Workshop on i-Caloric Effects 2023

From 26th to 27th April Every day from 09h00 to 18h00

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About the Event

The Workshop on i-caloric effects (WiCE) is a scientific event that brings together researchers from different fields to discuss the latest advancements in the field of i-caloric materials and their potential applications. i-Caloric materials are those that exhibit a reversible temperature change under the application or removal an external stimuli. This unique property makes them promising candidates for use in energy-efficient refrigeration and heat pump systems.

2023 is the second edition and, during the two workshop days, experts will share their research findings, discuss the challenges in developing i-caloric materials, and explore potential applications of these materials in various fields. The workshop provides a platform for researchers to collaborate and exchange ideas, which helps to accelerate progress in this exciting and rapidly growing field. By fostering collaboration and innovation, the Workshop on i-Caloric Effects is playing a crucial role in advancing the development of i-caloric materials and their potential applications, which have the potential to revolutionize the energy industry.

Also, for this year we make our tribute to a friend and mentor Professor Vitalij Pecharsky, a brilliant researcher and a pioneer in the field of i-caloric effect, who left us very early. The legacy of Professor Pecharsky will live on through the countless lives he touched and the countless minds he inspired. We will forever be grateful for his contributions to science and his unwavering commitment to advancing knowledge for the betterment of humanity.
The organizer wishes all participants a pleasurable workshop!

Paula Alho, on behalf of the organizing committee

WiCE 2023 Organizing Committee
Alexandre M. G. Carvalho
Bruno de Pinho Alho
Paula O. Ribeiro Alho
Paulo Vinícius Trevizoli
Vivian M. Andrade

The WiCE 2023 booklet can be accessed here

Speakers

Catalina Salazar Mejia
Bikram Bhatia
João Amaral
Yuriy Koshkid'ko
Nilson A. de Oliveira
Paulo de Faria
Pedro von Ranke
Pol Lloveras
Urban Tomc
Yaroslav Mudryk
Bruno Alho
João Horta Belo
Victorino Franco
Alan T. D. Nakashima
Jaka Tušek
Jierong Liang
Luana Caron
Mario Reis
Vladimir I. Zverev
Jia Yan Law

09h10 Opening Session Opening +

Place: Sala 1

WiCE 2023 Opening Session by Paula Alho

09h30 - Catalina Salazar Mejia Materials with first-order transition and inverse magnetocaloric effect and their peculiarities Presentation +

Place: Sala 1

NiMn-based Heusler alloys and Fe-Rh compounds have been widely studied due to their large inverse magnetocaloric effect (MCE) [1,2,3] and other interesting properties [4,5] originating from the first-order magnetostructural transition their are exhibiting. In general, the low-temperature phase has a lower magnetic moment and lower volume than the high-temperature one. Therefore, not only the magnetization changes during this transformation, but also the volume of the crystal lattice. Consequently, a magnetic field shifts the transition towards lower temperatures, while applying hydrostatic or uniaxial pressure shifts it toward higher temperatures. The transition can be induced by magnetic-field application resulting in an inverse MCE - the cooling of the material [6]. We have widely studied these alloys in pulsed magnetic fields, specifically, measuring the adiabatic temperature change, DeltaTad. In this work, we present an overview of the DeltaTad characterization in magnetic fields up to 50 T through different examples of NiMn-based Heusler alloys and Fe-Rh compounds. We show the general characteristics of the MCE of this class of materials and discuss their peculiarities.

