The attention for materials displaying high magnetocaloric effect (MCE) has grown during the past 30 years. One of the most important properties of MCE is the adiabatic temperature change ( ). The main aim of this work was to develop a method to measure the temperature change ( ) for magnetocaloric materials in a changing magnetic field.  A technique was developed where maximum reached  for Gadolinium was 1.19 K in a changing magnetic field of 1.3 T, however, this is lower value in comparison with previous studies (3.3 K in a changing magnetic field of 1 T, Bjørk, et al., 2010) which makes the developed method not sufficient enough to measure . Furthermore, finding novel materials displaying high MCE is of great interest. MnFePSiB alloys display promising MCE properties but processing method is expensive and time consuming. Therefore, a MnFePSiB compound was simply remelted several times and heat treated to enhance its properties. The MnFePSiB alloy was remelted 1, 2 and 3 times after initial casting. Melting the material 3 times resulted improvement in both the magnetic and magnetocaloric properties due to enhanced homogeneity. The material melted 3 times was further heat treated to improve its magnetic magnetocaloric properties. Heat treating the material for 5 hours at 1373K improved the magnetic entropy change more than 10 times compared to the as cast sample,  was moved closer to room temperature and maximum  of 0.71 K was obtained.

The objective of this research was to develop a novel technique for mechanical treatment to manipulate the microstructure of Nickel-Manganese-Gallium Hesuler alloys to increase anisotropy, which can lead to higher magnetocaloric properties. Ni2+xMn1-xGa intermetallics have the potential to be employed in magnetic refrigeration devices including residential refrigerators, heat pumps, and air conditioning. Solid-state magnetic refrigeration systems are smaller, quieter, and reduce energy consumption by 20% compared to existing conventional vapor-cycle refrigeration devices which rely on harmful hydro-fluorocarbon gases and pump millions of tons of greenhouse gases into the atmosphere. The magnetic refrigeration market is predicted to reach US$ 315.7 Million by 2022. Magnetic refrigeration systems can also be used in electronic systems and the space industry. The current state-of-the-art magnetic refrigeration systems use expensive rare earth elements including Gadolinuim (Gd). The need to replace Gd and other rare earth elements with cheaper and more available elements led to other alloys including Ni-Mn-Ga. By understanding the processing-microstructure-property relationship of Ni-Mn-Ga alloy, it is possible to manipulate the microstructure in order to obtain higher refrigeration capacity. It is a promising alternative to rare earth elements and improves national security by minimizing foreign dependence on the import of rare earth metals. This novel in situ study establishes that twin boundaries can be manipulated in a polycrystalline Ni-Mn-Ga alloy. This results in a change in magnetocrsytalline anisotropy, which leads to a higher magnetic cooling power. Mechanical loading in a preferred direction, traditionally referred to as a training process, was able to move the twin boundaries, and the combination of focused ion beam imaging linked specific movement with mechanical loading. This technique, in situ monitoring process, can be utilized to devise training procedures for future iterations of magnetocaloric and shape memory alloys.

La réfrigération magnétique est une technologie innovante de production de froid, qui peut remplacer la technique classique de compression-détente de fluides frigorigènes. Son principe est basé sur l'effet magnétocalorique qui se traduit par le refroidissement ou l'échauffement de certains matériaux sous l'action d'un champ magnétique. Ce travail de thèse s'est déroulé dans le cadre d'un projet « CARNOT Energies du futur » et s'oriente vers l'étude magnétothermique et fluidique de systèmes de réfrigération. Pour cela, un outil numérique a été développé à l'aide du logiciel FLUENT afin de décrire le comportement thermique de différents régénérateurs, cœur même des systèmes de RM. En parallèle, deux systèmes de réfrigération magnétique ont été développés et améliorés, chacun d'eux présentant des performances intéressantes. Ces résultats ont permis de comprendre et définir les facteurs les plus influents sur leurs performances, et en déduire ainsi leurs conditions de fonctionnement optimales / The magnetic refrigeration is an innovative technology of production of cold, which can replace the refrigerants classic compression-relaxation technique. Its principle is based on the magnetocaloric effect which leads to the cooling or the heating of certain materials under the effect of a magnetic field. This thesis work took place within the framework of a project named " CARNOT Energies of future", and turns to the magnetothermal and fluidic study of refrigeration systems. For that purpose, a digital tool was developed using the FLUENT software to describe the thermal behavior of various regenerators, heart of the MR systems. In parallel, two magnetic refrigeration systems were developed and improved, each of them bringing interesting performances. These results allowed to understand and to define the most influential factors on their performances, so as to deduct their optimal operating conditions.

