Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userRoom temperature magnetic entropy change and magnetoresistance in La_{0.70}(Ca_{0.30-x}Sr_x)MnO_3:Ag 10% (x = 0.0-0.10)
243
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The magnetic and magnetocaloric properties of polycrystalline La0.70(Ca0.30-xSrx)MnO3:Ag 10% manganite have been investigated. All the compositions are crystallized in single phase orthorhombic Pbnm space group. Both, the Insulator-Metal transition temperature (TIM) and Curie temperature (Tc) are observed at 298 K for x = 0.10 composition. Though both TIM and Tc are nearly unchanged with Ag addition, the MR is slightly improved. The MR at 300 K is found to be as large as 31% with magnetic field change of 1Tesla, whereas it reaches up to 49% at magnetic field of 3Tesla for La0.70Ca0.20Sr0.10MnO3:Ag0.10 sample. The maximum entropy change (DeltaSMmax) is 7.6 J.Kg-1.K-1 upon the magnetic field change of 5Tesla, near its Tc (300.5 K). The La0.70Ca0.20Sr0.10MnO3:Ag0.10 sample having good MR (31%1Tesla, 49%3Tesla) and reasonable change in magnetic entropy (7.6 J.Kg-1.K-1, 5 Tesla) at 300 K can be a potential magnetic refrigerant material at ambient temperatures.
rate research
Read More
We report the observation of large magnetocaloric effect near room temperature in antipervoskite SnCMn3. The maximal magnetic entropy change at the first-order ferrimagnetic-paramagnetic transition temperature (TC 279 K) is about 80.69mJ/cm3 K and 133mJ/cm3 K under the magnetic field of 20 kOe and 48 kOe, respectively. These values are close to those of typical magnetocaloric materials. The large magnetocaloric effect is associated with the sharp change of lattice, resistivity and magnetization in the vicinity of TC. Through the measurements of Seebeck coefficient and normal Hall effect, the title system is found to undergo a reconstruction of electronic structure at TC. Considering its low-cost and innocuous raw materials, Mn-based antiperovskite compounds are suggested to be appropriate for pursuing new materials with larger magnetocaloric effect.
We measured thermal conductivity, k, thermoelectric power, S, and dc electric conductivity, sigma, of La_{5/8-x}Pr_{x}Ca_{3/8}MnO_{3}, showing an intricate interplay between metallic ferromagnetism (FM) and charge ordering (CO) instability. The change of k, S and sigma with temperature (T) and x agrees well with the effective medium theories for binary metal-insulator mixtures. This agreement clearly demonstrates that with the variation of T as well as x, the relative volumes of FM and CO phases drastically change and percolative metal-insulator transition occurs in the mixture of FM and CO domains.
La0.7Ba0.3MnO3 (LBMO):Agx (x = 0.0, 0.1, 0.2, 0.3, and 0.4) composites are synthesized by solid-state reaction route, the final sintering temperatures are varied from 1300 (LBMO1300Ag) to 1400 0C (LBMO1400Ag), and their physical properties are compared as a function of temperature and Ag content. All samples are crystallized in single phase accompanied by some distortion in main structural phase peaks at higher angles with increase in silver content. Though the lattice parameters (a, c) decrease, the b increases slightly with an increase in Ag content. The scanning electron micrographs (SEM) showed better grains morphology in terms of size and diffusion of grain boundaries with an increase in Ag content. In both LBMO1300Ag and LBMO1400Ag series the metal insulator transition (TMI) and accompanied paramagnetic-ferromagnetic transition (TC) temperatures are decreased with increase in Ag content. The sharpness of MI transition, defined by temperature coefficient of resistance (TCR), is improved for Ag added samples. At a particular content of Ag(0.3), the TMI and TC are tuned to 300K and maximum magneto-resistance at 7Tesla applied field (MR7T) of up to 55% is achieved at this temperature, which is more than double to that as observed for pure samples of the both 1300 and 1400 0C series at same temperature. The MR7T is further increased to above 60% for LBMOAg(0.4) samples, but is at 270K. The MR7T is measured at varying temperatures of 5, 100, 200, 300, and 400K in varying fields from +/- 7 Tesla, which exhibits U and V type shapes. Summarily, the addition of Ag in LBMO improves significantly the morphology of the grains and results in better physical properties of the parent manganite system.
We report synthesis, structural details and magnetization of SmFe1-xCoxAsO with x ranging from 0.0 to 0.30. It is found that Co substitutes fully at Fe site in SmFeAsO in an iso-structural lattice with slightly compressed cell. The parent compound exhibited known spin density wave (SDW) character below at around 140 K. Successive doping of Co at Fe site suppressed the SDW transition for x = 0.05 and later induced superconductivity for x = 0.10, 0.15 and 0.20 respectively at 14, 15.5 and 9K. The lower critical field as seen from magnetization measurements is below 200Oe. The appearance of bulk superconductivity is established by wide open isothermal magnetization M(H) loops. Superconductivity is not observed for higher content of Co i.e. x = 0.30. Clearly the Co substitution at Fe site in SmFe1-xCoxAsO diminishes the Fe SDW character, introduces bulk superconductivity for x between 0.10 and 0.20 and finally becomes non-superconducting for x above 0.20. The Fe2+ site Co3+ substitution injects mobile electrons to the system and superconductivity appears, however direct substitution introduces simultaneous disorder in superconducting FeAs layer and thus superconductivity disappears for higher content of Co.
Nanoparticles (dia ~ 5 - 7 nm) of Bi_0.5 X_0.5(X=Ca,Sr)MnO_3 are prepared by polymer assisted sol-gel method and characterized by various physico-chemical techniques. X-ray diffraction gives evidence for single phasic nature of the materials as well as their structures. Mono dispersed to a large extent, isolated nanoparticles are seen in the transmission electron micrographs. High resolution electron microscopy shows the crystalline nature of the nanoparticles. Superconducting quantum interferometer based magnetic measurements from 10 K to 300 K show that these nanomanganites retain the charge ordering (CO) nature unlike Pr and Nd based nanomanganites. The CO in Bi based manganites is thus found to be very robust consistent with the observation that magnetic field of the order of 130 T are necessary to melt the CO in these compounds. These results are supported by electron magnetic resonance measurements.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
