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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Synthesis and Characterization of Er-Doped Nano ZnO Samples

Pure and erbium-doped ZnO nanoparticles (Zn{sub 1−x}Er{sub x}O), (0.00 ≤ x ≤ 0.10), were synthesized by wet chemical co-precipitation method. The structural, optical, and magnetic properties of the prepared samples were investigated using x-ray powder diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV), Fourier transform infrared spectroscopy (FTIR), M-H magnetic hysteresis, and electron paramagnetic resonance (EPR). XRD studies exhibit the presence of a single ZnO wurtzite hexagonal crystal structure for 0.00 ≤ x ≤ 0.06. A secondary phase of Er{sub 2}O{sub 3} appears for x > 0.06. This means that the solubility limit for doping Zn{sup 2+} ions by Er{sup 3+} ions is about x = 0.06 under our preparations condition. The lattice parameter a is not affected by the Erbium doping. On the other hand, the lattice parameter c and the unit cell volume V increase with the increase of x up to x = 0.06. This is attributed to the larger ionic size of Er{sup 3+} ions (0.88 Å) compared to Zn{sup 2+} ions (0.74 Å). Both c and V decrease for x > 0.06. TEM micrographs indicate that the shape and the size of the ZnO nanoparticles are modified by changing the doping level of Er. The UV measurements point out that band gap energy E{sub g} decreases with the increase of x up to x = 0.06. Then, it increases for both x = 0.08 and 0.10. FTIR spectra confirm the presence of O–H and Zn–O stretching modes at 3451.963 and 428.901 cm{sup − 1}, respectively, in pure and doped ZnO samples. The Zn–O stretching mode shifts toward a lower wavenumber for x = 0.06 and toward a higher wavenumber for x = 0.10. M-H hysteresis analysis, at room temperature, reveals that the pure ZnO has a ferromagnetic signal combined with diamagnetic and paramagnetic contributions. This ferromagnetism is reduced for the doped samples up to x = 0.02, and an antiferromagnetic alignment appears for 0.04 ≤ x ≤ 0.10. The saturation magnetization (M{sub s}), the coercivity (H{sub c}), the retentivity (M{sub r}), the anisotropy constant (K{sub a}), and the magnetic moment (μ{sub m}) were estimated and discussed in terms of erbium doping for the different samples. EPR spectra for Zn{sub 1−x}Er{sub x}O were measured at room temperature in order to study the effect of Er substitution on the g value, resonance field (H{sub r}), peak to peak line width (ΔH{sub pp}) and spin–spin relaxation time constant (T{sub 2}).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural, Magnetic, and XPS Studies of the Double-Perovskite Mn{sub 2}VSbO{sub 6}

The double-perovskite Mn{sub 2}VSbO{sub 6} has been synthesized by solid-state reaction under pressure at 6 GPa and temperature of 1200°C, and its crystal structure has been refined by X-ray powder diffraction date. Mn{sub 2}VSbO{sub 6} crystallizes in monoclinic space group P12{sub 1}/n1 with the following parameters: a = 5.2340 Å (2), b = 5.3932 Å (2), c = 7.6460 Å (3), β = 89.6075° (23), V = 215.826 Å{sup 3} (14), Z = 2. It found that V and Sb atoms are completely ordered in 2d and 2c positions of double-perovskite structure, respectively. According to XPS measurements, manganese in this compound is present as Mn{sup 2+}, while vanadium is V{sup 3+}. The magnetization date suggests that Mn{sub 2}VSbO{sub 6} transforms to an antiferromagnetic state due to simultaneous ordering of V{sup 3+} and Mn{sup 2+} magnetic sublattices at low temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Annealing Temperature on Magnetic and Mössbauer Properties of ZnFe{sub 2}O{sub 4} Nanoparticles by Sol-gel Approach