References:

[1] A. M. Chirkova et al., Phys. Rev. Mater., 5, 064412 (2021)

[2] M. Ghorbani Zavareh et al., Appl. Phys. Lett. 106, 071904 (2015)

[3] T. Gottschall et al., Phys. Rev. Appl. 5, 024013 (2016)

[4] C. Salazar Mejía et al., Appl. Phys. Lett. 110, 071901 (2017)

[5] B. Beckmann et al., Acta Mater., 246, 118695 (2023)

[6] O. Gutfleisch et al., Phil. Trans. R. Soc. A, 374, 20150308 (2016)

10h00 - Jierong Liang Design perspectives of magnetocaloric devices Presentation +

Place: Sala 1

In the pursuit of commercializing magnetic refrigeration, MAGNOTHERM Solutions GmbH has been advancing practical applications that connect various technologies related to magnetocaloric devices with active magnetic regenerators (AMRs). This presentation provides an overview of design concepts, including AMR performance metrics, architectures, and topologies. Two prototypes are analyzed: the magnetocaloric heat pump at DTU (MagQueen) and the magnetocaloric beverage cooler at MAGNOTHERM (Polaris). For the MagQueen with a parallel AMR design, the heating capacity and COP are compared using 10-layer La(Fe,Mn,Si)13Hy and single-layer Gd fillings. For the Polaris with a series AMR design, the temperature span of seven AMRs with different shapes is analyzed. Additionally, the study identifies the fluid pump as the most inefficient component in Polaris. The challenges of using layered La(Fe,Mn,Si)13Hy AMRs in the prototype are highlighted, emphasizing the need for accurate control of temperature profiles along each AMR. The efficiencies of external components for the magnetocaloric devices are also critical to promote the competitiveness of magnetic refrigeration products.

10h30 Break Coffee break +

Place: Sala 1

break

10h50 - João Horta Belo LaFe11.6Si1.4 magnetic field-induced (iso)structural transition kinetics probed with time-dependent X-ray Diffraction Presentation +

$LaFe11.6Si1.4 magnetic field-induced (iso)structural transition kinetics probed with time-dependent X-ray Diffraction$

Place: Sala 1

Magnetic refrigeration, one of the most promising alternatives to conventional cooling/heating technology, makes use of magnetocaloric effect (MCE) which is maximized in materials that exhibit a strong magnetovolume coupling associated with first-order phase transitions (FOPTs), such as Gd5(Si,Ge)4 and La(Fe,Si)13 [1]. In order to optimize a magnetic heat pump efficiency, one approach is to enhance its frequency – and for that the fundamental knowledge about the time required for the materials to undergo these FOPTs is crucial. From recent literature, it has been demonstrated that magnetic transitions can range up to 100s and strongly depends on the sample shape, temperature and magnetic field [2]. Since FOPT transitions occur in strong spin-lattice coupled materials, it is expected that, in parallel with the magnetization time-dependent evolution, there must be a crystal structure time-dependent evolution.

In this work, we present for the first time (to the best of our knowledge) time-dependent evolution of the cubic structure of a LaFe11.6Si1.4 sample across its magnetovolume transition probed by Synchrotron XRD as a function of temperature, magnetic field, time, and direction of the transition. The time-scales and the evolution profiles of the lattice parameter as a function of time (Figure 1 b)) are shown to strongly depend on the field and temperature. Remarkably a strong asymmetry was also observed between the timescales of the transition triggered by increasing field (typically few hundreds of seconds) versus decreasing field (below 1 second). Through free energy estimates of a compressible Ising model system [3], it is shown that this assymetry correlates with the free energy barrier between stable and metastable states. In the field decreasing process, this barrier is small, or even non-existent, in contrast to the field increasing process.

Acknowledgments: We would like to acknowledge FCT, for the funded projects PTDC/EME-TED/3099/2020 (IFIMUP), project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020 and the the Deutsche Forschungsgemeinschaft (DFG) within the CRC/TRR 270 (Project-ID 405553726). A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory.

References:

[1] T. Gottschall, K. Skokov, et al. Adv. Ener. Mater., 9, 1901322 (2019)

[2] E. Lovell, A. M. Pereira, D. Caplin, J. Lyubina, L.F. Cohen, Adv. Ener. Mater. 14016394 (2014)

[3] J. S. Amaral and V. S. Amaral, Front. Mater 10 1037396 (2023).

