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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Magnetocaloric Effect and Critical Behavior Investigations in La{sub 0.45}Pr{sub 0.2}Sr{sub 0.35}MnO{sub 3} Manganite Oxide

Structural, magnetic, and magnetocaloric effect (MCE) properties and the critical behavior of the La{sub 0.45}Pr{sub 0.2}Sr{sub 0.35}MnO{sub 3} sample prepared by the sol–gel method have been investigated. The X-ray diffraction characterization reveals that our sample crystallizes in the orthorhombic structure with Pnma space group. Magnetization versus temperature measurement shows that our compound exhibits a ferromagnetic–paramagnetic transition. The Curie temperature is found to be 348 K. Close to this temperature, the maximum values of the magnetic entropy change (ΔS{sub M}) and the relative cooling power (RCP) are found to be 2.84 J/kg/K and 230 J/K under µ{sub 0}H = 5 T, respectively. The Arrott plots revealed that this compound exhibits a second-order magnetic phase transition at T{sub C}. The critical behavior has been investigated by several techniques which are the modified Arrott plot method, the Kouvel–Fisher method, and the critical isotherm analysis. The obtained critical exponents β, γ, and δ are consistent with those predictions of the mean-field model. Their reliability was confirmed by Widom’s scaling relation, as well as the universal scaling hypothesis.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Magnetic, Magnetocaloric Properties, and Phenomenological Model in Amorphous Ni{sub 80−x}Fe{sub x}(SiB){sub 20} Alloys with (x = 0, 2.4, 8, and 16)

Amorphous Ni{sub 80−x}Fe{sub x}(SiB){sub 20} ribbons with different Fe concentrations (0 ≤ x ≤ 16) were fabricated by melt spinning technique, and their magnetic and magnetocaloric properties were investigated and a phenomenological model was also applied. The Curie temperature (T{sub C}), magnetic moment of transition metal and maximum magnetic entropy change (− ΔS{sub M}) increase with increasing Fe content. At a magnetic field change of 2 T, the (− ΔS{sub M}) and relative cooling power (RCP) show the highest values of 0.53 J/kg K and 85 J kg{sup −1} respectively for Fe{sub 16}Ni{sub 64}(SiB){sub 20} alloys. In addition, a satisfactory agreement between the experimental and Hamad’s phenomenological model is reported.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structural Analysis, Magnetocaloric Effect, and Critical Exponents for La{sub 0.6}Sr{sub 0.2}Na{sub 0.2}MnO{sub 3} Manganite

This work focuses on the structural, magnetocaloric effect, and critical exponent investigations of La{sub 0.6}Sr{sub 0.2}Na{sub 0.2}MnO{sub 3} manganite prepared via sol–gel method. XRD analysis confirms the rhombohedral structure with R 3-bar c symmetry for this sample, and Rietveld method was used to estimate its different structural parameters. The sample presents FM-PM phase transition of second-order type at T{sub C} = 309 K. The maximum of magnetic entropy change (−ΔS{sub M}{sup max}) and relative cooling power (RCP) reach values of about 3.57 J kg{sup −1} K{sup −1} and 214.46 J kg{sup −1}, respectively (at μ{sub 0}H = 5 T). These values indicate that La{sub 0.6}Sr{sub 0.2}Na{sub 0.2}MnO{sub 3} sample can be used as active magnetic refrigerator. Critical exponents (β, γ, and δ) of the sample have studied by analyzing the M(μ{sub 0}H, T) isotherms using different techniques. The estimated values of these critical exponents are found to be different to those predicted for standard theoretical models.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Phase Diagram and Magnetocaloric Effect of Mn{sub 2}Tb-Fe{sub 2}Tb System

