# Magnetocaloric Materials

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### Conferences related to Magnetocaloric Materials

2020 IEEE International Magnetic Conference (INTERMAG)

INTERMAG is the premier conference on all aspects of applied magnetism and provides a range of oral and poster presentations, invited talks and symposia, a tutorial session, and exhibits reviewing the latest developments in magnetism.

2018 19th International Conference of Young Specialists on Micro/Nanotechnologies and Electron Devices (EDM)

EDM 2018 is a significant event aimed at development of scientific schools working on foreground areas of Russian science and technology. The main areas are research, design and implementation of micro/nanostructures, radio and telecommunication devices, power electronicand mechatronic systems which are now related to the development of scientific and technological progress. The conference aims to gather young specialists of the differentuniversities of Russia, CIS and other countries. Invited Russian and foreign specialists will report about the development of science and technologies, perspectives of further development of modern electronics. This conference is focused primarily on the discussion of the fundamental theoretical and technological problems of designing and implementing products of micro- and nanoelectronics, simulation methods, and engineering experiments and physical interpretation of the results of these experiments.

TENCON 2018 - 2018 IEEE Region 10 Conference

Intelligence Outbreak, Cognitive IoT, Semiconductor Technology, Smart Energy, Smart Car, Smart City, Health Technology, Standardization, WIE, YP, Education, Exhibitions, etc

2016 IEEE Conference on Electromagnetic Field Computation (CEFC)

The aims of the IEEE CEFC are to present the latest developments in modeling and simulation methodologies for the analysis of electromagnetic fields and wave interactions, with the application emphasis being on the computer-aided design of low and high frequency devices, components and systems. Scientists and engineers worldwide are invited to submit original contributions in the conference areas. The authors are encouraged to submit a One-page Digest in the IEEE double column format. On-line submission is required and facilities are provided on the web site. The conference will feature oral and poster presentations. Authors interested in submitting their papers for review for publication in the IEEE Transactions on Magnetics are asked to submit their manuscripts in final form via the website and also bring a copy at the conference. All contributed papers will undergo peer review to determine their suitability for publication. Exhibits of commercial products will be available.

2015 25th International Crimean Conference "Microwave and Telecommunication Technology" (CriMiCo)

International Crimean Microwave Conference (CriMiCo) is held in Sevastopol, since 1991. During 24-year period it has been transformed into widely-known forum. Only in 2014 599 papers have been presented on theoretical, experimental, production and technological, application and historical aspects of microwave and telecommunication technologies. Authors of those papers are 1205 scientists and specialists from 201 universities and companies from 16 countries: Belarus, Belgium, Great Britain, Germany, Kazakhstan, China, Korea, Moldova, Netherlands, Poland, Russia, USA, Ukraine, France, Czech Republic and Japan.

### Periodicals related to Magnetocaloric Materials

Contains articles on the applications and other relevant technology. Electronic applications include analog and digital circuits employing thin films and active devices such as Josephson junctions. Power applications include magnet design as well asmotors, generators, and power transmission

Telephone, telegraphy, facsimile, and point-to-point television, by electromagnetic propagation, including radio; wire; aerial, underground, coaxial, and submarine cables; waveguides, communication satellites, and lasers; in marine, aeronautical, space and fixed station services; repeaters, radio relaying, signal storage, and regeneration; telecommunication error detection and correction; multiplexing and carrier techniques; communication switching systems; data communications; and communication theory. In addition to the above, ...

Science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage. The Transactions publishes scholarly articles of archival value as well as tutorial expositions and critical reviews of classical subjects and topics of current interest.

Synergetic integration of mechanical engineering with electronic and intelligent computer control in the design and manufacture of industrial products and processes. (4) (IEEE Guide for Authors) A primary purpose is to have an aarchival publication which will encompass both theory and practice. Papers will be published which disclose significant new knowledge needed to implement intelligent mechatronics systems, from analysis and ...

