Specific heat and entropy change at the first order phase transition of La(Fe-Mn-Si)13-H compounds

Basso, Vittorio; Küpferling, Michaela; Bennati, Cecilia; Barzca, Alexander; Katter, M.; Bratko, Milan; Lovell, Edmund; Turcaud, J.A.; Cohen, L. F.

doi:10.1063/1.4928086

Cited by 68 publications

(61 citation statements)

References 20 publications

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“…As reported elsewhere [7], the addition of hydrogen raises the magnetic transition temperature; here by 154K, 156K and 157K in samples M, N and O respectively. The magnetic transition is sharpest (most first-order) and has largest hysteresis for the lowest Mn content samples as reported by Basso et al [18], and this is true for both the hydrogenated and dehydrogenated series [19]. The saturation magnetisation in a 1T field decreases with Mn addition and it was originally suggested that Mn adds antiferromagnetically into the lattice, as simple dilution (substitution of Mn for Fe) is unable to account for the magnitude of the decrease [8].…”

Section: Experimental Methodssupporting

confidence: 49%

Low-temperature specific heat in hydrogenated and Mn-dopedLa(Fe,Si)13

et al. 2016

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It is now well established that the paramagnetic to ferromagnetic transition in the magnetocaloric La(FeSi)13 is a cooperative effect involving spin, charge and lattice degrees of freedom. However, the influence of this correlated behaviour on the ferromagnetic state is as yet little studied. Here we measure the specific heat at low temperatures in a systematic set of LaFexMnySiz samples with and without hydrogen, to extract the Sommerfeld coefficient, the Debye temperature and the spin wave stiffness. Substantial and systematic changes in magnitude of the Sommerfeld coefficient are observed with Mn substitution and introduction of hydrogen, showing that over and above the changes to the density of states at the Fermi energy there are significant enhanced d band electronic interactions, at play. The Sommerfeld coefficient is found to be 90-210 mJmol -1 K -2 unusually high compared to that expected from band structure calculations. The Debye temperature determined from the specific heat measurement is insensitive to Mn and Si doping, but increases when hydrogen is introduced into the system. The Sommerfeld coefficient is reduced in magnetic field for all compositions that have a measurable spin wave contribution. These results move our understanding of the cooperative effects forward in this important and interesting class of materials significantly, and provides a basis for future theoretical development.

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Section: Experimental Methodssupporting

confidence: 49%

Low-temperature specific heat in hydrogenated and Mn-dopedLa(Fe,Si)13

et al. 2016

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“…23 Figure 3 shows the TC and the Tcrit across the series using this method. The Tcrit has been identified as the point of vanishing hysteresis in the specific heat measurement for the hydrogenated samples (as reported in Basso et al 23 ) and in the magnetization measurements for the samples without hydrogen. It can be observed in figure 3(a) that TC changes systematically with introduction of Mn and that the same is true of the hydrogenated samples with their much higher TC.…”

Section: Fig 2 Ac Heat Capacity (A) Increases With Field/temperaturmentioning

confidence: 99%

“…23 In this paper we consider the matching family of La(Fe, Mn, Si)13 materials (that is without the hydrogenation). We consider the order of the transition by extracting the latent heat explicitly and show how it is suppressed in applied magnetic field as the critical point is approached.…”

Section: Introductionmentioning

confidence: 99%

Determining the first-order character ofLa(Fe,Mn,Si)13

et al. 2017

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Definitive determination of first order character of the magnetocaloric magnetic transition remains elusive. Here we use a microcalorimetry technique in two modes of operation to determine the contributions to entropy change from latent heat and heat capacity separately in an engineered set of La(Fe, Mn, Si)13 samples. We compare the properties extracted by this method with those determined using magnetometry and propose a model independent parameter that would allow the degree of first order character to be defined across different families of materials. The microcalorimetry method is sufficiently sensitive to allow observation of an additional peak feature in the low field heat capacity associated with the presence of Mn in these samples. The feature is of magnetic origin but is insensitive to magnetic field, explicable in terms of inhomogeneous occupancy of Mn within the lattice resulting in antiferromagnetic ordered Mn clusters.