Mn{sub 2}Tb-Fe{sub 2}Tb phase diagram was drawn, and the crystal structure and magnetocaloric effect of (Mn{sub 1-x}Fe{sub x}){sub 2}Tb (x ≤ 0.5) compounds at the Mn-rich side were systematically studied. X-ray diffraction demonstrates that all these Laves phase compounds crystallize in the cubic MgCu{sub 2}-type structure. The Rietveld results of XRD shows the cell volume increases with Fe content. The influence of doping effect in (Mn{sub 1-x}Fe{sub x}){sub 2}Tb (x ≤ 0.5) compounds on their magnetic and magnetocaloric properties for all solid solutions is presented. The Curie temperature (Tc) rises from 49 K (for x = 0.0) to 322 K (for x = 0.5), depending on Fe content significantly. Based on Landau’s theory, the magnetization behavior and magnetic transition were analyzed. The magnetocaloric effect (MCE) of (Mn{sub 1-x}Fe{sub x}){sub 2}Tb compounds is also discussed using the Maxwell relation, and the maximum magnetic entropy change (− ΔS{sub M}{sup Max}) approaches to 10 J kg{sup −1} K{sup −1} at x = 0 under a field ranging from 0 to 5 T. The best relative cooling power (RCP) reaches 535.03 J/kg (x = 0.1).

36 MATERIALS SCIENCE↗
DOE OSTI2019

Impact of Titanium Doping on Structural, Magnetic, and Magnetocaloric Properties and Order of Transition in La{sub 0.5}Pr{sub 0.3}Ba{sub 0.2}Mn{sub 1-x}Ti{sub x}O{sub 3} (x = 0.0 and 0.1) Manganite

In this paper, we study the structural, magnetic, and magnetocaloric properties of the polycrystalline peroviskite manganites La{sub 0.5}Pr{sub 0.3}Ba{sub 0.2}Mn{sub 1-x}Ti{sub x}O{sub 3} with x = 0 and 0.1. Our samples were prepared by solid-state reaction method. The XRD study has been analyzed by Rietveld refinement technique. Both samples crystallize in the rhombohedral symmetry with R 3-bar c space group. The second order of magnetic phase transition in all samples is confirmed by the Arrott analysis and the behavior of the master curve. Moreover, the magnetic entropy change ∆S{sub M} has been determined by the Maxwell relation, using phenomenological model and Landau theory. The relative cooling power (RCP) value under a magnetic field of 5 T is 236.29 J kg{sup −1} for La{sub 0.5}Pr{sub 0.3}Ba{sub 0.2}Mn{sub 0.9}Ti{sub 0.1}O{sub 3} sample which will be an interesting compound for application materials. Also, an agreement was found between the magnetic entropy change values calculated by Landau theory and those obtained using Maxwell relation above T{sub C} and a difference below it, for a magnetic field of 2 T.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Forecasting Peak Electricity Demand for Los Angeles Considering Higher Air Temperatures due to Climate Change

We report that Los Angeles County (LAC) is a large urbanized region with 9.7 million residents (as of 2010) and aging infrastructure. Population forecasts indicate that LAC will become home to an additional 1.2-3.1 million residents through 2060. Additionally, climate forecasts based upon representative concentration pathway (RCP) scenarios 4.5 and 8.5 indicate that average air temperatures will increase by 1-4 degrees C (2-7 degrees F) in the region. Both of these factors are expected to result in higher summertime peak electricity demand due to growth in the number of buildings, the percentage of installed air conditioners (ACs), and the additional cooling load on those air conditioners. In order to understand potential power reliability issues, and support infrastructure planning efforts, a long-term peak demand forecast was developed using hourly residential and commercial (R&C) building energy models. Peak hour electricity demand was estimated to increase from 9.5 to 12.8 GW for R&C sectors, to 13.0-17.3 GW (2-36%) and 14.7-19.2 GW (16-51%) by 2060 for the population forecasts from the California Department of Finance and the Southern California Association of Governments respectively. While marginal increases in ambient air temperature due to climate change accounted for only 4-8% of future increases in peak demand, differences in annual maximum temperatures within the 20-year periods affected results by 40-66% indicating a high sensitivity to heat waves. Population growth of at least 1 million people is anticipated to occur mostly in the northern cities of Palmdale, Lancaster, and Santa Clarita, bringing an additional 0.4-1 GW of peak demand in those regions. Building and AC efficiency are anticipated to improve as national and state efficiency standards increase, and as older, less efficient units are replaced; this could offset some of the projected increases in peak demand. Furthermore, development of shared wall, multi-family dwelling units could enable population growth of up to 3 million people without increasing peak demand.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2016

