Conventional Magnetocaloric Effect Research Articles

Conventional and inverse magnetocaloric effects in La0.45Sr0.55MnO3 nanoparticles

The magnetocaloric effect of La0.45Sr0.55MnO3 nanoparticles was studied by dc magnetization measurements. A sample with mean particle size of about 140 nm exhibits both a conventional magnetocaloric effect around the Curie temperature (≈ 295 K) and a large inverse magnetocaloric effect around the antiferromagnetic-ferromagnetic transition temperature (≈ 200 K). The change of magnetic entropy increases monotonically with applied magnetic field and reaches the values of 5.51 J/kg K and − 2.35 J/kg K at 200 K and 295 K, respectively, in an applied field of 5 T. The antiferromagnetic-ferromagnetic transition is absent in a 36 nm size sample, which shows only a broad ferromagnetic transition around 340 K and a small change in magnetic entropy near room temperature. The results are discussed in terms of the entropy difference between the A-type antiferromagnetic ground state of La0.45Sr0.55MnO3 and the low moment ferromagnetic state. By comparing the results obtained on nanoparticles and bulk La0.45Sr0.55MnO3, one can conclude that the inverse magnetocaloric effect in a material showing the antiferromagnetic-ferromagnetic transition could be improved over a wide range of temperature by tuning the spin disorder in the antiferromagnetic state.

Reversibility and irreversibility of magnetocaloric effect in a metamagnetic shape memory alloy under cyclic action of a magnetic field

We have studied adiabatic temperature change ΔTad in a Ni50Mn36Co1Sn13 metamagnetic shape memory alloy. An irreversible character of ΔTad has been observed in the vicinity of the reverse martensitic transformation. In this region, cyclic application of the magnetic field converts comparatively large inverse magnetocaloric effect (MCE) with ΔTadmax=−0.8 K to a weaker conventional MCE (ΔTadmax=0.3 K). The crossover of ΔTad has been attributed to the irreversible character of the magnetic field-induced transformation and the closeness of the martensitic transformation and Curie temperature of the austenitic phase TCA.

A comparative study of the magnetocaloric effect in RNi 2 (R = Dy, Ho, Er) intermetallic compounds

In this work we study the conventional and anisotropic magnetocaloric effects in the cubic rare-earth RNi 2 (R = Dy, Ho, Er) ferromagnetic intermetallic compounds. For each of these compounds we have explored the crystalline electrical-field anisotropy to predict the anisotropic magnetocaloric quantities under rotations of an applied magnetic field of constant intensity. The calculations were performed using proper parameters reported in the literature. Our results for the anisotropic magnetocaloric effect reveal some peculiarities of the spin reorientation which can be considered in designing new magnetocaloric materials for magnetic refrigerators.

Inverse and conventional magnetic entropy change in La0.8Sm0.2Mn2Si2 and La0.775Gd0.225Mn2Si2 compounds

The magnetic and magnetocaloric properties of La0.8Sm0.2Mn2Si2 and La0.775Gd0.225Mn2Si2 compounds have been studied by temperature- and magnetic field-dependent magnetic measurements. Both compounds crystallize in the ThCr2Si2-type structure with the space group I4/mmm. Both compounds exhibit reentrant magnetic phase transitions and field-induced transitions from antiferromagnetic to ferromagnetic or ferrimagnetic state. The isothermal magnetic entropy change is estimated by using the Maxwell relation and Landau theory. Both compounds show inverse and conventional magnetocaloric effects around transition temperatures. Application of Landau theory on magnetic transitions shows good agreement with the result obtained by Maxwell theory.