Basic and applied papers dealing both with engineering, physics, chemistry, and computer science and with biology and medicine with respect to bio-molecules and cells. The content of acceptable papers ranges from practical/clinical/environmental applications to formalized mathematical theory. TAB #73-June 2001. (Original name-IEEE Transactions on Molecular Cellular and Tissue Engineering). T-NB publishes basic and applied research papers dealing with the study ...

### Xplore Articles related to Magnetocaloric Materials

2018 IEEE International Magnetics Conference (INTERMAG), 2018

Magnetocaloric (MC) materials have the potential to renew the basis of refrigeration technologies for the next years. To date (and since first commercial devices in 1927), refrigerators operate by expansion/compression of gases in a closed circuit where the condensation/evaporation produces wasted heating/the cooling of a load. The main disadvantages of such devices are their usage of non-environmental-friendly gases (e.g. ozone ...

2006 IEEE International Magnetics Conference (INTERMAG), 2006

This article discusses the applications of magnetocaloric materials. A magnetocaloric material offers a direct, intrinsically highly efficient link between the quantum-mechanical spin system (of the electrons) and the thermal energy of the lattice. The largest heating and cooling effects are observed when the magnetization of a material strongly depends on temperature. Giant- magnetocaloric materials were recently discovered that show much ...

2017 IEEE International Magnetics Conference (INTERMAG), 2017

A big interest is attracted to the application of materials with a large magnetocaloric effect (MCE) at magnetic and magnetostructural phase transitions (PT) for creation of household refrigerators, operating near room temperature.

2015 IEEE International Magnetics Conference (INTERMAG), 2015

The problem of rate of phase transitions requires an indispensable solution, because the creation of new technologies based on “giant” effects in vicinity of phase transitions in magnetic materials is impossibly without solving of this problem. For example, the magnetocaloric effect (MCE) reaches its peaks near the phase transitions in magnetics, therefore knowledge of phase transitions rate is necessary for ...

IEEE Transactions on Magnetics, 2017

We estimate the power and efficiency of a thermal energy harvesting thermodynamic Brayton cycle using the first- and second-order magnetocaloric materials as active substance. The thermodynamic cycle was computed using a simple thermal exchange model and an equation of the state deduced from a phenomenological Landau model. For the first- and second-order materials, narrow- and high-frequency cycles are optimum and ...