In this study, spinel ZnFe{sub 2}O{sub 4} nanoparticles (NPs) were synthesized by citrate sol-gel route using nickel nitrates, ferric nitrates and citric acid by annealing at 900, 1000, and 1100{sup ∘}C. We reported the structural and magnetic properties (including Mössbauer analysis) for anisotropy ZnFe{sub 2}O{sub 4} NPs annealed at different temperatures. Fourier transform infrared (FT-IR) and X-ray powder diffraction (XRD) were utilized to analyze the structural properties of magnetic nanoparticles (MNPs). Morphological features of resultant MNPs were examined by scanning electron microscopy (SEM). The observed XRD results displayed that the crystallite size increased from 38.60 to 49.28 nm with increasing the annealing temperature in a distinct linear trend. The enhancement of saturation magnetization of the uniaxial ZnFe{sub 2}O{sub 4} NPs was studied and varied from 1.28 to 1.66 emu/g as the annealing temperature increases. The Mössbauer spectra results show that ZnFe{sub 2}O{sub 4} ferrites were paramagnetic in nature at room temperature (RT).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic Transition and Magnetocaloric Effect of Gd{sub 1−x}Nd{sub x}Mn{sub 2}Ge{sub 2} (x = 0.3 and 0.4) Compounds

Gd{sub 1−x}Nd{sub x}Mn{sub 2}Ge{sub 2} compounds with x = 0.3 and 0.4 were prepared by arc melting and crystallized in the ThCr{sub 2}Si{sub 2}-type structure with the space group I4/mmm based on X-ray powder diffraction (XRD) results. Magnetic transition and magnetocaloric effect (MCE) of the Gd{sub 1−x}Nd{sub x}Mn{sub 2}Ge{sub 2} compounds were investigated by magnetic measurements on a physical property measurement system (PPMS). Gd{sub 0.7}Nd{sub 0.3}Mn{sub 2}Ge{sub 2} compound exhibits complicated magnetic transitions at around 63 K (T{sub comp}), 86 K (T{sub 1}), 136 K (T{sub C}), 260 K (T{sub N}{sup inter}), and 347 K (T{sub C}{sup inter}), respectively, while Gd{sub 0.6}Nd{sub 0.4}Mn{sub 2}Ge{sub 2} compound shows a spin re-orientation transition at about 52 K. Combined with isothermal magnetization curves and the Maxwell relation, the maximum magnetic entropy changes of Gd{sub 0.7}Nd{sub 0.3}Mn{sub 2}Ge{sub 2} and Gd{sub 0.6}Nd{sub 0.4}Mn{sub 2}Ge{sub 2} were calculated to be 4.31 and 5.15 J kg{sup − 1} K{sup − 1} under the applied magnetic field changing from 0 to 5 T, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Structural and Magnetic Properties of La-Substituted M-Type Hexagonal Sr–Ni Ferrites Synthesized by Ball-Milling-Assisted Ceramic Process

Sr{sub 0.5}Ni{sub 0.5}La{sub x}Fe{sub 12 − x}O{sub 19} (x = 0, 0.08, 0.16, and 0.24) hexaferrites have been synthesized by ball-milling-assisted ceramic process. The calcined samples are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), and vibrating sample magnetometry (VSM). XRD reveals that all samples consist of the main M-type hexagonal Sr ferrite phase and a low amount of rhombohedral Fe{sub 2}O{sub 3} as secondary phase, and a continuous increase of the hexagonal lattice parameters with substitution content (x). Magnetic characterization indicates that all Sr{sub 0.5}Ni{sub 0.5}La{sub x}Fe{sub 12 − x}O{sub 19} samples have a hard magnetic property. Substitution of Fe{sup 3+} ions by La{sup 3+} ions can obviously improve the specific saturation magnetization, remanence, magnetic moment, and effective anisotropy constant. Specific saturation magnetization, remanence, and the magnetic moment reach a maximum at x= 0.24 and calcination temperature of 1050 {sup ∘}C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Comparative Study of the Effect of Magnetic Nanoparticle CoFe{sub 2}O{sub 4} on Fluctuation-Induced Conductivity of Y-123 and Y-358 Superconductors