ChemInform Abstract: Ni‐Mn‐based Magnetic Shape Memory Alloys: Magnetic Properties and Martensitic Transition

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Magnetic transitions in the Gd 5Si 4− xP x ( x = 0.5, 0.75, 1.25) phases. Magnetocaloric effect of the Gd 5Si 2.75P 1.25 phase

The Gd 5Si 2.75P 1.25 phase with all interslab Si/P–Si/P dimers broken (Sm 5Ge 4-type structure) undergoes a ferromagnetic transition at 184 K. For this phase, the magnetocaloric effect in terms of the magnetic entropy change, Δ S, reaches the maximum value of −7.8 J/kg K at 177 K. Absence of a temperature-dependant structural transition, as confirmed by the low-temperature single crystal diffraction studies, together with the moderate value of Δ S points to the presence of a conventional magnetocaloric effect. Gd 5Si 3.5P 0.5 and Gd 5Si 3.25P 0.75, which are composites of the Gd 5Si 4- (all Si/P–Si/P dimers intact) and Sm 5Ge 4-type phases, possess two magnetic transitions associated with the two-phases. Introduction of P into Gd 5Si 4 lowers the Curie temperature from 336 K to 332 K in Gd 5Si 3.25P 0.75.

A comparative study of the magnetocaloric effect in RNi2 (R=Nd,Gd,Tb) intermetallic compounds

Conventional and anisotropic magnetocaloric effects were studied in cubic rare earth RNi2 (R=Nd,Gd,Tb) ferromagnetic intermetallic compounds. These three compounds are representative of small, null, and large magnetocrystalline anisotropy in the series, respectively. Magnetic measurements were performed in polycrystalline samples in order to obtain the isothermal magnetocaloric data, which were confronted with theoretical results based on mean field calculations. For the R=Tb case, we explore the crystalline electrical-field anisotropy to predict the anisotropic magnetocaloric behavior due to the rotation of an applied magnetic field of constant intensity. Our results suggest the possibility of using both conventional and anisotropic magnetic entropy changes to extend the range of temperatures for use in the magnetocaloric effect.

Magnetocaloric effect in Heusler alloysNi50Mn34In16 and Ni50Mn34Sn16

We present results of detailed ac susceptibility, magnetization and specific heat measurements in Heusleralloys Ni50Mn34In16 and Ni50Mn34Sn16. These alloys undergo a paramagnetic to ferromagnetic transition around305 K, which is followed by a martensitic transition in the temperature regimearound 220 K. Inside the martensite phase both the alloys show signatures offield-induced transition from martensite to austenite phase. Both field- andtemperature-induced martensite–austenite transitions are relatively sharp inNi50Mn34In16. We estimate the isothermal magnetic entropy change and adiabatic temperature changeacross the various phase transitions in these alloys and investigate the possible influence ofthese transitions on the estimated magnetocaloric effect. The sharp martensitic transition inNi50Mn34In16 gives rise to a comparatively large inverse magnetocaloric effect across this transition. Onthe other hand the magnitudes of the conventional magnetocaloric effect associatedwith the paramagnetic to ferromagnetic transition are quite comparable in thesealloys.

Ni–Mn-based magnetic shape memory alloys: Magnetic properties and martensitic transition

We report a compilation of the structural and magnetic properties of Ni–Mn-based magnetic alloys with special attention to those which undergo martensitic transformations. We discuss the effect of the coupling between structure and magnetism on the properties of these alloys and how this coupling affects their martensitic transition. We show that as a consequence of such a coupling, these alloys exhibit an unusual magneto-mechanical and magneto-thermal behaviour which gives rise to singular functional properties such as magnetic shape memory and magnetic superelasticity, as well as conventional and inverse giant magnetocaloric effects.

Cooling and heating by adiabatic magnetization in theNi50Mn34In16magnetic shape-memory alloy

We report on measurements of the adiabatic temperature change in the inverse magnetocaloric ${\mathrm{Ni}}_{50}{\mathrm{Mn}}_{34}{\mathrm{In}}_{16}$ alloy. It is shown that this alloy heats up with the application of a magnetic field around the Curie point due to the conventional magnetocaloric effect. In contrast, the inverse magnetocaloric effect associated with the martensitic transition results in the unusual decrease of temperature by adiabatic magnetization. We also provide magnetization and specific heat data which enable to compare the measured temperature changes to the values indirectly computed from thermodynamic relationships. Good agreement is obtained for the conventional effect at the second-order paramagnetic-ferromagnetic phase transition. However, at the first-order structural transition the measured values at high fields are lower than the computed ones. Irreversible thermodynamics arguments are given to show that such a discrepancy is due to the irreversibility of the first-order martensitic transition.