The magnetocaloric effect (MCE) of polycrystalline gadolinium was studied in high steady magnetic fields up to 14 T by direct measurements of the adiabatic temperature change (ΔT) using an ..."extraction method". Large MCE was observed at the ferromagnetic phase transition resulting in ΔT of 19.5 K at a field change of 14 T. The direct measurements of MCE were performed using the measuring system designed and constructed by the authors. It was shown that near the Curie temperature, the magnetic field dependence of the adiabatic temperature change is far from saturation even in a 14 T field and is adequately described by the thermodynamic Landau theory for magnetic second-order phase transitions.
•The equiatomic MnZnSb compound were prepared.•Its magnetic properties and magnetocaloric effect (MCE) were systematically studied.•A considerable reversible MCE was observed for MnZnSb around its ...own Curie temperature.•The origin of MCE and its potential application in MnZnSb were discussed.•The field dependence of the MCE was described in frames of the thermo-dynamic theory.
The equiatomic intermetallic alloy MnZnSb with a tetragonal Cu2Sb-type crystal structure (space group P4/nmm) was melted in the resistance furnace in the evacuated quartz ampoule. The adiabatic temperature change (ΔTad) and the isothermal variation of the magnetic entropy (ΔSM) of the MnZnSb compound near to the magnetic phase transition were studied. The ΔTad in a magnetic field up to 1.25 T was studied by the direct method. It was found that temperature dependencies of both ΔTad and ΔSM show a sharp peak near room temperature with a maximum at Curie temperature TC = 317 K. It was shown that there is no temperature hysteresis of the ΔTad in MnZnSb, and the maximum of ΔTad when the compound is heated or cooled is detected at the same temperature. The estimated value of ΔTad in a field of 14 T is 4.5 K. It was shown that near the Curie temperature, the field dependence of the maximum of magnetic entropy change is adequately described by the thermodynamic Landau theory for magnetic second-order phase transitions.
This paper presents the study of the magnetic properties and magnetocaloric effect (MCE) of the rare-earth ferrimagnetic Dy2Fe10Al7 compound. The field and temperature dependencies of the ...magnetization in the temperature range 4.2–300 K were studied in magnetic fields up to 100 kOe. The MCE was studied by direct method in magnetic fields up to 70 kOe. It was established that the sign of the MCE changes from positive to negative near the compensation temperature. It was shown from the obtained experimental results and the theoretical estimations that the temperature and field dependencies of the MCE in rare-earth ferrimagnet differ from those in ferromagnetic materials. The effective field (Heff2) determined from the values of the MCE near to the compensation temperature are in a good agreement with those reported earlier.
Display omitted
•The magnetization, susceptibility, and MCE in Dy2Fe10Al7 were investigated.•The MCE was studied by direct methods.•It is shown that the exchange field value can be estimated from the MCE data.•The influence of ferrimagnetic structure on magnetocaloric effect in Dy2Fe10Al7 compound.
•The magnetostrictions of Tb0.2Gd08 single crystal were measured up to 14 T.•The giant linear and volume magnetostriction was found in Tb0.2Gd0.8 single crystal.•The magnetostriction constants of ...Tb0.2Gd08 single crystal were determined.•At low temperatures the magnetostriction is caused MCA and exchange interactions.•Two-ion exchange interaction is responsible for the giant magnetostriction at TC.
Temperature and field dependencies of the magnetostriction of the Tb0.2Gd0.8 single crystal were measured in strong magnetic fields up to 14 T in a temperature range of 4.2–300 K. The temperature dependencies of five magnetostriction constants λ1α,0, λ2α,0, λ1α,2, λ2α,2 and λγ,2 were determined, using Clark's theory for rare-earth hexagonal close-packed single crystals. Giant values of linear and volume magnetostriction due to forced magnetostriction were found in the Tb0.2Gd0.8 single crystal (λbc = 1.6 × 10−3) in the region of the Curie temperature (near room temperatures). It is shown that giant values of forced magnetostriction are caused by the sharp dependence of exchange interactions on interatomic distances along the hexagonal the c axis.
We simulate numerically steady-state RayleighaBACOnard convection slightly above the stability threshold in a stratified supercritical fluid. We use a two-dimensional approximation and consider one ...roll contained in a square cell. Simulations are performed by two different numerical codes. First code is based on the complete Navier-Stokes equations, and second one is a low Mach number approximation with filtering sound and stratification effects. We consider conditions in which an influence of adiabatic temperature gradient is significant. Solutions found on the basis of two mathematical models are matched in a special fashion to find a contribution of adiabatic temperature gradient and specify common features independent of whether the governing equations are able to predict a stratification effect. We perform a comparison with known analytical and experimental results and propose our solutions as benchmark data for supercritical RayleighaBACOnard convection.