No description available.

Orientador: Lisandro Pavie Cardoso / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-06T02:28:50Z (GMT). No. of bitstreams: 1 DosSantos_AdenilsonOliveira_D.pdf: 4430176 bytes, checksum: 30089a1aff00bfd64635f23601dd3039 (MD5) Previous issue date: 2006 / Resumo: Como primeira contribuição deste trabalho, as varreduras Renninger (VR) da difração múltipla de raios-X foram empregadas no estudo da transição de fase estrutural do Sal de Rochelle (monoclínica-ortorrômbica) induzida por temperatura. Devido ao caráter tridimensional e sensibilidade dessa técnica acompanhamos as deformações na célula unitária com a temperatura, através do deslocamento dos picos secundários com maior sensibilidade. Foi possível determinar os parâmetros de rede e simular cada VR com o programa UMWEG. Os picos secundários de 4-feixes ( 0 0 0 ) ( 0 0 10 )( 1 0 9 )(1 0 1 ) e (0 0 0 )( 0 0 10 )( 2 3 0 )(2 3 10 ) da fase ortorrômbica foram medidos na VR para 24ºC (Tc). Os coeficientes de expansão térmica do sal de Rochelle também foram obtidos, e estão em bom acordo com a literatura. Como segunda contribuição, usamos a VR na determinação precisa dos parâmetros de rede dos materiais magnetocalóricos PrAl2, NdAl2e PrNi5. Implementamos uma rotina baseada na simulação da VR com o programa UMWEG, através da qual escolhe-se o comprimento de onda adequado para a medida de picos secundários muito sensíveis à distorção na célula unitária. Na aplicação no caso do PrAl2 usamos o caso de 4-feixes ( 0 0 0 )( 6 0 0 )( 1 3 7 )( 7 3 7 ) com 2.... =6.663(3)º e obtivemos com grande precisão a=8,03332(7)Å. O efeito de polimento mecânico na superfície dessa amostra foi analisado pelo mapeamento das reflexões de superfície (BSD) e o comportamento mosaico do cristal foi evidenciado. Nas outras medidas, como utilizamos a mesma geometria da estação XRD1, não foi possível obter a melhor condição para a rotina apresentada, mas foram obtidos para o NdAl2 (a=7,9972(5)Å) e PrNi5 (a=4,9590(8)Å e c=3,9794(5)Å) com boa precisão. Outra contribuição foi o estudo do efeito de campo elétrico no cristal orgânico MBANP através do monitoramento por curvas de rocking da reflexão ( 10 0 0 ). Observou-se uma histerese "asa de borboleta", ainda não observada em cristais orgânicos, e sem modelo para cristais monoclínicos. Cálculos usando mecânica quântica para moléculas isoladas de MBANP mostram que as principais características da forma de histerese podem ser explicadas em termos de mudanças induzidas pelo campo elétrico nos perfis de carga e na geometria de moléculas isoladas de MBANP / Abstract: As the first contribution of this work, the Renninger scan (RS) of the X-ray multiple diffraction were used in the study of the Rochelle salt structural phase transition (monoclinic-orthorhombic) induced by temperature. Due to its three-dimensional feature and sensitivity of the technique was possible to follow the unit cell deformations with temperature, through the angular shifts of the most sensitive secondary peaks. We were able to determine the lattice parameters as well as to simulate each RS by using the UMWEG program. The ( 0 0 0 )( 0 0 10 )( 1 0 9 )(1 0 1 ) and ( 0 0 0 )( 0 0 10 )( 2 3 0 )(2 3 10 ) 4-beam peaks for the orthorhombic phase were measured in the RS at 24ºC (Tc). Rochelle salt thermal expansion coefficients were also obtained in good agreement with literature values. As the second contribution, we have also used the RS in the precise lattice parameter determination of PrAl2 , NdAl2 and PrNi5 magnetocaloric materials. We have implemented a routine based on the RS simulation (UMWEG program), through which, one can choose the adequate wavelength to measure the most sensitive secondary peaks to the unit cell variations. The application of thid method in the case of PrAl 2, has allowed to measure the ( 0 0 0 )( 6 0 0 )( 1 3 7 )( 7 3 7 ) 4- beam case that presents 2.... =6.663(3)º and hence, to determine a=8.03332(7)Å, with high precision. PrAl2surface polishing effect was also analyzed by the