11h10 - Luana Caron Fe2P-based materials for magnetocaloric applications Presentation +

Place: Sala 1

This year it makes 21 years since the ground breaking paper of Tegus in Nature has been published, kick-starting the research of Fe2P-based materials for magnetocaloric applications. In parallel with systematic compositional tuning experiments aimed at creating phase diagrams relevant for applications, intense research was done on the physics of the phase transition itself. These materials are hexagonal ferromagnets which undergo an order-disorder phase transition which is first order in nature due to the strong coupling to the lattice but with low to no volume change. This makes these materials extremely interesting for applications due to the low hysteresis lossess upon cycling. In this presentation I will attempt to give an overview of what we have learned about this class of materials and give you arguments of why their properties make them the most promising materials for applications.

11h40 Break Coffee break +

Place: Sala 1

break

13h00 - Pol Lloveras Strongly disordered materials for colossal barocaloric effects Presentation +

Place: Sala 1

Order-disorder first-order phase transitions are attracting interest for thermal management because they may lead to large heat exchange to the energy stored in the disordered phases. Moreover, concomitant volume changes in these transitions may allow an active control of the heat exchange by means of application of pressure, which leads to conceive barocaloric methods for solid-state cooling and heat pumping [1]. Interestingly, these mehods could offer a more environmentally friendly and efficient alternative to harmful vapor compression. In the last years, progress on materials research has allowed the identification of outstanding barocaloric agents such as some organic plastic crystals with colossal barocaloric effects much above 100 J K-1 kg-1. Unfortunately, typically moderate or large hysteresis and a moderate sensitivity of the transition to pressure make these colossal barocaloric effects often require pressure changes well above 100 MPa to obtain reversible effects, which limits their potential applicability. Here we present two recently investigated materials with relatively little-hysteretic yet highly non-isochoric phase transitions that originate strong disorder in the high temperature phase. These features allow to obtain reversible colossal barocaloric effects below 100 MPa in both compounds, with simultaneously large values for isothermal entropy changes DeltaS and adiabatic temperature changes DeltaT . One material is a layered organic-inorganic pseudoperovskite [2] whose disorder is associated with the melting-like process and rotation of the organic chain linked to the inoganic octahedra. It displays reversible DeltaS~230 J K−1 kg−1 under low pressure changes of 50 MPa, and reversible DeltaT~10 K under pressure changes of 80 MPa. The other material is a fast-ion conductor [3] displaying strong molecular orientational and vibrational disorder of anions coupled to diffusion of cations. In that case, the material undergoes reversible DeltaS~200 J K−1 kg−1 and DeltaT~10 K under pressure changes of 100 MPa. Here, the high transition temperature suggests that this material could be also used for solid-state barocaloric waste heat recovery [4].

[1] P. Lloveras and J.-Ll. Tamarit, MRS Ener. Sustain 8, 3 (2021).

[2] J. Li et al., Adv. Func. Mater. 31, 2105154 (2021).

[3] K. Sau et al., Sci. Rep. 11, 11915 (2021).

[4] H. Tokoro et al., Nat. Commun. 6, 7037 (2015).

13h30 - Jia Yan Law The Vast High-Entropy Alloy Space for Magnetocaloric Properties Presentation +

Place: Sala 1

High-entropy alloys (HEA) were previously focused on producing the magnetocaloric effect (MCE) at low temperatures or with subpar performance. Similar to "too many cooks spoil the soup," their multi-principal element compositions could dilute the overall magnetic moment even if the design includes ferromagnetic or rare-earth (RE) elements. A directed search strategy results in a 5-fold improvement in MCE performance without RE reliance as the HEA space extends to the second-generation region. In this talk, we will give a general overview of the magnetocaloric HEA design approach that produced this remarkable improvement, bridging the gap between HEAs and traditional MCE materials.

