Czochralski method for crystal growth of reactive intermetallics

Czochralski method of crystallization allows obtaining single crystals of many intermetallic compounds. New series Gd7NixPd3x (x = 2, 3) intermetallics was grown by the modi ed Czochralski method using a levitated melt in protective argon atmosphere. Preliminary studies of magnetic properties have shown that all crystals of the series order ferromagnetically. It was found that Gd7Ni2Pd shows magnetic transition to the ferromagnetic state at 225 K while Gd7Ni3 orders at 145 K

Tuning the magnetocaloric response of Gd7-xYxPd3 (2 ≤ x ≤ 6) alloys by microstructural modifications

We investigated the influence of microstructural changes on the magnetic properties and the magnetocaloric response of the Gd7-xYxPd3 (2 ≤ x ≤ 6) alloys rapidly quenched by vacuum suction casting (rc-cast samples) and melt-spinning (melt-spun samples) techniques. Quenched-in structural disorder determines magnetic and magnetocaloric properties in both series of alloys. For the rc-cast samples two distinct magnetic transitions are visible. The peak at higher temperatures is related to the ferromagnetic/paramagnetic transition of the crystalline phase. In contrast, the peak observed at low temperatures is believed to be related to the ferro-para transition of the amorphous phase and/or a spin reorientation. The Gd7-xYxPd3 alloys in the form of rapidly cooled cast exhibit the magnetic transition temperatures at 262 K, 242 K, 202 K, 153 K and 9 K, for 2 ≤ x ≤ 6 respectively. Curie temperatures of the melt-spun Gd7-xYxPd3 alloys are much lower compared to the rc-cast samples. The melt-spun Gd5Y2Pd3 orders ferromagnetically below 90 K, while Gd4Y3Pd3, Gd3Y4Pd3, Gd2Y5Pd3 and GdY6Pd3 ribbons undergo the magnetic transformation at 65 K, 40 K, 25 K, and 9 K, respectively. Investigated ribbons exhibit almost doubled magnetic entropy change in comparison to the rc-cast samples. For instance, the -ΔSm value for melt-spun and rc-cast Gd5Y2Pd3 is equal to 6.31 Jkg-1K-1 and 3.64 Jkg-1K-1, respectively. Moreover, due to the large δTFWHM of the magnetic entropy change peak, both the melt-spun and rc-cast samples exhibit large relative cooling power (RCP), reaching 466 Jkg-1 (Δμ0H = 5 T) for the rc-cast Gd5Y2Pd3. RCP values are comparable to those of some potential magnetic refrigerants

Effect of Magnesium Substitution on Dielectric Constant of Zn2-xMgxInV3O11 (x = 0.0, 0.4, 1.6) Solid Solutions

The results of magnetic and dielectric measurements of Zn2xMgxInV3O11 phases with x = 0:0, 0.4, and 1.6 showed diamagnetic behavior above room temperature and a strong increase in the relative electrical permittivity, "r, with an increase in the magnesium content as well as the high loss tangent, tan , above 150 K, irrespective of the magnesium content in the sample. With the increase in the frequency of the electric field both "r and tan strongly decreased. At low temperatures a residual paramagnetism coming from the paramagnetic ions of vanadium was observed. These effects were interpreted within a framework of the vacancy trapping centers acting as the accumulation of electric charges on the one hand and a mixed valence of vanadium ions on the other

Combustion synthesis, structural, magnetic and dielectric properties of Gd3+-doped lead molybdato–tungstates

Gd3+-doped lead molybdato–tungstates with the chemical formula of Pb1–3x□xGd2x(MoO4)1–3x(WO4)3x (where x = 0.0455, 0.0839, 0.1430, corresponding to 9.53, 18.32, 33.37 mol% of Gd3+, respectively, as well as □ denotes cationic vacancies) were successfully synthesized via combustion route. The XRD and SEM results confirmed the formation of single-phase, tetragonal scheelite-type materials (space group I41/a) with the uniform, spherical and oval grains ranging from 5 to 20 μm. Individual grains are strongly agglomerated into big clusters with the size even above 50 μm. The magnetic measurements as well as the Brillouin fitting procedure showed paramagnetic state with characteristic superparamagnetic-like behaviour and the short-range ferromagnetic interactions. The electrical and broadband dielectric spectroscopy studies revealed insulating properties with the residual electrical n-type conduction of 2×10–9 S/m and low energy loss (tanς ~ 0.01) below 300 K. Dielectric analysis showed that no dipole relaxation processes in the Gd3+-doped materials were observed. A fit of dielectric loss spectra of Gd3+-doped samples by sum of the conductivity and the Havriliak–Negami, Cole–Cole, and Cole–Davidson functions confirmed this effect

Dielectric and magnetic characteristics of Ca1−xMnxMoO4 (0 ≤ x ≤ 0.15) nanomaterials