secondary surface peak (BSD) mapping, through which, the crystal mosaic behavior was exhibited. For the other crystals, the same LNLS geometry was used and the best condition to applying the routine could not be obtained, however good precision lattice parameters were obtained for NdAl2 (a=7.9972(5)Å) and PrNi5 (a= 4.9590(8)Å and c= 3.9794(5)Å). Another contribution to the study of the electric field application in the MBANP organic crystal through the monitoring of ( 10 0 0 ) rocking curves was performed. It was observed a (butterfly wing) hysteresis, not yet observed for organic crystals and with no model suggested for monoclinic crystals. Quantum mechanical calculations on isolated MBANP molecules show that the main features of the hysteresis shape can be explained in terms of field-induced changes in the charge profiles and geometry of isolated MBANP molecules / Doutorado / Física da Matéria Condensada / Doutor em Ciências

La réfrigération magnétique attire beaucoup d’attention ces dernières années parce qu’elle est considérée comme une technologie respectueuse de l’environnement et énergétiquement économique. Aujourd’hui, cette technologie avancée est encore en phase de recherche que des dispositifs de réfrigérations magnétiques soient déjà opérationnels. Ce travail de thèse consiste à étudier la potentialité de résistance à la corrosion de différents types de matériaux magnétocaloriques (Gd6Co1.67Si3, Ni2Mn0.75Cu0.25Ga et Pr0.66Sr0.34MnO3) en contact avec un fluide caloporteur. Afin de comprendre les propriétés magnétocaloriques des matériaux, nos recherches se sont aussi focalisées sur les relations entre la transition magnéto-structurales d’alliages Heusler Ni2Mn0.75Cu0.25Ga et (i) la distribution cationique au sein de la structure cristalline et/ou (ii) la microstructure. Finalement, le diagramme de phase magnétique et nucléaire en lien avec les effets magnétocalorique obtenu grâce à la diffraction de neutrons et de pérovskite Pr1-xSrxMnO3 (0.25≤x≤0.45) est également présenté. / Magnetic refrigeration has gained lot of importance and attention as they are highlighted to be environmental friendly, energy efficient. Presently, though at research stage, the magnetic refrigerators are pushed towards realization in domestic application with extensive work on materials and with few working models. One critical issue, the potential resistance to corrosion in case of different class of magnetocaloric materials (Gd6Co1.67Si3, Ni2Mn0.75Cu0.25Ga and Pr0.66Sr0.34MnO3) against the heat transport fluid is addressed. To better understand and improve the observed magnetocaloric properties in Heulser alloys Ni2Mn0.75Cu0.25Ga and to elaborate the same with the magneto-structural relation, studies on (i) cation distribution with in crystal structure and/or (ii) microstructural dependence are presented. Nuclear and magnetic phase diagram based on detailed neutron diffraction and magnetism studies for magnetocaloric perovskite oxide Pr1-xSrxMnO3 (0.25≤x≤0.45) is also presented

In der vorliegenden Arbeit wurden vor allem das Auftreten und der Mechanismus von feldinduzierten Übergängen und der damit verbundenen kritischen Felder untersucht. Die verwendete Magnetisierungsmessmethode ist auf die bestehende Impulsfeldanlage des IFW Dresden abgestimmt. Die Magnetisierung in Feldern bis zu 48 T wurde gemessen. Erstmals wurde für Sm2Fe17N3 der Anisotropiekoeffizient aus der Kombination der Messung des Austauschfeldes mittels inelastischer Neutronenstreuung und der Messung der Anisotropiekonstanten K1 am gleichen Material bestimmt. Für den führenden Anisotropiekoeffizienten konnte mit K1 von rund 13 MJ/m³ der Wert A20<r²> = -28 meV bestimmt werden. Der in SmCo2,5Cu2,5 und SmCo2Cu3 beobachtete Hochfeldübergang konnte mit der Mikrostruktur verknüpft werden. Die laminare Mikrostruktur bestehend aus Phasen mit unterschiedlichem Sm-Anteil ist eine notwendige Bedingung für das Auftreten des Übergangs. Das Koerzitivfeld steigt mit dem Kupfergehalt und erreicht bei tiefen Temperaturen sehr hohe