Acknowledgments: Work is supported by EMERGIA 2021 fellowship from Junta de la Andalucía (ref. EMC21_00418), Grant PID2019-105720RB-I00 funded by MCIN/AEI/ 10.13039/501100011033 and US Air Force Office of Scientific Research (FA8655-21-1-7044).

References:

[1] J. Y. Law, V. Franco, “Review on Magnetocaloric High-Entropy Alloys: design and analysis methods, Journal of Materials Research 38 (2023) 37 – 51.

[2] J. Y. Law, V. Franco, “Pushing the limits of magnetocaloric high entropy alloys”, APL Materials 9 (2021) 080702.

[3] J.Y. Law, et al., Acta Materialia 212 (2021) 116931.

[4] J.Y. Law, et al., Journal of Alloys and Compounds 855 (2021) 157424.

13h50 - Paulo de Faria Modelling an Active Magnetic Regenerator with Triangular Microchannel Geometry Using Indirect Experimental Measurements Presentation +

Modelling an Active Magnetic Regenerator with Triangular Microchannel Geometry Using Indirect Experimental Measurements

Place: Sala 1

Active magnetic regenerators (AMRs) are a central part of magnetic refrigerators, being responsible for generating the cooling power through the magnetocaloric effect in a cyclic way. AMRs are usually manufactured as a porous medium of packed spheres of magnetocaloric material (MCM). However, in recent years, new technologies in MCM processing and AMR manufacturing emerged, promising better hydraulic performance without reducing the heat transfer capacities and, consequently, achieving better energy performances.

With the advent of this new generation of AMRs, ordered geometries such as microchannels began to attract attention for their low friction factor, even though the exact behavior of the Nusselt number in this geometry is still uncertain, with conflicting results reported in the literature. With this in mind, the present work proposes a way of simulating AMRs with microchannel geometry using indirect experimental measurements for adjustment of an already validated AMR numerical model.

The adaptation of the numerical model consists of three fronts: (1) Pressure drop calculation, which was treated as porous media of parallel channels, (2) The heat transfer problem, which was approached with the single-blow technique for measuring the number of transfer units (NTU) of the regenerator, and (3) the demagnetization field, which was taken in to account by the demagnetization factor determined via a numerical correlation derived from results obtained from the Multiphysics software COMSOL.

For reference, a four-layer La-Fe-Si triangular microchannel AMR manufactured by Vacuumschmelze was experimentally characterized in terms of pressure drop and NTU aiming at fitting the model. The AMR cooling capacity was also determined under different operational parameters in order to use these results to validate the numerical model.

14h10 - Bikram Bhatia Barocaloric Refrigeration Device Modeling Presentation +

Place: Sala 1

Solid state refrigeration based on the barocaloric effect shows significant promise as a substitute for existing vapor compression cooling systems that have relatively low efficiency, are difficult to scale and have a high global warming potential. While recent work has focused on characterizing the caloric response of several materials, device-level studies are still missing in the literature. This work presents a thermodynamic and heat transfer model for a barocaloric refrigerator comprising commercially-available nitrile butadiene rubber (NBR) and operating between a hot and a cold thermal reservoir. We combine experimentally-validated barocaloric properties of NBR with transient heat conduction modeling to evaluate the performance of a reverse Brayton refrigeration cycle. Specifically, we evaluate the device coefficient of performance (COP) and specific cooling power, and quantify the contributions of device geometry, operating frequency, heat transfer coefficient, and applied pressure. We show that a barocaloric refrigerator operating with a 2.3 K temperature span, 10 mHz cycle frequency and 0.1 GPa applied pressure change can achieve a COP as high as 8 – exceeding that of traditional vapor compression-based refrigerators. Additionally, we show that increasing the thermal conductivity of the elastomeric solid-state refrigerant can substantially improve performance. This work demonstrates the promise of solid state cooling devices based on soft barocaloric materials and provides a framework to quantify its performance at the device-level.