Changes in future air quality, deposition, and aerosol-cloud interactions under future climate and emission scenarios

The prospect of global climate change will have wide scale impacts, such as ecological stress and human health hazards. One aspect of concern is future changes in air quality that will result from changes in both meteorological forcing and air pollutant emissions. In this study, the GU-WRF/Chem model is employed to simulate the impact of changing climate and emissions following the IPCC AR4 SRES A1B scenario. An average of 4 future years (2020, 2030, 2040, and 2050) is compared against an average of 2 current years (2001 and 2010). Under this scenario, by the Mid-21st century global air quality is projected to degrade with a global average increase of 2.5 ppb in the maximum 8-hr O 3 level and of 0.3 mg m 3 in 24-hr average PM2.5. However, PM2.5 changes are more regional due to regional variations in primary aerosol emissions and emissions of gaseous precursor for secondary PM2.5. Increasing NOx emissions in this scenario combines with a wetter climate elevating levels of OH, HO 2 , H 2 O 2 , and the nitrate radical and increasing the atmosphere’s near surface oxidation state. This differs from findings under the RCP scenarios that experience declines in OH from reduced NOx emissions, stratospheric recovery of O 3 , and increases in CH 4 and VOCs. Increasing NO x and O 3 levels enhances the nitrogen and O 3 deposition, indicating potentially enhanced crop damage and ecosystem stress under this scenario. The enhanced global aerosol level results in enhancements in aerosol optical depth, cloud droplet number concentration, and cloud optical thickness. This leads to dimming at the Earth’s surface with a global average reduction in shortwave radiation of 1.2 W m 2 . This enhanced dimming leads to a more moderate warming trend and different trends in radiation than those found in NCAR’s CCSM simulation, which does not include the advanced chemistry and aerosol treatment of GU-WRF/Chem and cannot simulate the impacts of changing climate and emissions with the same level of detailed treatments. This study indicates that effective climate mitigation and emission control strategies are needed to prevent future health impact and ecosystem stress. Further, studies that are used to develop these strategies should use fully coupled models with sophisticated chemical and aerosol-interaction treatments that can provide a more realistic representation of the atmosphere.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Climate-driven trends of biogenic volatile organic compound emissions and their impacts on summertime ozone and secondary organic aerosol in China in the 2050s

As a precursor of ozone (03) and secondaty organic aerosol (SOA), volatile organic compounds (VOCs) largely derive from natural sources, which may va1y with future climate change patterns. In this study, the emissions and impacts of biogenic VOCs (BVOCs) were projected into summertime of the 2050s (average for 2048-2052) for China using the Model of Emissions of Gases and Aerosols from Nature (MEGAN) and the Community Multiscale Air Quality Model (CMAQ) driven by future meteorological fields simulated with the Weather Research and Forecasting Model (WRF) for two future climate scenarios (RCP4.5 and RCP8.5). Sutface temperatures were projected to increase by 0.18 K yr 1 and 0.34 K yr 1 under RCP4.5 and RCP8.5, respectively. Such increases in future surface temperatures will increase BVOC emissions, as emissions of isoprene and monoterpene (ac­counting for 77.73% of all BVOCs in China at the current time) are projected to increase by 11.13% and 25.20% under the two RCP scenarios in the 2050s, respectively. Consequently, such increases in BVOCs will also have considerable impacts on concentrations of 03 and SOA. BVOCs contribute 10.11% of 03 and 62.59% of SOA concentrations in eastern China at current time. Under the RCP8.5 scenario, climate-driven BVOC changes will enhance 03 and SOA concentrations by 0.90% and 7.33% in eastern China from ClUTent to the 2050s and account for 31.83% and 52.80% of total 03 and SOA changes, respectively, on average across five typical regions. Such increases in 03 and SOA concentrations resulting from climate-driven BVOC changes decline considerably under the RCP4.5 scenario to less than 0.80% and 6.50%, respectively, implying that climate mitigation can facilitate air pollution control by alleviating an increase in BVOCs.