Magnetic properties of hydrides of the intermetallic compound NdeFe14BHx are investigated in the temperature range covering the Curie temperatures (TC) of the compounds (up to 670 K). The temperature ...dependencies of magnetization are measured under continuous control of hydrogen content in the investigated samples. The dependencies of Curie and spin-reorientation transition (TSR) temperatures on the hydrogen concentration are studied in detail. The dependence of hydrogen concentration on pressure at a constant temperature (near TC) and on the temperature at various pressures are obtained. We attempted to estimate the contributions of the unit cell volume increase upon hydrogenation and the electronic structure change in the variation of TC of the hydrogenated Nd2Fe14B.
Status of laser polarimeter at VEPP-4M Blinov, V.E.; Bedareva, T.V.; Zakharov, S.A. ...
Journal of instrumentation,
08/2020, Letnik:
15, Številka:
8
Journal Article
Recenzirano
Laser polarimeter facility at VEPP-4M accelerator is designed to calibrate the beam energy by resonance depolarization method in the energy region of the Υ-meson. The laser trigger and laser ...polarization control system has been upgraded. A new water-cooled vacuum mirror is being developed.
The hydride NdMnGeH with the tetragonal ZrSiCuAs-type of structure (P4/nmm, N129, tP8) was obtained by hydrogen absorption at 523 K and 1 MPa from the NdMnGe intermetallic compound with a the ...tetragonal CeFeSi crystal structure (P4/nmm, N129, tP6). Measurements of magnetization in high magnetic fields up to 60 T and heat capacity measurements reveal pronounced changes in the magnetic properties of NdMnGe after hydrogenation. The Nd sublattice changes its ordering type from ferromagnetic to the antiferromagnetic one with a more than twofold decrease of and its magnetic ordering temperature (from 199 to 84 K). We explain the observed effects by the altered exchange interactions within the Nd sublattice resulting from the changed Nd–Nd interplane distances by interstitial atoms. The results are compared with data obtained previously for the NdMn1-xTixGe compounds, where the Ti substitution also changes significantly the magnetic properties.
•A new hydride NdMnGeH was obtained.•The crystal structure of NdMnGeH adopts the space group of the parent NdMnGe.•After hydrogenation the Nd sublattice changes its ordering type.
A laser polarimeter at the VEPP-4M storage ring is being developed for the beam energy calibration by the resonant depolarization method in the future high-precision measurements of the Υ meson ...masses with the KEDR detector. The status of the laser polarimeter and first energy measurements at 4.1 GeV with an accuracy of 50 keV is described.
Several firn/ice cores were recovered from the Siberian Altai (Belukha plateau), central Tien Shan (Inilchek glacier) and the Tibetan Plateau (Zuoqiupu glacier, Bomi) from 1998 to 2003. The ...comparison analyses of stable-isotope/geochemistry records obtained from these firn/ice cores identified the physical links controlling the climate-related signals at the seasonal-scale variability. The core data related to physical stratigraphy, meteorology and synoptic atmospheric dynamics were the basis for calibration, validation and clustering of the relationships between the firn-/ice-core isotope/ geochemistry and snow accumulation, air temperature and precipitation origin. The mean annual accumulation (in water equivalent) was 106 gcm−2 a−1 at Inilchek glacier, 69 gcm−2 a−1 at Belukha and 196 g cm−2 a−1 at Zuoqiupu. The slopes in regression lines between the δ18O ice-core records and air temperature were found to be positive for the Tien Shan and Altai glaciers and negative for southeastern Tibet, where heavy amounts of isotopically depleted precipitation occur during summer monsoons. The technique of coupling synoptic climatology and meteorological data with δ18O and d-excess in firn-core records was developed to determine climate-related signals and to identify the origin of moisture. In Altai, two-thirds of accumulation from 1984 to 2001 was formed from oceanic precipitation, and the rest of the precipitation was recycled over Aral–Caspian sources. In the Tien Shan, 87% of snow accumulation forms by precipitation originating from the Aral–Caspian closed basin, the eastern Mediterranean and Black Seas, and 13% from the North Atlantic.
PDF