Werte. Das Koerzitivfeld und das Übergangsfeld zeigen eine große magnetische Viskosität. In DyFe6Al6 wird das Verschwinden der spontanen Magnetisierung bei tiefen Temperaturen durch starke antiferromagnetische Kopplungen verursacht. Durch ein feldinduziertes magnetisches Moment an einem ungeordneten Kristallgitterplatz könnte der magnetische Übergang bei tiefen Temperaturen erklärt werden. An hexagonalem DyMn6Ge6 wurde erstmals der Temperaturverlauf des Übergangsfeldes zur gekanteten antiferromagnetischen Struktur gemessen. Oberhalb von 100 K ruft das angelegte Feld den Übergang von der helimagnetischen zu einer Fächerstruktur hervor. Bei tiefen Temperaturen tritt ein Spinflop-Übergang auf, der durch die magnetische Anisotropie des Dysprosiumions unterstützt wird. Bei magnetokalorischen Materialien zeigt sich eine Abhängigkeit der gemessenen Magnetisierung von der Feldänderungsrate. Dies lässt sich qualitativ auf die Messbedingungen zurückführen: So herrschen bei Impulsfeldmessungen adiabatische Bedingungen, während bei statischen Messungen isotherme Verhältnisse vorliegen. Neben herkömmlichen magnetischen Verbindungen wurden auch stark korrelierte Elektronensysteme untersucht. Der gefundene Magnetisierungsübergang bei 43 T in CeNi2Ge2 lässt sich auf das Unterdrücken des Kondoeffekts und das Aufbrechen der antiferromagnetischen Struktur zurückführen. Darüber hinaus wurden Magnetisierungsmessungen an Hochtemperatursupraleitern durchgeführt. Die Messungen im Impulsfeld sind ein Beitrag zur Bestimmung des Phasendiagramms von schmelztexturiertem YBa2Cu3O7-d. Das Irreversibilitätsfeld Hirr konnte an massiven Proben bis zu tiefen Temperaturen bestimmt werden. Hirr(T) zeigt einen unerwarteten linearen Anstieg bis zu tiefen Temperaturen. Aufgrund der hohen Feldänderungsraten und großen Unterschiede von Ummagnetisierungsprozessen in magnetischen Materialien gibt es derzeit keine einheitliche Beschreibung der magnetischen Viskosität für Feldänderungsraten im Bereich von 0,001 bis zu 1000 T/s. Durch die Messung im Impulsfeld konnte die Größenordnung der magnetischen Viskosität in nanokristallinem Bariumferrit bestimmt werden. Magnetisierungsmessungen im Impulsfeld stellen sowohl durch das hohe Magnetfeld als auch aufgrund der hohen bzw. variierenden Feldänderungsrate ein sehr nützliches Instrument zur Untersuchung feld- und zeitabhängiger Eigenschaften von Festkörpern dar. / In this work, the occurrence and the mechanism of field induced transitions and the related critical fields were investigated. The way of measuring the magnetisation was designed for the existing pulsed field device of the IFW Dresden. The magnetisation was measured in fields up to 48 T. For the first time, the anisotropy coefficient of Sm2Fe17N3 was obtained in the combined measurement of the exchange field via inelastic neutron scattering and the measurement of the anisotropy constant K1 for the same material. For the leading anisotropy coefficient, a value of A20<r²> = -28 meV was found using K1 of about 13 MJ/m³. It was shown that the observed high field transition in SmCo2.5Cu2.5 and SmCo2Cu3 is connected with the microstructure. The laminar microstructure consisting of phases with different Sm-content is a necessary precondition for the occurrence of the transition. The coercivity increases with the Cu-content and reaches high values at low temperature. The coercivity and the transition field show big magnetic viscosity. In DyFe6Al6, the disappearance of the spontaneous magnetisation at low temperature is caused by a strong antiferromagnetic coupling. The magnetic transition at low temperature could be explained by a field induced magnetic moment on a disordered crystal site. For the hexagonal DyMn6Ge6, the temperature dependence of the transition field towards the canted antiferromagnetic structure was measured for the first time. Above 100 K, the applied field causes the transition from the helimagnetic to the fan structure. At low temperature, a spin flop transition occurs, which is supported