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“…Figure 2 shows the heat flux q s measured by Peltier calorimetry on a LaFe 11.60 Mn 0.18 Si 1.22 -H 1.65 fragment of mass m = 4.79 mg, close to the transition, as a function of time t. The experimental data refer to heating scans performed at 1 mK/s rate at increasing applied magnetic field H. It is clear the presence of subsequent heat flux avalanches increasing in number by increasing H. Each avalanche is characterized by an initial linear growth and an exponential decay whose slope and time constant change with the field. In particular, as soon as H is getting closer to the critical field µ 0 H c ∼ 2.2 T (µ 0 being the vacuum permeability) the transition becomes more and more of second order type [8] and the avalanches start to be less clearly distinguishable from the background signal. The avalanches are related to the presence of latent heat, while the background is due to the reversible part of the specific heat of the system.…”

Section: Thermodynamic Theory Of Heat Flux Avalanchesmentioning

confidence: 99%

“…2). We use experimental data provided by Peltier calorimetry under magnetic field performed at 1 mK/s rate on LaFe 11.60 Mn 0.18 Si 1.22 -H 1.65 compounds [8]. In Sec.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of heat flux avalanches at the first order transition in La(Fe-Mn-Si)₁₃-H_1.65 compounds

Piazzi

Bennati

Basso

2017

J. Phys.: Conf. Ser.

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Abstract. We study heat flux avalanches occurring at the first order transition in La(Fe-MnSi)13-H1.65 magnetocaloric material. As the transition is associated to the phase boundaries motion that gives rise to the latent heat, we develop a non equilibrium thermodynamic model. By comparing the model with experimental calorimetry data available for Mn=0.18, we find the values of the intrinsic kinetic parameter RL, expressing the damping for the moving boundary interface, at different magnetic fields. We conclude that by increasing field, thus approaching the critical point, the avalanches increase in number and their kinetics is slowed down. IntroductionThe kinetics underlying the first order ferromagnetic (FM) to paramagnetic (PM) transitions of La(Fe-Si) 13 and related magnetocaloric materials is still an open issue [1][2][3][4]. Novel aspects about this feature can be learnt by analyzing heat flux signals obtained through temperature scans at very low rates [5,6]. Indeed, the low scan rate allows to distinguish single heat flux avalanches associated to the microscopic individual processes occurring during the phase transition. Then, the characteristic times governing the behaviour of the avalanches are also those determining the kinetics of the transition. In particular, these indications may help to further improve the working frequency of magnetic refrigerators [1].We develop a model, based on the non equilibrium thermodynamic theory of linear systems [7], in which the kinetics of first order transitions is related to the FM-PM phase boundaries motion. The model allows to describe single heat flux avalanches through an intrinsic kinetic parameter R L relating the change in latent heat to the difference between the transition temperature T t and the sample temperature T s (Sec. 2). We use experimental data provided by Peltier calorimetry under magnetic field performed at 1 mK/s rate on LaFe 11.60 Mn 0.18 Si 1.22 -H 1.65 compounds [8]. In Sec. 3 we present the results of the comparison between the model and the experimental data, while in Sec. 4 we discuss them.

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Specific heat and entropy change at the first order phase transition of La(Fe-Mn-Si)13-H compounds

Cited by 68 publications

References 20 publications

Low-temperature specific heat in hydrogenated and Mn-dopedLa(Fe,Si)13

Low-temperature specific heat in hydrogenated and Mn-dopedLa(Fe,Si)13

Determining the first-order character ofLa(Fe,Mn,Si)13

Kinetics of heat flux avalanches at the first order transition in La(Fe-Mn-Si)₁₃-H_1.65 compounds

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Specific heat and entropy change at the first order phase transition of La(Fe-Mn-Si)13-H compounds

Cited by 68 publications

References 20 publications

Low-temperature specific heat in hydrogenated and Mn-dopedLa(Fe,Si)13

Low-temperature specific heat in hydrogenated and Mn-dopedLa(Fe,Si)13

Determining the first-order character ofLa(Fe,Mn,Si)13

Kinetics of heat flux avalanches at the first order transition in La(Fe-Mn-Si)13-H1.65 compounds

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Kinetics of heat flux avalanches at the first order transition in La(Fe-Mn-Si)₁₃-H_1.65 compounds