14h30 Break Coffee break +

Place: Sala 1

break

14h50 - Yaroslav Mudryk Structure-property relationships in rare earth intermetallic compounds with reversible first-order transformations Presentation +

Structure-property relationships in rare earth intermetallic compounds with reversible first-order transformations

Place: Sala 1

Strong non-linear responses to external stimuli are commonly realized across first-order phase transformations. Magneto-structural or magneto-elastic transformations in solid state compounds, driven by applied magnetic field, may produce fundamentally interesting and technologically relevant phenomena, such as colossal magnetostriction or giant magnetocaloric effect. For magnetic field to be an effective thermodynamic driver, a strong coupling of magnetic and crystallographic sublattices, which exists in magnetic rare earth intermetallics, is required. First-order nature of the transition can drastically increase magnetocaloric effect but, often, it does so at the cost of hysteresis losses. Recently, R2In compounds with R = Pr, Nd, and Eu were found to exhibit nearly anhysteretic first order magnetoelastic transitions. Here we will review the basic physical behaviors of R2In compounds, discuss what distinguishes from other magnetically responsive materials, and present important open science questions that remain unanswered. We will compare their structural behaviors in the vicinity of the magnetic ordering with the behaviors of other rare earth compounds that undergo strong magneto-structural transformations, R5SixGe4-x and Nd7Pd3.

Acknowledgments: This research was performed at Ames National Laboratory and supported by the Division of Materials Science and Engineering of the Office of Basic Energy Sciences, Office of Science of the U.S. Department of Energy (DOE). Ames National Laboratory is operated for the U.S. DOE by Iowa State University of Science and Technology under Contract No. DE-AC02-07CH11358.

15h20 - Nilson A. de Oliveira A theoretical view of the entropy changes and caloric effects in solid-state materials Short course +

Place: Sala 1

The caloric effects [1-2] can be characterized by the entropy change in an isothermal process (Siso) and by the temperature change in an adiabatic process (Tad) upon variation of the external stimuli such as magnetic field, electric field, pressure, and stress. In order to perform a theoretical discussion of the caloric effects [3] in solid-state materials and calculate the key caloric quantities, it is necessary to consider the main physical ingredients to properly describe the underlying physics behind the effects.
The main goal of this talk is to introduce the basic ideas of the theoretical calculations of the caloric quantities taking into account the intrinsic features of the compound namely: the interactions between magnetic moments, crystalline electric field, spin fluctuations, magnetoelastic coupling, lattice vibrations, thermal expansion, etc. To this end, we present an overview of the theoretical models commonly used to treat the caloric effects in a series of solid-state materials. We firstly focus on the Heisenberg-like Hamiltonian, which is suitable to deal with systems whose magnetism is mainly associated with 4f-electrons which have a localized character. We present and discuss in detail the physical/mathematical procedure to calculate the thermodynamic functions of interest. In the picture of the mean-field theory, used to treat the two body interactions, we explore important aspects such as anisotropy, the nature of the magnetic phase transition, and their role in the behavior of the caloric quantities curves. Besides the magnetic degree of freedom, we also discuss the crystalline lattice and its importance to the caloric effects.
In the second step, we discuss the physical mechanism involved in the caloric properties of magnetic compounds whose magnetism comes mainly from itinerant electrons. In this case, we use a Hubbard-like Hamiltonian that better takes into account the delocalized character of the magnetic electrons. In this part, we pay attention to the charge transfer mechanism and pressure effect.
References:
[1] K. A. Gschneidner Jr, V. K. Pecharsky and A. O. Tsokol, Rep. Prog. Phys. 68, (2005) 1479.
[2] V. Franco, J. S, Blazquez, J. J. Ipus, J. Y. Law, L. M. Moreno-Ramirez, A. Conde, Progress in Mat. Science 93, (2018) 112.
[3] N. A. de Oliveira and P. J. von Ranke, Phys. Rep. 489, (2010) 89.

