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.

Caloric materials show prospect in replacing the function of vaporcompression systems in todays cooling devices, resulting in more energy efficient cooling and eliminating the need for refrigerents which contribute to climate change. This project has focused on magnetocaloric materials, which experience changes in temperature when exposed to magnetic fields. A step to finding viable materials is developing realistic simulations. To this end, this project has investigated if the calculated magnetocaloric effect is impacted by the choice of statistic. Three systems have been studied, bcc Fe, FeRh and Fe2P, using Monte Carlo simulations. The results have shown differences in the calculated entropy change depending on the statistic of choice. The quantum statistics have shown a ∆S = 0 below the phase transition, unlike the classical statistics. At the phase tranisitions quantum statistics resulted in either similar or smaller values for the calculated change in entropy. / Kaloriska material har potential att i framtiden ersätta funktionen hos ångkomprimeringssystem i dagens kylapparater, vilket i sin tur kan leda till mer energieffektiv kylning samt eliminerar behovet av kylmedier som bidrar till klimatförändringen. I detta projekt ligger fokus på magnetokaloriska material, vilka erfar temperaturförändringar då de utsätts för magnetfält. Ett steg mot att hitta gångbara material är att utveckla realistiska simulationer. För detta ändamål undersöktes huruvida den beräknade magnetokaloriska effekten påverkas av valet av statistik. Tre system studerades, bcc Fe, FeRh samt Fe2P, med hjälp av Monte Carlo simulationer. Resultaten visade skillnader i den beräknade entropiförändringen beroende på valet av statistik. För kvantstatistiken var  ∆S = 0 för temperaturer under fasövergångerna, vilket skiljde sig från de klassiska resultaten. Vid fasövergångarna gav kvantstatistiken liknande eller mindre värden för den beräknade entropiförändringen.

No description available.

The design and development of nanoparticles is of great interest in the current energy and electronic industry. However, based on the current materials available the production cost can be high with insignificant magnetic and mechanical properties. Specifically, rare-earth magnetic materials composed of neodymium and samarium are known for their high magnetic performance, however, due to the cost of development there is a need to develop a versatile and cost effective material. Alternatively, cobalt carbide nanomaterials have shown to be a promising alternative for rare-earth free magnets as they exhibit comparable properties as hexaferrite magnetic materials. The primary goal of this dissertation focuses on the development of nanoparticles for permeant magnetic, and magnetic refrigeration applications. The first part of this work focuses on the synthesis of cobalt carbide (CoxC, x=2,3) nanoparticles using a novel polyol synthesis method by introducing a small amount of Ru, Cu, or Au as nucleating agent. It was found that the morphology and magnetic properties of the as-synthesized CoxC nanoparticles change as a result of directional growth of nanoparticles using nucleating agents. Needle-like particle morphology ranges from 20-50 nm in width and as long as 1 µm in length were synthesized using Ru as nucleating agent. These particles exhibit magnetization saturation of 33.5 emu/g with a coercivity of 2870 Oe and a maximum energy product 1.92 MGOe (BHmax) observed. Particle morphology is a critical aspect in the development of magnetic nanoparticles as anisotropic particles have shown increased coercivity and magnetic properties. These CoxC nanomaterials have a higher maximum energy product compared to previous work providing further insight into the development of non-rare earth magnetic material. The second part of this dissertation work focuses on the sol-gel synthesis of perovskite LaCaMnO3 (LCMO) nanomaterials. In this process, various chain lengths of polyethylene glycol (PEG) was added into a solution consisting of La, Ca, and Mn salts. The solution was left for the gelation process, and high temperature sintering to obtain the final product. By varying the polymer chain of the PEG, the size of the as synthesized LaCaMnO3 nanomaterials were altered. The as-synthesized LCMO nanomaterials have shown a maximum change in magnetic entropy (-ΔSM) was found to be 19.3 Jkg-1K-1 at 278 K for a field change of 0-3 T and 8.7 Jkg-1K-1 for a field change of 0-1 T. This is a significant improvement in comparison to current literature of the material suggesting that this is a promising alternative to Gd materials that is prone to oxidation. With additional development, LCMO or related maganites could lead to application in commercial technologies.