Liu, Song↗
DOE OSTI2022

How will United States commercial building energy use be impacted by IPCC climate scenarios?

Climate change and anthropogenically-forced shift of weather in the future will impact energy use and resilience of both the built environment and the electric grid. The aim of this analysis is to understand how future climate scenarios will impact electricity and natural gas use of commercial buildings in the United States. Here, this study analyzes this impact for 2030, 2045, and 2100 using Representative Concentration Pathways (RCP) scenarios defined in Intergovernmental Panel on Climate Change (IPCC) Assessment Report 5. The large, gridded simulation of meteorological variables for RCPs 2.6, 4.5, 6.0, and 8.5 are selected and downscaled to make available hourly Future Meteorological Year (FMY) weather files for use and improvement in subsequent studies. High performance computing resources use these FMYs to simulate commercial prototype buildings in every American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) climate zone of the United States (US), and results are scaled to nation-wide energy use using conditioned floor area multipliers. The analysis is conducted without speculating the physical and performance traits of future buildings or the grid characteristics. This analysis quantifies the impact of climate change on source electrical and natural gas usage for commercial buildings in the United States over the next 80 years. If US commercial floorspace remained constant, total energy use by 2100 is predicted between an 1.75% decrease under the greatest emission scenario (8.5) and a 1.76% increase under the lowest emission scenario (2.6). When adjusted for anticipated urban growth by 2100, the predicted range is 65% increase (8.5) and 71% increase (2.6). Under a global temperature rise climate scenario, the warmest US climate zones will see a large increases in electricity use derived from space cooling while the coldest US climate zones will see significant decreases in natural gas use caused by the decrease in heating necessary. While climate change may ultimately require adaptations of the built environment to withstand its effects and because the United States is a country that requires more heating than cooling, from a building energy perspective, climate change (average temperature rise) is a net energy saver for the United States.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

Projection of temperature-related mortality due to cardiovascular disease in beijing under different climate change, population, and adaptation scenarios

Highlights: • The population change can bring 5 times growth to temperature-related CVD deaths. • Increase of heat-related CVD deaths is higher than decrease of cold-related ones. • The adaptation to climate change may cause more temperature-related CVD deaths. Human health faces unprecedented challenges caused by climate change. Thus, studies of the effect of temperature change on total mortality have been conducted in numerous countries. However, few of those studies focused on temperature-related mortality due to cardiovascular disease (CVD) or considered future population changes and adaptation to climate change. We present herein a projection of temperature-related mortality due to CVD under different climate change, population, and adaptation scenarios in Beijing, a megacity in China. To this end, 19 global circulation models (GCMs), 3 representative concentration pathways (RCPs), 3 socioeconomic pathways, together with generalized linear models and distributed lag non-linear models, were used to project future temperature-related CVD mortality during periods centered around the years 2050 and 2070. The number of temperature-related CVD deaths in Beijing is projected to increase by 3.5–10.2% under different RCP scenarios compared with that during the baseline period. Using the same GCM, the future daily maximum temperatures projected using the RCP2.6, RCP4.5, and RCP8.5 scenarios showed a gradually increasing trend. When population change is considered, the annual rate of increase in temperature-related CVD deaths was up to fivefold greater than that under no-population-change scenarios. The decrease in the number of cold-related deaths did not compensate for the increase in that of heat-related deaths, leading to a general increase in the number of temperature-related deaths due to CVD in Beijing. In addition, adaptation to climate change may enhance rather than ameliorate the effect of climate change, as the increase in cold-related CVD mortality greater than the decrease in heat-related CVD mortality in the adaptation scenarios will result in an increase in the total number of temperature-related CVD mortalities.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Magnetocaloric response with significant mechanical efficiency in frustrated intermetallic compound $\mathrm{Pr_{2}Co_{0.86}Si_{2.88}}$