09h00 - João Amaral Correcting geometry effects on the MPMS®3 magnetometer Short course +

Place: Sala 1

Estimating the magnetocaloric effect via the isothermal magnetic entropy change (DeltaSM) through magnetization measurements is a frequent approach in the study of magnetic refrigerants. Naturally, any experimental errors on the estimate of magnetization will consequently lead to an error on the DeltaSM estimate.

For a given sample size and shape, together with a radial offset in relation to the magnetometer’s detection coils, there will be a geometric effect which will modify the measured magnetization value, when compared to the real magnetization of the sample. The smaller the detection coils, the larger this effect.

The MPMS®3 SQUID-VSM is currently the flagship magnetometer commercialized by Quantum Design. The device allows for fast measurements, and temperature sweeping, with 10-8 emu sensitivity. The small size of the detection coils, compared to previous generations, will lead to larger geometry effects.

In this workshop, participants will be familiarized with the Quantum Design MPMS®3 Sample Geometry Corrections software tool which can correct both DC and VSM magnetization measurements of samples with a known cylindrical, rectangular or thin film size and shape, where the radial offset of the mounting position is also known. For samples with irregular shape, and/or unknown radial offset, the combined analysis of DC and VSM measurements allows for an accurate correction of geometric effects, using the Geometry Independent Correction Method (GICM) [1]. Participants will learn how to use the GICM to correct MPMS®3 SQUID-VSM magnetization data.

References:

[1] C. O. Amorim, F. Mohseni, R. Dumas, V. S. Amaral, J. S. Amaral, “A geometry-independent moment correction method for the MPMS3 SQUID-based magnetometer”, Meas. Sci. Technol. 32 105602 (2021)

10h30 Break Coffee break +

Place: Sala 1

break

10h50 - Jaka Tušek Designing fatigue resistant elastocaloric regenerators Presentation +

Place: Sala 1

Elastocaloric cooling is being recognized as a promising alternative to vapor compression technology. It is based on the elastocaloric effect that occurs in superelastic shape memory materials. Among the various approaches to exploit the elastocaloric effect for cooling and heating, the so-called active caloric regeneration principle (analogous to the active magnetic regenerator) has shown the best performance for medium and large-scale devices to date. Recently, due to limited fatigue under tensile loading, the focus has been on compressive loading.

This presentation will outline our recent developments in designing durable and high-performance compression-loaded elastocaloric regenerators. The talk will cover a range of topics, including the thermo-hydraulic evaluation of different tube-based regenerators, the evaluation of buckling stability of elastocaloric tubes, and the cooling and heat-pumping performance of shell-and-tube-like elastocaloric regenerators. In the last part of the talk, I will focus on the challenges in designing a compact elastocaloric device with multiple regenerators that incorporates a force recovery mechanism, which is essential for efficient operation.

11h20 - Urban Tomc Towards high frequency and high-power density magnetocaloric cooling Presentation +

Place: Sala 1

Among the related technologies, magnetocaloric energy conversion represents one of the most promising alternatives to vapour compression. Despite the fact that this technology has made substantial progress over the last two decades, there are unfortunately still unsolved and strongly relevant challenges regarding the use of rare-earth materials, energy efficiency, and the competitive cost of potential future devices.

Namely, today’s state-of-the-art devices are based on the so-called Active Magnetic Regeneration, which is moderately efficient at low operating frequencies (up to 5 Hz). To achieve considerable cooling power and magnetic fields at such low frequencies, a significant amount of magnetocaloric and permanent magnet material is required, which also affects the cost. Therefore, a new research direction has emerged in recent years in which researchers are trying to develop devices that operate efficiently at much higher frequencies (up to 20 Hz or more). This would increase the power density, which in turn would allow miniaturization of the devices and the use of drastically less magnetocaloric and magnetic material. There are two major challenges to be solved. One concerns the application of new magnetic field sources that can generate a fast and efficient alternating magnetic field at high frequencies. The other one deals with the application of new thermal management principles in a form of thermal control devices. (e.g. thermal switches and diodes).