This thesis research synthesizes a new class of composite materials and investigates their properties, performance, and potential applications. The new materials that are multi-phase and multifunctional are considered for use in car cooling systems, internal combustion engine waste-heat-power generators, and engine crack healing which are major problems plaguing the auto industry. This research uses primarily experimental approaches to study the magnetocaloric compound, Ge5Si2Ge2 (GSG), that has large strain effects. Such a material was formed into a composite using Al as a substrate. The newly developed composite, GSG-Al, is the first material of its kind that possesses self-healing effects in cracks. X-ray diffraction was used to determine the crystal structures that existed within the material. It is found that the sintering process used to create the composite caused the formation of GdAlGe that is a magnetic compound with a high Curie temperature. The GSG-Al has a wide variety of crystal structures, ranging from face centered cubic for aluminum phases to monoclinic and orthorhombic phases for GSG. The discovery of GdAlGe confirmed that alpha-ThSi-type tetragonal and YAlGe-type orthorhombic crystal structures existed. Transmission electron microscopy (TEM) was used to analyze the wear debris collected during tribo-testing. The debris were also analyzed using energy-dispersive X-ray spectroscopy (EDS) for chemical analysis. The GSG-Al was put through tribological studies at several different temperatures to determine the thermal effects on the composite. The GSG-Al, although found to be ductile, showed high resistance to wear when compared to a common aluminum alloy, Al 6061-T651. The wear rate decreased with increasing temperature when the temperature was increased from the room temperature to 150 degrees C. Results showed that with GSG, the composite did not show cracking common in Al alloys. This was due to the unique thermal expansion properties of the GSG-Al. The phase transformation induced a significant volume expansion in the material and thus a giant strain effect. This research opens new approaches in energy conversion and improving efficiency of automobile engines. The composite developed here is important for future scientific investigation in the area of multifunctional materials as well as materials that exhibit self-healing tendencies.

The standard material by which all materials exhibiting magnetocaloric effect are measured is Gadnolinium. In this work we are attempting to understand how nanostructuring can impact the magnetocaloric effect, to this end we have grown Gd in various thin film structures. The samples made were grown via magnetron sputtering on MgO(100) substrates. Samples of thick Gd (2000 A) were grown and sandwiched between two layers of Cr or W and annealed at increasing temperatures to study how this can perturb the magnetic and structural properties of the Gd. Another set of samples was grown in which Gd (at various thicknesses) is in a multilayer system with W. Here the purpose is to explore how changing the thickness of the Gd can change its magnetic properties. Using the appropriate Maxwell relation, the magnetic entropy change was observed to increase with increasing annealing temperature. In a 0-4T magnetic field change, the peak entropy was found to go from approximately 1.5 J/kg-K for the unannealed sample to 4.4 J/kg-K when annealed to 600°C. The multilayers were found to all have a T C near 280 K, in contrast with what is predicted by finite size scaling. This is likely due to pinholes in the W layers allowing the Gd to act as one magnetic material.

An alternative cycle proposed for refrigeration and gas liquefaction is active magnetic regenerator (AMR) refrigeration. This technology relies on solid materials exhibiting the magnetocaloric effect, a nearly reversible temperature change induced by a magnetic field change. AMR refrigeration devices have the potential to be more efficient than those using conventional refrigeration techniques but, for this to be realized, optimum materials, regenerator design, and cycle parameters must be determined. This work focuses on the development and validation of a transient one-dimensional finite element model of an AMR test apparatus. The results of the model are validated by comparison to room temperature experiments for varying hot heat sink temperature, system pressure, and applied heat load. To demonstrate its applicability, the model is then used to predict the performance of AMRs in situations that are either time-consuming to test experimentally or not physically possible with the current test apparatus.