### Educational Resources on Magnetocaloric Materials

#### IEEE-USA E-Books

• Magnetocaloric (MC) materials have the potential to renew the basis of refrigeration technologies for the next years. To date (and since first commercial devices in 1927), refrigerators operate by expansion/compression of gases in a closed circuit where the condensation/evaporation produces wasted heating/the cooling of a load. The main disadvantages of such devices are their usage of non-environmental-friendly gases (e.g. ozone depletion) and low energy efficiency. Conversely, magnetic refrigerator using magnetocaloric materials addresses these issues by utilizing solids of non-contaminating refrigerants and their prototypes show a larger energetic efficiency. In this case, the MC material replaces those gases and the expansion/compression is replaced by the application/removal of a magnetic field. The largest reversible temperature variation of a material submitted to a variable magnetic field in adiabatic conditions (ΔTS) occurs near the temperature of a magnetic or magnetostructural phase transition. These phase transitions can be classified as first order (FOPT) or second order ones (SOPT) according to the Ehrenfest classification. Therefore, the MC characterization is not only useful from a technological point of view but can also be used to extract information about the phase transition. It has been demonstrated that assuming a power law expression for the field dependence of the magnetic entropy change (ΔST), taking the form ΔST(T,H)=a(T)ΔHn(T ,H). The values of the exponent n at the transition temperature (Ttrans) are related with the critical exponents of a SOPT as $n= 1 +(1 -1/ \beta )/ \delta$, where the exponents β and δ give the temperature dependence of M at zero field and the field dependence of M at Ttrans, respectively. For materials with long range interactions the values of n(Ttrans} in SOPT are typically close to those using the critical exponents for mean field model (0.67). On the other hand, for short range interactions, the typical values are close to Heisenberg or 3D-Ising models (0.63 and 0.57, respectively). For the n(Ttrans) of SOPT there exists a lower limit that corresponds to the case where the material transits from a SOPT to a FOPT character, this point is called the critical point of the second order phase transition. The value at that point is 0.4 according to the critical exponents obtained from theoretical considerations. For FOPT, even if there is no critical region, the field dependence of ΔSTin the high field range leads to n values lower than 0.4. Therefore, a clear criterion exits to identify the change from SOPT to FOPT according to the values of n(Ttrans). One of the most promising families of magnetocaloric materials are LaFeSi alloys. These alloys show a magnetic FOPT that implies a large magnetocaloric response. Hydrogenation of the samples shifts the transition temperature from ≈ 200 K to temperatures close to room temperature, to facilitate their applications in devices. However, some issues have to be solved before commercialization: its cyclic stability needs to be improved and thermal hysteresis is to be minimized. Different dopants can be used to tune properties such as Ttrans, the MC response and hysteresis. In this work, we study the magnetocaloric properties of LaFeSi alloys doped with Ni (LaFe11.6-xNixSi1with x = 0, 0.1, 0.2, 0.3 and 0.4). Microstructural characterization (BSE and XRD) shows a high percentage of LaFe13phase in the alloys. EDX analysis confirms the desired nominal compositions. Magnetocaloric characterization has been performed by indirect measurements of ΔSTfrom magnetization measurements) and direct measurements of ΔTSdedicated device built in TU Darmstadt). Figure 1 shows how the temperature dependence of ΔTSis modified by the addition of Ni. The criterion to distinguish the order of the phase transition from the value of the exponent of the field dependence of ΔSThas been applied (Figure 2). This procedure allows us to estimate the composition for which the transition is in the critical point of the second-order phase transition (sample with x = 0.21), also shown in Figure 2. DFT calculations have been performed in order to explain the role of Ni atoms in LaFe13phase, showing a good agreement with experimental data.

• This article discusses the applications of magnetocaloric materials. A magnetocaloric material offers a direct, intrinsically highly efficient link between the quantum-mechanical spin system (of the electrons) and the thermal energy of the lattice. The largest heating and cooling effects are observed when the magnetization of a material strongly depends on temperature. Giant- magnetocaloric materials were recently discovered that show much larger magnetic entropy changes at elevated temperature. If the ideal magneto-caloric materials can be found, and then suitably combined with a magnet, a solenoid and a source of heat, the latter can be converted into electrical current in a simple and efficient manner.

• A big interest is attracted to the application of materials with a large magnetocaloric effect (MCE) at magnetic and magnetostructural phase transitions (PT) for creation of household refrigerators, operating near room temperature.

• The problem of rate of phase transitions requires an indispensable solution, because the creation of new technologies based on “giant” effects in vicinity of phase transitions in magnetic materials is impossibly without solving of this problem. For example, the magnetocaloric effect (MCE) reaches its peaks near the phase transitions in magnetics, therefore knowledge of phase transitions rate is necessary for creation of new technology of magnetic refrigeration at room temperature. The rate of phase transition limits the frequency of thermodynamic cycles. Accordingly, the power of refrigeration will depend on the frequency of cycles, and it is difficult to judge the profitability and competitiveness of the creation of this machine without determining the parameters of power. In this paper, we present a new technique for experimental study of the kinetics of the magnetic phase transitions under low alternating magnetic field, and the theoretical calculations of respective kinetic processes.

• We estimate the power and efficiency of a thermal energy harvesting thermodynamic Brayton cycle using the first- and second-order magnetocaloric materials as active substance. The thermodynamic cycle was computed using a simple thermal exchange model and an equation of the state deduced from a phenomenological Landau model. For the first- and second-order materials, narrow- and high-frequency cycles are optimum and give similar performances. Considering technological issues hindering the increase of frequency, we introduced a more detailed approach, where we take into account the time needed to switch the material between two heat reservoirs. We show that the first-order material equation of the state leads thermodynamic cycle shape keeping it closer to the optimum cycle. Conditions to improve the performance of the second-order materials are discussed. In addition, we infer key remarks for prototype design regarding the power density and efficiency reachable in different configurations.