In this contribution a high-energy efficiency electro-permanent magnetic field source will be presented, which is able to oscillate relatively high magnetic fields statically and at operating frequencies up to 50 Hz with energy efficiency above 80%. Moreover, different approaches on how to tackle the issue of high-frequency heat transport will also be presented and discussed.

11h40 - Vladimir I. Zverev FeRh and its remarkable magnetocaloric properties: a fresh look Presentation +

Place: Sala 1

The review is devoted to theoretical–experimental studies of the magnetothermal properties of a family of binary and three-component alloys based on iron and rhodium. The results of calculations of properties from first principles, the self-consistent (mean) field model, empirical and ad hoc models, and numerical simulation methods are presented and analyzed. As well, numerous experimental data are presented: direct determination of the magnetocaloric effect (MCE), measurement of magnetic characteristics (field and temperature dependences of magnetization and magnetic susceptibility), measurement of temperature dependences of heat capacity, differential calorimetry, Hall magnetometry, EXAFS spectroscopy, scanning and transmission electron microscopy.

12h00 Break Coffee break +

Place: Sala 1

break

13h30 - Victorino Franco Magnetocaloric composites for fused filament fabrication Presentation +

Place: Sala 1

Additive manufacturing techniques of magnetocaloric materials are limited by the fact that melting the magnetocaloric phase has deleterious effects on the functionality of the printed parts. In fact, laser melting techniques make the active phase transform, reducing the magnetocaloric response of the sample. In this talk we present a physical method for the production of uniform polymer-based composite filaments for fused filament fabrication. The presence of functional fillers in the composite alters the transformation temperatures of the polymer and modifies the printing conditions. A comparison between the magnetocaloric response of the fillers (Heusler alloys and hydrogenated La(FeSi)13 powders) and that of the filaments and printed parts demonstrate that this printing technique does not affect the functionality of the active material.

14h00 - Yuriy Koshkid'ko Magnetocaloric Effect in Ni-Mn-In-based Heusler Alloys in High Magnetic Fields Presentation +

Place: Sala 1

NiMn- Some of the Ni-Mn-In-based Heusler alloys demonstrate an inverse magnetocaloric effect (MCE) at the magnetostructural transition (MST) temperature, TM. In this case, the values of the total entropy change (St) increase with a decrease in the difference between the temperatures of the MST and the Curie temperature (TC) of the austenitic phase (AP) [1, 2]. A study of the adiabatic temperature changes (Tad) demonstrated a similar tendency (Fig. 1) [see Ref.2].

In this work, we introduce a study of the MCE parameters and their dependence on the difference between the transition temperatures for Ni-Mn-In-based Heusler alloys with different compositions. The magnetic behaviors in magnetic fields up to 14 T, “kinetic arrest” of the ferromagnetic AP, and the results of the studies of Tad measurements using a direct method in magnetic fields up to 14 T [3] for the series of the Ni-Mn-In-based Heusler alloys are discussed in the current work.

14h20 - Pedro von Ranke Theoretical investigation of the barocaloric effect in spin-crossover systems Presentation +

Place: Sala 1

We investigated, through theoretical simulations, the barocaloric effect in spin crossover systems considering a model Hamiltonian which includes the crystalline electrical field, elastic and phonons interactions. A systematic study, through the model parameters, allowed the construction of phase diagrams showing the existence of first and second order (Low Spin (LS) High Spin (HS)) phase transition regimes. Also, the contributions of configurational, magnetic and phonons entropies, for the barocaloric effect, was investigated quantitatively. The majority contribution comes from the phonons (about 76%, in our simulation) which was associated with the large cell volume change during (LS), (HS) phase transition. In addition, our model was applied to describing the spin-crossover complex.