by the magnetic anisotropy of the Dy-ion. The magnetisation of magnetocaloric materials exhibits a dependence of the field changing rate. This can be explained qualitatively by the measurement condition: The pulsed field measurement is adiabatic, whereas during static measurements, the condition is isothermal. Besides common magnetic compounds, highly correlated electron systems were also investigated. The magnetic transition at 43 T in CeNi2Ge2 can be explained by the suppression of the Kondo effect and the breaking up of the antiferromagnetic structure. Furthermore, magnetisation of high temperature superconductors was measured. The measurements in the pulsed field are a contribution to the determination of the phase diagram of melt textured YBa2Cu3O7-d. The irreversibility field Hirr was measured for bulk samples down to low temperature. Hirr(T) shows an unexpected linear increase down to low temperature. Because of the high field-changing rates and the big differences of magnetisation processes in magnetic materials, there is no uniform description of the magnetic viscosity for field changing rates in the magnitude from 0,001 up to 1000 T/s. By the measurement in the pulsed field, the magnitude of the magnetic viscosity of nanocrystalline barium ferrite was determined. Magnetisation measurement in pulsed fields is a very useful instrument to investigate field and time dependent properties of solids due to their high magnetic field and their high and varying field changing rate.

In der vorliegenden Arbeit wurden vor allem das Auftreten und der Mechanismus von feldinduzierten Übergängen und der damit verbundenen kritischen Felder untersucht. Die verwendete Magnetisierungsmessmethode ist auf die bestehende Impulsfeldanlage des IFW Dresden abgestimmt. Die Magnetisierung in Feldern bis zu 48 T wurde gemessen. Erstmals wurde für Sm2Fe17N3 der Anisotropiekoeffizient aus der Kombination der Messung des Austauschfeldes mittels inelastischer Neutronenstreuung und der Messung der Anisotropiekonstanten K1 am gleichen Material bestimmt. Für den führenden Anisotropiekoeffizienten konnte mit K1 von rund 13 MJ/m³ der Wert A20<r²> = -28 meV bestimmt werden. Der in SmCo2,5Cu2,5 und SmCo2Cu3 beobachtete Hochfeldübergang konnte mit der Mikrostruktur verknüpft werden. Die laminare Mikrostruktur bestehend aus Phasen mit unterschiedlichem Sm-Anteil ist eine notwendige Bedingung für das Auftreten des Übergangs. Das Koerzitivfeld steigt mit dem Kupfergehalt und erreicht bei tiefen Temperaturen sehr hohe Werte. Das Koerzitivfeld und das Übergangsfeld zeigen eine große magnetische Viskosität. In DyFe6Al6 wird das Verschwinden der spontanen Magnetisierung bei tiefen Temperaturen durch starke antiferromagnetische Kopplungen verursacht. Durch ein feldinduziertes magnetisches Moment an einem ungeordneten Kristallgitterplatz könnte der magnetische Übergang bei tiefen Temperaturen erklärt werden. An hexagonalem DyMn6Ge6 wurde erstmals der Temperaturverlauf des Übergangsfeldes zur gekanteten antiferromagnetischen Struktur gemessen. Oberhalb von 100 K ruft das angelegte Feld den Übergang von der helimagnetischen zu einer Fächerstruktur hervor. Bei tiefen Temperaturen tritt ein Spinflop-Übergang auf, der durch die magnetische Anisotropie des Dysprosiumions unterstützt wird. Bei magnetokalorischen Materialien zeigt sich eine Abhängigkeit der gemessenen Magnetisierung von der Feldänderungsrate. Dies lässt sich qualitativ auf die Messbedingungen zurückführen: So herrschen bei Impulsfeldmessungen adiabatische Bedingungen, während bei statischen Messungen isotherme Verhältnisse vorliegen. Neben herkömmlichen magnetischen Verbindungen wurden auch stark korrelierte Elektronensysteme untersucht. Der gefundene Magnetisierungsübergang bei 43 T in CeNi2Ge2 lässt sich auf das Unterdrücken des Kondoeffekts und das Aufbrechen der antiferromagnetischen Struktur zurückführen. Darüber hinaus wurden Magnetisierungsmessungen an Hochtemperatursupraleitern durchgeführt. Die Messungen im Impulsfeld sind ein Beitrag