• The adiabatic temperature change ΔTadand the isothermal entropy change ΔSmwere measured in a Er2Fe14B single crystal in the temperature range of 250-370 K under a magnetic field change of Δμ0H = 1.9 T. The magnetic field was applied along the crystallographic axes a and c. Under adiabatic conditions, the application of a 0.5 T field along the c-direction of the Er2Fe14B single crystal leads to a negative ΔTadat temperatures below the spin-reorientation temperature TSR= 323 K. In this case, the maximum ΔTadreaches -0.9 K in the temperature range of 270-280 K. Along the a-direction, the magnetocaloric effect above TSRis positive, and ΔTadreaches 0.68 K in the magnetic field 0.5 T at the temperatures of 320-330 K. Under isothermal conditions, the maximal magnetic entropy change is -0.86 J kg-1K-1at 328 K when the magnetic field is applied along the a-direction and ΔSm= 1.27 J kg-1K-1at 275 K if the single crystal is magnetized along the c-axis.

• Summary form only given. The use of Maxwell equations to calculate the entropy change (ΔS) in materials that have a first-order phase transition (FOPT) has been questioned as they are only valid at thermal equilibrium [1, 2]. Though, it has been recently shown that this artifact can be minimized after using appropriate protocol for the measurements [3]. The hysteresis losses and magnetocaloric effect of Ni45Co5Mn(37-x)In(13+x)alloy have been studied in this work. The ingots were prepared by vacuum arc melting technique under an argon atmosphere and were annealed at 900 C for 24 h followed by water quenching. The heating and cooling isothermal magnetizations, M(H), were measured up to 1.5 T and 5 T at a temperature range of 240 K to 338 K. During the heating process the temperature was raised from 240 K to 338 K and at each discrete temperature point, the M(H) was measured. The reverse procedure was carried in the cooling process. The area between the ascending and descending loops of the field-dependent magnetization curves of the Ni45Co5Mn37In13alloy was calculated for both heating and cooling processes at different temperatures and is shown in Fig. 1. These areas are interpreted as the magnetic hysteresis losses at different temperatures. The results reveal that under 1.5 T applied magnetic field, the heating process has significantly higher hysteresis compared to the cooling process. Both for the cooling and heating processes, the hysteresis losses are negligible up to 310 K. Though, after 314 K the hysteresis losses are considerable for the heating process, yet negligible for the cooling process. Furthermore, as shown in Fig. 1, by increasing the applied magnetic field up to 5 T, the hysteresis loss curve is shifted to the lower temperatures compared to the ones at 1.5 T. As depicted in this figure the maximum hysteresis losses at 5 T occurs at 312 K, whereas for 1.5 T the peak befalls at 318 K. By interpreting these results we can determine the temperature regions which indirect MCE measurements via Maxwell's and thermodynamic equations will produce the highest discrepancy with the direct MCE measurements. These areas are shown in Fig. 1, for the 1.5 T field (blue shaded temperature region) and the 5 T filed (red shaded temperature region). For instance, the indirect MCE measurements within 316 K to 322 K should be taken with caution for the heating process under 1.5 T. For the 5 T magnetic field this region falls within the temperature range of 307 K to 316 K. To study the magnetocaloric effect of Ni45Co5Mn(37-x)In(13+x)alloy family (x=0, 0.4) the isofield temperature-dependent magnetization curves, M(T), were derived from isothermal magnetization loops for both ascending and descending magnetic fields, and the entropy changes (ΔS) were derived and are shown in Fig. 2. This figure reveals three distinct results as follow. Firstly, for Ni45Co5Mn37In13sample, the peak of the entropy change curve under 5 T applied field occurs at 308 K in the descending curve and at 314 K in the ascending curve, whereas for the 1.5 T filed these peaks happen at 318 K and 320 K, respectively. This emphasizes the fact that the variation of the maximum applied magnetic field within same stoichiometry composition can very well change the critical temperature at which the peak of the entropy change curves occur. So when synthesizing the magnetocaloric materials, one should consider the maximum applied magnetic field in which the magnetic refrigeration system will be operational. Secondly, even a small change in the stoichiometry composition of a material can significantly change the material's critical temperatures. As shown in Fig. 2, the critical temperature of the Ni45Co5Mn36.6In13.4has been shifted by about 36 K to lower temperatures compared to the Ni45Co5Mn37In13. This suggests that material with high MCE at temperatures out of room temperature can be customized by changing their stoichiometry in order to shift their high MCE toward desirable temperatures. This is promising especially in finding suitable refrigerants for room temperature magnetic refrigeration systems. Thirdly, it is observed that the entropy change curves of Ni45Co5Mn36.6In13.4are broader than the ones for Ni45Co5Mn37In13. Relative cooling power (RCP) is given by (RCP)= ΔSM(T,H) × δTFWHM, where ΔSMis the refrigerant's isothermal magnetic entropy change and δTFWHMis the full-widthat-half-maximum of the peak of magnetic entropy. Therefore, the RCP of the Ni45Co5Mn36.6In13.4sample is higher than the one for Ni45Co5Mn37In13sample. This leads to obtaining a higher refrigeration capacity in a magnetic refrigeration system. In summary, the results of this research are very promising in synthesizing high-performance magnetocaloric materials that can be used to develop practical room temperature magnetic refrigeration systems.