14h50 - Alan T. D. Nakashima Magnetic Refrigeration Technology Assessment of a Compact Wine Cooler Presentation +

Place: Sala 1

Although our physical understanding of the magnetocaloric effect and its applications has increased substantially in the past few decades, much remains to be done regarding the development and evaluation of magnetic refrigeration prototypes operating in relevant environments. In this sense, we present the results of the PoloMag project, whose aim is to develop a compact magnetic refrigeration system capable of controlling the temperature of a 31-bottle wine cooler cabinet between 8 and 20 for an ambient temperature of 25. The project was divided into two parts. The first consisted of a detailed performance comparison between a magnetic wine cooler experimental prototype and a commercial vapor-compression system which used the same insulated cabinet. The performance metrics in this assessment included the cooling capacity, power consumption and the coefficient of performance, which were used to validate a complete magnetic refrigeration system model able to accurately predict the temperature levels and power consumption of the device. The model was used in the second part of the project which aimed at upgrading the magnetic system into a fully integrated plug-and-play magnetocaloric wine cooler with efficiency levels that at least matched the conventional system. In this sense, the system model was applied in a genetic algorithmbased optimization aimed at reducing the mass of hard magnetic material, which is responsible for the largest shares of cost and potential environmental impact. In the present work, the current state of the second version of the magnetic system and its predicted thermodynamic performance will be presented. The design methodology for the second version of the cooler was built around the magnet mass minimization routine and included criteria for the efficiency and size of the magnetic cooling unit.
Keywords: Magnetic refrigerator, technology assessment, performance evaluation, wine cooler.

15h10 Break Coffee break +

Place: Sala 1

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15h30 - Mario Reis Toward all-d Hexagonal Ferromagnets Presentation +

Place: Sala 1 Full Heusler alloys display a wide range of physical phenomena with potential applications in different areas. However, there are many limiting factors to optimize their functional properties, such as poor mechanical properties. Suppression of p−d covalent hybridization has produced novel compounds, displaying enhanced mechanical properties and large caloric effects: these are the all-d Heusler alloys [1]. On the other hand, Ferromagnetic Hexagonals present similar properties as Heusler alloys, such as the occurrence of the martensitic transition, however, with much higher volume changes - just to cite one advantage. Both families of materials have multifunctional properties, with potential applications in different technological fields. Ferromagnetic Hexagonals, however, present the same brittle problem as Full Heusler, in spite of the multifunctional advantages. Very recently, we have accomplished a comprehensive review article [2]
comparing these three families regarding their mechanical ductility, caloric effects, magnetostrictive behavior and thermal regulation properties. These comprehensive analysis evidenced the similarities among these systems and allowed us to suggest further steps to obtain all-d Ferromagnetic Hexagonals by adopting successful strategies already employed to optimize Heusler compounds.

16h00 - Bruno Alho Fathoming anisotropic magnetoelasticity and magnetocaloric effect of GdNi Presentation +

Place: Sala 1 Intermetallic GdNi adopts a CrB type of crystal structure (space group Cmcm), and it orders ferromagnetically via a second-order phase transition at 70 K, exhibiting unusually strong spontaneous striction along the three independent crystallographic axes in the ferromagnetically-ordered state. We introduce a new microscopic model to describe anisotropic changes of lattice parameters and elastic contribution to magnetocaloric effect of GdNi. In the model, results of DFT calculations are used as inputs into a Hamiltonian that includes elastic energy of an anisotropic crystal lattice, exchange interactions, and Zeeman effect. The magnetic and elastic Hamiltonians are coupled through an anisotropic Bean – Rodbell model of magnetoelastic interactions. This coupling gives rise to anisotropic changes in the lattice parameters observed experimentally, and the model reveals good to reasonable agreements between the current theoretical results and earlier experimental data, thus validating the model within the limits of assumptions made.

16h20 Closing Session Award +