zur Bestimmung des Phasendiagramms von schmelztexturiertem YBa2Cu3O7-d. Das Irreversibilitätsfeld Hirr konnte an massiven Proben bis zu tiefen Temperaturen bestimmt werden. Hirr(T) zeigt einen unerwarteten linearen Anstieg bis zu tiefen Temperaturen. Aufgrund der hohen Feldänderungsraten und großen Unterschiede von Ummagnetisierungsprozessen in magnetischen Materialien gibt es derzeit keine einheitliche Beschreibung der magnetischen Viskosität für Feldänderungsraten im Bereich von 0,001 bis zu 1000 T/s. Durch die Messung im Impulsfeld konnte die Größenordnung der magnetischen Viskosität in nanokristallinem Bariumferrit bestimmt werden. Magnetisierungsmessungen im Impulsfeld stellen sowohl durch das hohe Magnetfeld als auch aufgrund der hohen bzw. variierenden Feldänderungsrate ein sehr nützliches Instrument zur Untersuchung feld- und zeitabhängiger Eigenschaften von Festkörpern dar. / In this work, the occurrence and the mechanism of field induced transitions and the related critical fields were investigated. The way of measuring the magnetisation was designed for the existing pulsed field device of the IFW Dresden. The magnetisation was measured in fields up to 48 T. For the first time, the anisotropy coefficient of Sm2Fe17N3 was obtained in the combined measurement of the exchange field via inelastic neutron scattering and the measurement of the anisotropy constant K1 for the same material. For the leading anisotropy coefficient, a value of A20<r²> = -28 meV was found using K1 of about 13 MJ/m³. It was shown that the observed high field transition in SmCo2.5Cu2.5 and SmCo2Cu3 is connected with the microstructure. The laminar microstructure consisting of phases with different Sm-content is a necessary precondition for the occurrence of the transition. The coercivity increases with the Cu-content and reaches high values at low temperature. The coercivity and the transition field show big magnetic viscosity. In DyFe6Al6, the disappearance of the spontaneous magnetisation at low temperature is caused by a strong antiferromagnetic coupling. The magnetic transition at low temperature could be explained by a field induced magnetic moment on a disordered crystal site. For the hexagonal DyMn6Ge6, the temperature dependence of the transition field towards the canted antiferromagnetic structure was measured for the first time. Above 100 K, the applied field causes the transition from the helimagnetic to the fan structure. At low temperature, a spin flop transition occurs, which is supported by the magnetic anisotropy of the Dy-ion. The magnetisation of magnetocaloric materials exhibits a dependence of the field changing rate. This can be explained qualitatively by the measurement condition: The pulsed field measurement is adiabatic, whereas during static measurements, the condition is isothermal. Besides common magnetic compounds, highly correlated electron systems were also investigated. The magnetic transition at 43 T in CeNi2Ge2 can be explained by the suppression of the Kondo effect and the breaking up of the antiferromagnetic structure. Furthermore, magnetisation of high temperature superconductors was measured. The measurements in the pulsed field are a contribution to the determination of the phase diagram of melt textured YBa2Cu3O7-d. The irreversibility field Hirr was measured for bulk samples down to low temperature. Hirr(T) shows an unexpected linear increase down to low temperature. Because of the high field-changing rates and the big differences of magnetisation processes in magnetic materials, there is no uniform description of the magnetic viscosity for field changing rates in the magnitude from 0,001 up to 1000 T/s. By the measurement in the pulsed field, the magnitude of the magnetic viscosity of nanocrystalline barium ferrite was determined. Magnetisation measurement in pulsed fields is a very useful instrument to investigate field and time dependent properties of solids due to their high magnetic field and their high and varying field changing rate.