• Gd5(SixGe1-x)4exhibits uniaxial magnetocrystalline anisotropy. There are few reports on direct magnetic measurements on principle and non-principal axis to determine the uniaxial nature of magnetocrystalline anisotropy. In this paper we confirm the nature of magnetocrystalline anisotropy to be uniaxial in single crystal Gd5Si2.7Ge1.3(x=0.675) sample using magnetic moment versus angle of rotation measurements. The first order magnetocrystalline anisotropy constant was also calculated on single crystal Gd5Si2.7Ge1.3(x=0.675) sample using magnetic moment versus magnetic field measurements on easy and hard axes. Effect of magnetocrystalline anisotropy on determination of the first order phase transition temperature of the sample was determined to be negligible in single crystal Gd5Si2Ge2sample using magnetic moment versus temperature measurement at various orientations of the sample.

• Gd5(SixGe1-x)4exhibits a first order phase transition for the compositions 0 <; x <; 0.575 leading to a magnetic phase transition as well. It is not possible to measure the second order phase (magnetic) transition temperatures of the individual phases with direct measurements. This is because the first order phase transition occurs before the second order phase transition. With modified Arrott plots we have shown previously that it is possible to estimate the second order phase transition of the Gd5Si4-type orthorhombic phase. In this paper we have estimated the second order phase transition temperature of the Gd5Si2Ge2-type monoclinic phase using a single crystal sample of Gd5Si1.5Ge2.5(0.375) which falls in the mixed phase region of the sample.

• Ball milling techniques have been used extensively in the last 30 years for the synthesis and processing of novel materials. The continuous fracturing and cold welding processes during milling allows to mechanically mix elements/compounds at an atomic scale, extend the solid solubility of metals and, in turn, obtain new alloys that might show interesting functional properties. In this contribution, we explored the possibility of using ball milling at different operating conditions to produce Mn-based or Ge-based alloys with attractive magnetocaloric properties. Ball milling was performed either at room temperature in argon, at liquid nitrogen temperature (cryomilling) or in a reactive hydrogen atmosphere. The as-milled powders were characterized by powder X-ray diffraction and differential scanning calorimetry. The effect of substitution of Mn for other 3d transition elements or substitution of Ge for other p-block elements is investigated with respect to the phase selection process during ball milling.