Scheelite-type Ca1−xMnxMoO4 (x = 0.0,0.01, 0.05, 0.10 and 0.15) nanomaterials were successfully synthesized via a combustion route. Dielectric studies showed a weak n-type electrical conductivity characteristic for insulators and low relative permittivity (εr < 15) decreasing with increasing Mn2+ content. CaMoO4 and Mn2+-doped nanomaterials are chemically compatible with Al and Ag electrodes and promising for lowtemperature co-fired ceramic applications. Magnetic studies showed, at room-temperature diamagnetism for pure CaMoO4, the balance between diamagnetism and paramagnetism for Ca1−xMnxMoO4 (x = 0.01) and paramagnetic behaviour when 0.05 ≤ x ≤ 0.15 as well as the short-range antiferromagnetic interactions growing in strength as Mn2+ content increases. The Landé factor fitting procedure showed a spin-only contribution to the magnetic moment. CaMoO4 matrix unexpectedly revealed the residual paramagnetism at low temperatures derived probably from the molybdenum ions having unpaired 4d electrons as well as a paramagneticdiamagnetic transition at 70 K

Dipole relaxation process and giant dielectric permittivity in Eu3+- doped CdMoO4 single crystal

Single crystal of Eu3+-doped cadmium molybdate (Cd0.9268 M 0.0244Eu0.0488MoO4, where M denotes cationic vacancies) has been successfully grown by the Czochralski method in air and under 1 MPa. X-ray diffraction analysis indicates that as-grown single crystal exhibits tetragonal scheelite-type structure (a = b = 5.16188(14) A; c = 11.2080(5) A; space group I41/a). Eu3+ ions do not show long-range order and they are randomly distributed in CdMoO4 framework substituting Cd2+ ones. UVevis diffuse reflectance measurements revealed very close optical band gap (Eg) values, i.e. ~1.74 eV along [100] and [001] crystallographic directions that are twice smaller than Eg of microcrystalline pure CdMoO4 as well as powder Eu3+-doped single crystal. Magnetic and electrical studies of Eu3+-doped cadmium molybdate single crystal showed a paramagnetic and n-type semiconducting behaviour with the metal-insulator transition above 350 K along both crystallographic directions. Dielectric results analysis using the Cole-Cole fit function revealed that the dipole relaxation process has different time scale depending on the crystallographic direction and exhibits Arrhenius temperature dependence for both studied directions. This fact is accompanied by the colossal dielectric permittivity with er > 8 • 103. The above results are considered in the framework of narrow europium multiplets of energy comparable to thermal energy

Effect of Gd3+ substitution on thermoelectric power factor of paramagnetic Co2+-doped calcium molybdato-tungstates

A series of Co2+-doped and Gd3+-co-doped calcium molybdato-tungstates, i.e., Ca13xyCoy xGd2x(MoO4)13x(WO4)3x (CCGMWO), where 0 < x 0.2, y = 0.02 and represents vacancy, were successfully synthesized by high-temperature solid-state reaction method. XRD studies and diffuse reflectance UV–vis spectral analysis confirmed the formation of single, tetragonal scheelite-type phases with space group I41/a and a direct optical band gap above 3.5 eV. Magnetic and electrical measurements showed insulating behavior with n-type residual electrical conductivity, an almost perfect paramagnetic state with weak short-range ferromagnetic interactions, as well as an increase of spin contribution to the magnetic moment and an increase in the power factor with increasing gadolinium ions in the sample. Broadband dielectric spectroscopy measurements and dielectric analysis in the frequency representation showed a relatively high value of dielectric permittivity at low frequencies, characteristic of a space charge polarization and small values of both permittivity and loss tangent at higher frequencies

Influence of crystallite size on the magnetic order in semiconducting ZnCr2Se4 nanoparticles

Structural, electrical, magnetic, and specific heat measurements were carried out on ZnCr2Se4 single crystal and on nanocrystals obtained from the milling of this single crystal after 1, 3, and 5 h, whose crystallite sizes were 25.2, 2.5, and 2 nm, respectively. For this purpose, the high-energy ball-milling method was used. The above studies showed that all samples have a spinel structure, and are p-type semiconductors with less milling time and n-type with a higher one. In turn, the decrease in crystallite size caused a change in the magnetic order, from antiferromagnetic for bulk material and nanocrystals after 1 and 3 h of milling to spin-glass with the freezing temperature Tf = 20 K for the sample after 5 h of milling. The spin-glass behavior for this sample was derived from a broad peak of dc magnetic susceptibility, a splitting of the zero-field-cooling and field-cooling susceptibilities, and from the shift of Tf towards the higher frequency of the ac susceptibility curves. A spectacular result for this sample is also the lack of a peak on the specific heat curve, suggesting a disappearance of the structural transition that is observed for the bulk single crystal

Magnetic and Electrical Characteristics of Nd³⁺-Doped Lead Molybdato-Tungstate Single Crystals

Single crystals of Pb1−3x▯xNd2x(MoO4)1−3x(WO4)3x (PNMWO) with scheelite-type structure, where ▯ denotes cationic vacancies, have been successfully grown by the Czochralski method in air and under 1 MPa. This paper presents the results of structural, optical, magnetic and electrical, as well as the broadband dielectric spectroscopy measurements of PNMWO single crystals. Research has shown that replacing diamagnetic Pb2+ ions with paramagnetic Nd3+ ones, with a content not exceeding 0.01 and possessing a screened 4f-shell, revealed a significant effect of orbital diamagnetism and Van Vleck’s paramagnetism, n-type electrical conductivity with an activation energy of 0.7 eV in the intrinsic area, a strong increase of the power factor above room temperature for a crystal with x = 0.005, constant dielectric value (~30) and loss tangent (~0.01) up to room temperature. The Fermi energy (~0.04 eV) and the Fermi temperature (~500 K) determined from the diffusion component of thermopower showed shallow donor levels