In this study, a comparative investigation of the electrical conductivity fluctuations in nano-CoFe{sub 2}O{sub 4} added to Y{sub 3}Ba{sub 5}Cu{sub 8}O{sub 18±x} (Y-358) and YBa{sub 2}Cu{sub 3}O{sub 7−d} (Y-123) products is performed. All products were made using the solid-state reaction process. X-ray powder diffraction (XRD) analyses confirmed the formation of different phases. Scanning electron microscope (SEM) analysis shows the reduction of grain size with increasing the quantity of nano-CoFe{sub 2}O{sub 4} particles for both the Y-123 and Y-358 samples. The decrease of grain size is more accentuated in the case of the Y-358 samples compared with the Y-123 ones. The data of conductivity fluctuations are examined in terms of the derivative of the electrical resistivity with respect to temperature and the logarithmic derivative of the conductivity with regard to temperature. The results illustrate the existence of a transition with two stages; intragrain and intergrain. It is demonstrated that the addition of CoFe{sub 2}O{sub 4} nanoparticles affects the electrical conductivity fluctuations, the values of the critical exponents, and the fluctuation dimensionality in YBCO systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The Structural, Electronic, and Magnetic Features of Co{sub 2}Mn{sub 1−x}Al{sub x}Ti (0 ≤ x ≤ 0.6) Heusler Alloys

The structural, electronic, and magnetic features of Co{sub 2}Mn{sub 1−x}Al{sub x}Ti (0 ≤ x ≤ 0.6) Heusler alloys (HAs) have been systematically investigated by experimental techniques (X-ray powder diffraction, scanning electron microscopy, and magnetization measurements) and ab initio theoretical calculations. Whole alloys have cubic structures at room temperature and exhibit ferromagnetic properties. The Curie temperature of Co{sub 2}Mn{sub 1−x}Al{sub x}Ti (x = 0) is approximately 790 K, which is compatible with other studies. By increasing Al content, the temperature dependence of magnetization trials has proved a linear diminishment on Curie temperature and saturation magnetization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Influence of Non-magnetic Ti{sup 4+} Ion Doping at Mn Site on Structural, Magnetic, and Magnetocaloric Properties of La{sub 0.5}Pr{sub 0.2}Sr{sub 0.3}Mn{sub 1−x}Ti{sub x}O{sub 3} Manganites (x = 0.0 and 0.1)

Polycrystalline perovskite AMn{sub 1−x}TiO{sub 3} with A = La{sub 0.5}Pr{sub 0.2}Sr{sub 0.3} (x = 0.0 and 0.1) have been prepared using solid-state reaction method. X-ray powder diffraction and Rietveld refinement revealed that all samples crystallize in a rhombohedral structure with space group R 3-bar c From M–T curve, we determined the Curie temperature, where the magnetization value decreases abruptly. The Curie temperature (T{sub C}) decreases from 280 to 123 K when the percentage of Ti increases to 10%. The values of the magnetization M(H) decrease when increasing the Ti content. Moreover, the magnetocaloric effect (MCE) was estimated in terms of isothermal entropy change (−ΔS{sub M}) using the M(T, μ{sub 0}H) data and employing the thermodynamic Maxwell equation. In addition, using a phenomenological model, we determine magnetocaloric effect from the calculation of magnetization as a function of temperature under different external magnetic fields. Also, we can determine the relative cooling power (RCP) and the specific heat which varies from 2.803 to 7.354 J/(kg/K) for the undoped sample from M(T, μ{sub 0}H) data at different magnetic fields theoretically.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Effects of La Doping on the Crystal Structure, Magnetic, and Microwave Absorption Properties of Nd{sub 2}Fe{sub 14}B Compound