We report magnetically frustrated materials are considered as a promising unconventional members of caloric materials. Here, the magnetocaloric properties of the frustrated Pr 2 Co 0.86 Si 2.88 have been investigated and discussed with the aid of density functional theory (DFT) calculations. The material exhibits a magnetic entropy change (-ΔS M ) of 13.1 J/kg-K for ΔH = 70 kOe around low-temperature transition T L ~ 4 K associated with the antiferromagnetic coupling between localized Pr-4f and itinerant Co-3d moments. Despite the absence of any long-range magnetic order, the obtained - ΔS M is one of the highest among the known Pr-based good magnetocaloric materials at cryogenic temperature range. It also exhibits a relative cooling power (RCP) of ~ 201 J/kg and an adiabatic temperature change of 6.3 K around T L at 70 kOe. Moreover, the compound also exhibits a high mechanical efficiency and moderate electrical efficiency, being beneficial for possible technological applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Magnetic and magnetocaloric properties of DyCo 2 C x alloys

The magnetic and magnetocaloric properties of DyCo 2 C x (x = 0, 0.05, 0.1, and 0.15) alloys were investigated. The results show that the Curie temperature (T C ) of the DyCo 2 C x alloys increases with increasing C content, from 136 K (x = 0) to 152 K (x = 0.15), but the lattice parameter a of DyCo 2 C x exhibits a maximum at x = 0.05. The suppression of the ac susceptibility of DyCo 2 C x at low temperature indicates the enhancement of the domain wall pinning effect by carbon doping. The positive slops of the Arrott plots of the doped compounds indicate that the phase transition is second order for the carbon-doped alloys, and the maximum value of the isothermal magnetic entropy change (ΔS M ) for the magnetic field change of 50 kOe decreases from -13.9 J/kg· K (x = 0) to -7.8 J/kg·K (x = 0.15). Lastly, the relative cooling power (RCP) of DyCo 2 C x is nearly the same in all studied alloys, while the temperature-averaged entropy change over 10 K temperature span, TEC(10), indicates decreasing magnetocaloric performance of carbon doped materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Impacts of climate change on future hurricane induced rainfall and flooding in a coastal watershed: A case study on Hurricane Harvey

The warming climate is likely to increase hurricane-associated extreme rainfall and lead to sea-level rise (SLR). Thus, how the floods induced by intense hurricanes respond to these potential changes is of great concern. This study investigates the future warmer climate impacts on hurricane-induced extreme rainfall, and—more importantly—the subsequent compound flooding at the watershed scale (from an event-based analysis perspective). To this goal, a modeling framework is designed based on the Distributed Hydrology Soil Vegetation Model (DHSVM), the Two-Dimensional fvand the Regional Community Earth System Model (R-CESM). The framework was applied to Hurricane Harvey (2017) at the Clear Creek watershed (a coastal watershed in the southern Houston) as a case study. The results show that the projected maximum rainfall totals over the watershed would be exacerbated by 17.7 % and 49.7 % in the 2050s and 2090s (respectively) under Representative Concentration Pathway 8.5 (RCP 8.5). This means a 16.1 % increase in Harvey rainfall over the watershed per degree Celsius increase in Mean Surface Temperature over the Gulf of Mexico region (18°~31° N, 77°~98° W). Meanwhile, the increases in maximum inundation extent would be 11.0 % (2050s) and 19.5 % (2090s). Furthermore, considerable increases in maximum inundation depth and duration in regions along the middle and downstream of Clear Creek (and also those around Clear Lake) are expected. The projected SLR will have little effect on the maximum inundation depth and extent if storm surge changes are not taken into account; meanwhile, it will influence the inundation duration at downstream locations. In conclusion, this modeling framework can be also applied at other coastal watersheds to evaluate the projected climate change impacts on the compound flooding induced by extreme climate events.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

