenological model. The magnetic entropy change of the samples varies from 1.01 J/kg K for x = 0–1.57 J/kg K for x = 0.15 under the applied magnetic field of 12 kOe. These results indicate that the present compounds are one of candidate materials for magnetic refrigerators near room temperature.

Structure, magnetic and magnetothermal properties of the non-stoichiometric ErCo2Mnx alloys

The structure, magnetic and magnetothermal properties and heat capacity of the ErCo2Mnx (0 ≤ x ≤ 1.4) non-stoichiometric alloys have been studied. It is shown that the alloys with x ≤ 0.8 are almost single-phase with the MgCu2-type Laves-phase structure, while the alloys for x ≥ 1.0 contain considerable amount of the cubic Th6Mn23-type phase. Alloying with manganese leads to a substantial increase in the exchange interactions. For the binary ErCo2 compound, the magnetization shows a first-order magnetic phase transition with the Curie temperature TC = 35 K. For all the Mn-containing alloys studied, the transition is found to be the second-order type; the Curie temperature in ErCo2Mnx sharply growths with increasing x and reaches its maximum value 212 K for the ErCo2Mn0.6 alloy. Using the magnetization data and the results of the heat capacity measurements, we estimated the magnetocaloric effect for these compounds. The obtained results are discussed on the assumption of a strong variation of the 3d-metal magnetic moments upon alloying with Mn.

Study of magnetic transition and magnetic entropy changes of Pr0.6Sr0.4MnO3 and Pr0.6Sr0.4Mn0.9Fe0.1O3 compounds

In the present work, we analyze the magnetic transition and magnetic entropy change $ \vert\Delta S_{M}\vert$ of Pr0.6Sr0.4Mn1-x Fe x O3 samples. Using Arrott plots, we report that the phase transition for Pr0.6Sr0.4MnO3 sample is of second order, while the Pr0.6Sr0.4Mn0.9Fe0.1O3 sample exhibits a first-order magnetic phase transition. From the magnetization measurements at temperature close to the Curie temperature, the magnetic entropy change, $ \vert\Delta S_{M}\vert$ and the Relative Cooling Power (RCP) have been estimated. The maximum of magnetic entropy change $ \vert\Delta S_M^{\max}\vert$ reaches, under an applied magnetic field of 5T, 3.58 and 3.66J/kg K for Pr0.6Sr0.4MnO3 and Pr0.6Sr0.4Mn0.9Fe0.1O3, respectively. The RCP values have been estimated to 159.37 and 223.52J/kg. For both samples, the $ \vert\Delta S_{M}\vert$ values evaluated using the Maxwell theory were found in accordance with those calculated by the Landau theory.

Magnetic and magnetocaloric properties in La0.7Ca0.3−xNaxMnO3 exhibiting first-order and second-order magnetic phase transitions

Polycrystalline orthorhombic samples La0.7Ca0.3−xNaxMnO3 (x = 0–0.09) were prepared by solid-state reaction. The study of magnetic properties revealed that the ferromagnetic-paramagnetic (FM-PM) transition temperature (TC) increases from 255 to about 271 K with increasing Na-doping content (x) from 0 to 0.09, respectively. Around the TC, we have found the samples showing a large magnetocaloric (MC) effect with maximum values of magnetic entropy change (|ΔSmax|) of 7–8 J kg−1 K−1 and relative cooling power RCP = 232–236 J/kg for the samples x = 0.03–0.09 in a magnetic-field interval ΔH = 40 kOe. Detailed analyses of isothermal magnetization data M(T, H) based on Banerjee's criteria indicated a first-to-second-order magnetic-phase transformation taking place at a threshold Na-doping concentration xc ≈ 0.06. This could also be observed clearly from the feature of entropy universal curves. An assessment of the magnetic-ordering exponent N = dLn|ΔSm|/dLnH demonstrates an existence of short-range magnetic order in the samples. We believe that the changes of the magnetic properties and MC effect in La0.7Ca0.3−xNaxMnO3 caused by Na doping are related to the changes in the structural parameters and Mn4+/Mn3+ ratio, which are confirmed by the geometrical and electronic analyses based on X-ray diffraction and X-ray absorption fine structure.