The crystal structure, magnetic, and microwave absorption properties of the (Nd{sub 1−x}La{sub x}){sub 2}Fe{sub 14}B system have been investigated. The La{sub 2}Fe{sub 14}B compound was successfully synthesized and refined, giving a tetragonal structure, space group P4{sub 2}/mnm with the Nd{sub 2}Fe{sub 14}B-type structure. The crystal structure parameters of the (Nd{sub 1−x}La{sub x}){sub 2}Fe{sub 14}B compounds were determined by full-profile Rietveld refinements. The results revealed that all intermediate alloys form a continuous solid solution. The normalized lattice parameters of the (Nd{sub 1−x}La{sub x}){sub 2}Fe{sub 14}B compounds increase linearly with an increase of La concentration. Based on the results of DSC measurements and X-ray powder diffraction examinations, the phase diagram of the Nd{sub 2}Fe{sub 14}B-La{sub 2}Fe{sub 14}B system has been constructed. The remanence (M{sub r}) and coercivity (H{sub c}) of (Nd{sub 1−x}La{sub x}){sub 2}Fe{sub 14}B (x = 0.00, 0.10, 0.20, 0.30, and 0.40) gradually decrease. The highest reflection loss is − 29.8, − 27.4, − 24.1, − 18.6, and − 14.2 dB at 9.8, 8.9, 7.5, 6.9, and 6.5 GHz, respectively. The absorption peak shifts toward from higher frequency region to lower frequency region and the absorption bandwidth widens with the increase of the La substitution.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Ca Doping on the Structure and Magnetic and Electronic Properties of La{sub 1 − x}Ca{sub x}Cr{sub 0.8}Cu{sub 0.2}O{sub 3} (x = 0~0.3)

A series of La{sub 1 − x}Ca{sub x}Cr{sub 0.8}Cu{sub 0.2}O{sub 3} samples were successfully prepared by sol-gel method, and their crystal structures were refined by using X-ray powder diffraction data. All samples had orthorhombic structure with a space group Pbnm. Two magnetic transitions were observed for all of samples, and the paramagnetism-antiferromagnetism transition temperature decreased, and the antiferromagnetism-ferromagnetism transition temperature increased with increasing Ca content. Moreover, Cu and Ca co-doping improved conductivity and active energy.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Vickers Microhardness Studies for SmBa{sub 2}Cu{sub 3}O{sub 7-δ} Added with NiO Nanosized Particles

The effect of nanosized particles NiO addition on the Vickers microhardness of polycrystalline SmBa{sub 2}Cu{sub 3}O{sub 7-δ} was investigated. Various amounts of nanosized particles NiO (x = 0.00, 0.02, 0.04, 0.08, and 0.12 wt%) were added to SmBa{sub 2}Cu{sub 3}O{sub 7-δ} prepared by the solid-state reaction method. Sample characterizations were carried out using X-ray powder diffraction (XRD), particle induced X-ray emission (PIXE), Rutherford backscattering (RBS), and scanning electron microscopy (SEM). The nanosized particle addition does not influence the orthorhombic structure of SmBa{sub 2}Cu{sub 3}O{sub 7-δ}, whereas it affects the oxygen content δ. The electrical and mechanical properties of (NiO){sub x}SmBa{sub 2}Cu{sub 3}O{sub 7-δ} samples were measured using four-standard probe technique and Vickers microhardness in order to investigate the effect of NiO nanosized particles on superconducting transition temperature and Vickers microhardness number H{sub v}. The Vickers microhardness data were analyzed using Hays and Kendall (HK), elastic plastic deformation (EPD), and modified proportional specimen resistance (MPSR) models. The analysis showed that the MPSR model was found to be the best to describe the behavior of H{sub v}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Mössbauer, Magnetization and Structure Characterizations of the Annealed Sr{sub 1/3}Mn{sub 1/3}Co{sub 1/3}Fe{sub 2}O{sub 4} Ferrite Nanoparticles

Sr{sub 1/3}Mn{sub 1/3}Co{sub 1/3}Fe{sub 2}O{sub 4} ferrite nanoparticles were synthesized by glycol thermal technique. The structure and morphology of the Nano ferrites were studied by X-ray powder diffraction, Fourier transform infrared FTIR, high-resolution scanning electron microscopy, and high-resolution transmission electron microscopy. The induced internal strains were investigated by Williamson plots. The results show mono-dispersive property of the sample and particle sizes that increase with increasing annealing temperature, T{sub A}. The magnetic hyperfine fields were found to be sensitive to T{sub A} as seen from room temperature {sup 57}Fe Mössbauer measurements. The magnetic hysteresis loops were performed in external magnetic field of up to 50 kOe. Room temperature M − H loops showed that the coercive fields increased to a maximum at T{sub A} of 500 °C and then decreased thereafter. Significant increases in coercive fields were observed at a measuring temperature of 4 K. Distortions in the hysteresis loops at 4 K were observed where thermal annealing effect appears to induce strong linear correlation between coercive fields and saturation magnetizations.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Synthesis and Characterization of Hydrophobic Fe{sub 3}O{sub 4} Magnetic Nanoparticles with High Saturation Magnetization