The effect of boron doping on crystal structure, magnetic properties and magnetocaloric effect of DyCo 2

In this study, the magnetic properties and magnetic entropy changes of DyCo 2 B x (x=0, 0.05, 0.1, and 0.2) alloys were investigated. The Curie temperature (TC) increases with increasing B concentration. The frequency dependence of ac magnetic susceptibility of DyCo 2 caused by the narrow domain wall pinning effect is depressed by B doping, but the coercivity and the magnetic viscosity are prominently increased in the B doped alloys. The magnetic transition nature of DyCo 2 B x changes from the first-order to the second-order with increasing x, which leads to the decrease of the maximum magnetic entropy change. However, the relative cooling power (RCP) of DyCo 2 and the B doped alloys remains nearly constant.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Magnetic and magnetocaloric properties of Gd 1 - x Y x 2 NiSi 3 compounds (x = 0.25, 0.5, 0.75)

Here, we report the magnetic dilution effect on the magnetic and magnetocaloric properties of Gd 1 - x Y x 2 NiSi 3 (x = 0.25, 0.5, 0.75) compounds by partial substitution of Y ions in Gd 2 NiSi 3 . The X-ray diffraction studies indicate all theses compounds form in AlB 2 type hexagonal crystal structure. The dc magnetic measurements reveal the compounds undergo antiferromagnetic like phase transition below 11.5, 7.2, and 3.1 K for x = 0.25, 0.5 and 0.75 compositions, respectively. The magnetic ground state of the compounds becoming increasingly fragile with the increase in Y concentration, and results in magnetic field induced ferromagnetic transition. Such change in magnetic spin configuration is responsible for moderately large magnetic entropy change (ΔS M ~ 19.3 J/kg-K, 14.8 J/kg-K and 9.8 J/kg-K for (x = 0.25, 0.5, 0.75), respectively, for ΔH = 7T) in the cryogenic temperature region. The relative cooling power (RCP) has also been measured for all the compounds that appears to be modest (~503 J/kg for 7T magnetic field change) for x = 0.25 analogue and reduces further with magnetic dilution effect caused by Y substitution.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Behavior of the magnetocaloric effect and critical exponents in La{sub 0.67}Sr{sub 0.33}Mn{sub 1−x}V{sub x}O{sub 3} manganite oxide

We have investigated the magnetocaloric effect along with magnetic phase transition and critical exponent analysis in mixed manganite La{sub 0.67}Sr{sub 0.33}Mn{sub 1−x}V{sub x}O{sub 3} (0≤x≤0.15). To determine the nature of the paramagnetic to ferromagnetic phase transition, found to be of second-order, we performed a critical exponents study by dc-magnetization M(H,T) measurements around the Curie temperature T{sub C}. Modified Arrott plot method has been adopted to study the critical behavior of the compounds at their transition region, the values of critical exponents β, γ and δ are close to those expected for three-dimensional Heisenberg class with short-range interaction. A large magnetic entropy change |ΔS{sub M}| deduced from isothermal magnetization curves, has been observed in our samples with a peak centered on their respective T{sub C}. With increase in vanadium content, the temperature corresponding to the maximum entropy change as well as the magnetic transition temperature gradually shifts to low temperatures. The field dependence of the magnetic entropy change is also analyzed, which shows the power law dependence namely, ΔS{sub M}∝H{sup n}. Relative cooling power increases from 205 J/kg for x=0.00 to 258 J/Kg for x=0.15 making these materials a promising candidates for magnetic refrigeration near room temperature. - Graphical abstract: Scaling plot below and above T{sub C} using the β and γ exponents determined from the Arrot plot method of La{sub 0.67}Sr{sub 0.33}Mn{sub 1−x}V{sub x}O{sub 3} for x=0.15. - Highlights: • The paramagnetic to ferromagnetic phase transition of La{sub 0.67}Sr{sub 0.33}Mn{sub 1−x}V{sub x}O{sub 3} (0≤x≤0.15) is found to be of second-order. • The field dependence of the magnetic entropy shows the power law dependence namely, ΔS{sub M}∝H{sup n}. • Moderate values of −ΔS{sub M}{sup max} and RCP make the La{sub 0.67}Sr{sub 0.33}Mn{sub 1−x}V{sub x}O{sub 3} compounds potential candidates for magnetic refrigeration applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Enhancement of magnetocaloric properties in (1 − x)La{sub 0.7}Ca{sub 0.2}Sr{sub 0.1}MnO{sub 3}/xLa{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}MnO{sub 3} composite system (0 ≤ x ≤ 1)