A technology with the potential to create efficient and compact refrigeration devices is an active magnetic regenerative refrigerator (AMRR). AMRRs exploit the magnetocaloric effect displayed by magnetic materials whereby a reversible temperature change is induced when the material is exposed to a change in applied magnetic field. By using the magnetic materials in a regenerator as the heat storage medium and as the means of work input, one creates an active magnetic regenerator (AMR). Although several laboratory devices have been developed, no design has yet demonstrated the performance, reliability, and cost needed to compete with traditional vapor compression refrigerators. There are many reasons for this and questions remain as to the actual potential of the technology. The objective of the work described in this thesis is to quantify the actual and potential performance of a permanent magnet AMR system. A specific device configuration known as a dual-nested-Halbach system is studied in detail. A laboratory scale device is created and characterized over a wide range of operating parameters. A numerical model of the device is created and validated against experimental data. The resulting model is used to create a cost-minimization tool to analyze the conditions needed to achieve specified cost and efficiency targets. Experimental results include cooling power, temperature span, pumping power and work input. Although the magnetocaloric effect of gadolinium is small, temperature spans up to 30 K are obtained. Analysis of power input shows that the inherent magnetic work is a small fraction of the total work input confirming the assumption that potential cycle efficiencies can be large. Optimization of the device generates a number of areas for improvement and specific results depend upon targeted temperature spans and cooling powers. A competitive cost of cooling from a dual-nested-Halbach configuration is challenging and will depend on the ability to create regenerator matrices with near-ideal adiabatic temperature change scaling as a function of temperature. / Graduate / 0548 / 0791 / 0607 / atura@uvic.ca

An alternative cycle proposed for refrigeration and gas liquefaction is active magnetic regenerator (AMR) refrigeration. This technology relies on solid materials exhibiting the magnetocaloric effect, a nearly reversible temperature change induced by a magnetic field change. AMR refrigeration devices have the potential to be more efficient than those using conventional refrigeration techniques but, for this to be realized, optimum materials, regenerator design, and cycle parameters must be determined. This work focuses on the development and validation of a transient one-dimensional finite element model of an AMR test apparatus. The results of the model are validated by comparison to room temperature experiments for varying hot heat sink temperature, system pressure, and applied heat load. To demonstrate its applicability, the model is then used to predict the performance of AMRs in situations that are either time-consuming to test experimentally or not physically possible with the current test apparatus.

Magnetic, magnetocaloric, magnetotransport and magnetoelastic properties of Ni-Mn-X (X = In, and Ga) Heusler alloys and La-Fe-Si based rare earth compounds have been synthesized and investigated by x-ray diffraction, magnetization, strain, and electrical resistivity measurements. The phase transitions, magnetic, magnetocaloric, magnetotransport and magnetoelastic properties strongly depend on the composition of these systems. In Ni50Mn50-xInx with x = 13.5, magnetocaloric and magnetotransport properties associated with the paramagnetic martensitic to paramagnetic austenitic transformation were studied. It was shown that magnetic entropy changes (SM) and magnetoresistance (MR) associated with this transformation are larger and the hysteresis effect is significantly lower when compared to that associated with paramagnetic-ferromagnetic transitions or ferromagnetic-antiferromagnetic/paramagnetic transitions in other systems. The Hall resistivity and the Hall angle shows unusual behavior in the vicinity of the martensitic phase transition for Ni50Mn50-xInx with x = 15.2. The observed Hall resistivity and Hall angle are 50 μ*cm and , respectively. It was observed that the presence of Ge, Al and Si atoms on the In sites strongly affects the crystal structure, and the electric and magnetic behaviors of Ni50Mn35In15. It was found that the partial substitution of In atoms by Si in Ni50Mn35In15 results in an increase in the magnetocaloric effect, exchange bias and shape memory effect. In Ni50Mn35In15-xSix, the peak values of positive SM for magnetic field changes H = 5 T were found to depend on composition and vary from 82 Jkg-1K-1 for x = 1 (at T = 275 K) to 124 Jkg-1K-1 for x = 3 (at T = 239 K). The partial substitution of Ni by Co in Ni50Mn35In15 significantly improves the magnetocaloric effect and MR in the vicinity of martensitic transition. In addition, significantly large inverse SM and MR were observed at the inverse martensitic phase transitions of the Ga-based magnetic shape memory Heusler alloys Ni50-xCoxMn32-yFeyGa18. The phase transition temperatures and magnetic properties were found to be correlated with the degree of tetragonal distortion in these samples. In LaFe11.57Si1.43Bx the crystal cell parameters and Curie temperatures were found to increase linearly with increasing B concentration up to ~ 0.1 % and 9 %, respectively. It was found that the characteristics of the magnetocaloric effect of LaFe11.57Si1.43 can be adjusted by a change in B concentration in the LaFe11.57Si1.43Bx system. A study of the influence of a small substitution of Ni, Cu, Cr, and V for Fe in LaFe11.4Si1.6 revealed that the magnetic, magnetocaloric, and magnetovolume coupling constant is related to an increase in the average Fe-Fe interatomic distances, leading to a change in the d-d exchange interaction.