A simple one-step solvothermal method is proposed to prepare hydrophobic Fe{sub 3}O{sub 4} nanoparticles (MNPs) using iron acetylacetonate (Fe(acac){sub 3}), oleylamine (OAm), and ethylene glycol (EG). X-ray powder diffraction, scanning electron microscope, infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectrometry, and vibrating sample magnetometer are used to characterize the structure, morphology, and properties of products. The testing results indicate that the as-synthesized products are spherical-like hydrophobic MNPs, superparamagnetic at room temperature, with a saturation magnetization up to 76.8 emu/g. The good hydrophobic property of MNPs is attributed to the coverage of oleylamine, without causing a remarkable loss of magnetic property. In addition, the influences of material ratio, aging time, oleic acid, and stearic acid used as additives are studied in our research.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Morphology, UV–visible and ellipsometric studies of sodium lithium orthovanadate

Sodium lithium orthovanadates were prepared by the classic ceramic method technique. Structure, phase purity, composition, and morphology were characterized by X-ray powder diffraction, infrared spectroscopy, energy dispersive spectroscopy, scanning-electron microscopy and atomic force microscopy. The optical properties of Na{sub x}Li{sub 1−x}CdVO{sub 4} (x = 0.5, 1) compounds prepared were recorded at room temperature using ultra-visible and ellipsometric spectroscopies in the spectral range (200–800) nm. The average reflectance of the pellets showed high reflectivity (over 80%) in the visible spectrum. The UV–Vis absorption bands are assigned to the charge transfer from the oxygen ligands to the central vanadium atom inside the [VO{sub 4}]{sup 3−} groups in the orthovanadate compounds. The optical band gaps E{sub g} of both samples are evaluated using Kubelka–Munk function. The analysis of the data revealed the existence of optical allowed direct transition for Na{sub x}Li{sub 1−x}CdVO{sub 4} (x = 0.5, 1). Spectroscopic ellipsometry measurements have been performed on Na{sub x}Li{sub 1−x}CdVO{sub 4} (x = 0.5, 1) specimens and their optical properties were analyzed using the Cauchy model.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Divanadium substituted keggin [PV 2 W 10 O 40 ] on non-reducible supports-Al 2 O 3 and SiO 2 : synthesis, characterization, and catalytic properties for oxidative dehydrogenation of propane

Molecular metal oxide cluster, K 5 [α-1,2-PV 2 W 10 O 40 ] (PV 2 W 10 ), was found to have intrinsic catalytic activity for the oxidative dehydrogenation of propane with high selectivity (> 80%) to propylene at low propane conversion (0.3%). Synthesis of dispersed PV 2 W 10 in non-reducible supports, γ-Al 2 O 3 and SiO 2 , was done by incipient wetness impregnation. The supported catalysts were characterized by IR, Raman spectroscopy, nitrogen adsorption, x-ray powder diffraction (PXRD), elemental analysis, hydrogen temperature-programmed reduction (H 2 –TPR), and ammonia temperature-programmed desorption (NH 3 –TPD). Catalytic testing of the supported PV 2 W 10 at equimolar cluster concentration revealed that when supported in γ-Al 2 O 3 it is more active (sevenfold increase in propane conversion) but in SiO 2 it is more selective to propylene (94%). The observed performance was due to both an increase in reducibility and higher concentration of strong acid sites for PV 2 W 10 supported in γ-Al 2 O 3 versus SiO 2 . Lastly, PV 2 W10 was shown to remain intact under reaction conditions indicating its thermal and oxidative stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Synthesis and Structural Characterization of Sb-Doped TiFe{sub 2}Sn Heusler Compounds