Highlights: • The parent compounds were elaborated by solid-state reaction. • Continuous curves were investigated by the numerical calculations in (1 − x)La{sub 0.7}Ca{sub 0.2}Sr{sub 0.1}MnO{sub 3}/xLa{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}MnO{sub 3} system. • The optimum magnetocaloric effect has been found for the composition with x = 0.45. - Abstract: The present work reveals an especial agreement between the experimental results and the continuous curves investigated by the numerical calculations in (1 − x)La{sub 0.7}Ca{sub 0.2}Sr{sub 0.1}MnO{sub 3}/xLa{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}MnO{sub 3} composite system. Moreover, the ability to adjust the magnetic entropy change in a large temperature range is revealed to be possible by the mixture of both individual phases La{sub 0.7}Ca{sub 0.2}Sr{sub 0.1}MnO{sub 3} and La{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}MnO{sub 3}. Our samples have been synthesised using the solid state method. Rietveld refinements of the X-ray diffraction patterns show that both samples are single phase. The Curie temperature T{sub C} is found to be 308 K and 338 K for La{sub 0.7}Ca{sub 0.2}Sr{sub 0.1}MnO{sub 3} and La{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}MnO{sub 3}, respectively. Moreover, the magnetic entropy change and the Relative Cooling Power (RCP) values were estimated. We have shown that the optimum magnetocaloric effect at μ{sub 0}H = 2T has been found for the composition with x = 0.45, which exhibits a table-like ΔS curve with a peak value slightly lowered and strongly expanded when comparing with the parent compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Structural, electronic, magnetic, and magnetocaloric properties in metallic antiperovskite compound Mn3GaC

Highlights: • We have studied the magnetocaloric effect of the metallic antiperovskite compound Mn{sub 3}GaC. • We used the ab-initio calculations, the Monte Carlo simulations and mean field theory. • A second-order ferromagnetic-paramagnetic phase transition about T{sub C} ∼ 249 K. • The magnetic moment and the exchange coupling interactions are calculated. - Abstract: The structural, electronic, magnetic, and magnetocaloric properties of the metallic antiperovskite compound Mn{sub 3}GaC were investigated using several theoretical methods such as: First principle calculations, Monte Carlo simulations and mean field theory. The metallic antiperovskite compound Mn{sub 3}GaC exhibits a second-order ferromagnetic-paramagnetic phase transition around T{sub C} = 249 K. Using the first principle calculations, the magnetic moment and the exchange coupling interactions values are 1.37 μ{sub B} and J{sub 1} = 35.78meV, J{sub 2} = 40.16meV, respectively. The total magnetization, the susceptibility and the specific heat of this compound are calculated. The critical temperature obtained is in good agreement with the experimental results. Obviously, the large MCE with no hysteresis loss is obtained around T{sub C}. The maximum values of the magnetic entropy change (ΔS{sub mag}), adiabatic temperature change (ΔT{sub ad}) and the relative cooling power (RCP) are 13.41 J/kg.K, 15.96 K, 748 J/kg respectively, under applied an external magnetic field of h = 5.0 T.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