Ternary Heusler compounds form a numerous class of intermetallics, which include two families with general compositions ABC and AB{sub 2}C, usually referred to as half- and full-Heusler compounds, respectively. Given their tunable electronic properties, made possible by adjusting the chemical composition, these materials are currently considered for the possible use in sustainable technologies such as solar energy and thermoelectric conversion. According to theoretical predictions, Sb substitution in the TiFe{sub 2}Sn full-Heusler compound is thought to yield band structure modifications that should enhance the thermoelectric power factor. In this work, we tested the phase stability and the structural and microstructural properties of such heavily doped compounds. We synthesized polycrystalline TiFe{sub 2}Sn{sub 1−x}Sb{sub x} samples, with x = 0, 0.1, 0.2 and 1.0 by arc melting, followed by an annealing treatment. The structural characterization, performed by x-ray powder diffraction and microscopy analyses, confirmed the formation of the pseudo-ternary Heusler structure (cF16, Fm-3m, prototype: MnCu{sub 2}Al) in all samples, with only few percent amounts of secondary phases and only slight deviations from nominal stoichiometry. With increasing Sb substitution, we found a steady decrease in the lattice parameter, confirming that the replacement takes place at the Sn site. Quite unusually, the as-cast samples exhibited a higher lattice contraction than the annealed ones. The fully substituted x = 1.0 compound, again adopting the MnCu{sub 2}Al structure, does not form as stoichiometric phase and turned out to be strongly Fe deficient. The physical behavior at room temperature indicated that annealing with increasing temperature is beneficial for electrical and thermoelectrical transport. Moreover, we measured a slight improvement in electrical and thermoelectrical properties in the x = 0.1 sample and a suppression in the x = 0.2 sample, as compared to the undoped x = 0 sample.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Chemical Composition on the Microstructure and Properties of the Ag-Ga-Ge Alloys

This study presents a comparison of thermodynamically calculated phase compositions of Ag-Ga-Ge alloys at fixed temperatures with phase analysis results of alloys annealed at respective temperatures. Three isothermal sections of the Ag-Ga-Ge system at 25, 100 and 300 °C have been extrapolated using optimized thermodynamic parameters from the literature. An experimental analysis of the microstructure was carried out using optical microscopy, scanning electron microscopy and energy-dispersive spectrometry. Results obtained by x-ray powder diffraction methods (identified phases and lattice parameters) were compared with the results of the predicted phase equilibria. Good overall agreement between experimental and calculated values was obtained. The Brinell hardness and electrical conductivity of selected alloys were measured and obtained results were analyzed with respect to their overall compositions and phase constituents.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Magnetostructural phase transitions and magnetocaloric effect in (Gd 5-x Sc x )Si 1.8 Ge 2.2

Future advancements in magnetocaloric refrigeration/heat pumping technologies depend on the discovery of new materials that demonstrate large, tunable magnetocaloric effects (MCEs) in the vicinity of coupled magnetic and structural phase transitions that occur reversibly with minimum hysteresis. Here, with this in mind, we investigate phase transitions, microstructure, magnetic, thermal, magnetocaloric, and transport properties of (Gd 5-x Sc x )Si 1.8 Ge 2.2 compounds. Replacement of magnetic Gd with non-magnetic Sc in Gd 5-x Sc x Si 1.8 Ge 2.2 increases the ferromagnetic to paramagnetic first order phase transition temperature, T C , with only a minor reduction in MCE when x ≤ 0.2. We also demonstrate that hydrostatic pressure further increases T C and reduces the hysteresis of the first order phase transition in Gd 4.8 Sc 0.2 Si 1.8 Ge 2.2 from 7 to 4 K. Temperature-dependent x-ray powder diffraction study of Gd 4.8 Sc 0.2 Si 1.8 Ge 2.2 confirms the monoclinic ↔ orthorhombic structural transformation at T C , in agreement with magnetic, calorimetric, and electrical transport measurements. In addition to the substantial magnetocaloric effect, a large magnetoresistance of ~20% is also observed in Gd 4.8 Sc 0.2 Si 1.8 Ge 2.2 for ΔH = 50 kOe in the vicinity of the magnetostructural transition. Finally, in a drastic reversal of the initial doping behavior further additions of Sc (x > 0.2) suppress formation of the monoclinic phase, change the nature of the transition from first-to second-order, and reduce both the transition temperature and magnetocaloric effect.

36 MATERIALS SCIENCE↗