Griffiths-Like Phase in Nanocrystalline Manganite La 0.85 Ca 0.15 MnO 3

The ferromagnetic Curie temperatures TC derived from a temperature derivative of AC susceptibility are equal to 106 K and 161 K for the nanocrystalline and polycrystalline manganites, respectively. The magnetic susceptibility and electron spin resonance confirm that the Griffiths-like phase exists above the Curie temperature in paramagnetic matrix of the nanocrystalline manganite. An analysis of electron spin resonance spectra allows to detect the upper temperature limit for an existence of Griffiths-like phase at temperature TGI = 290 K, which is somewhat higher than the TG of the magnetic susceptibility

Magnetocaloric effect of monovalent K doped manganites Pr0.6Sr0.4−xKxMnO3 (x=0 to 0.2)

peer reviewedMagnetic and magnetocaloric properties are reported for polycrystalline monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3 (x=0, 0.05, 0.1, 0.15 and 0.2) crystallized in orthorhombic structure with Pnma space group. The increasing K content shifts the paramagnetic to ferromagnetic transition temperature from 310 K for x=0 to 269 K for x=0.2. The magnetic entropy change under magnetic field variation of 2 T is found to be 1.95, 3.09, 2.89, 3.05 and 3.2 J/kgK for x varying from 0 to 0.2, respectively. The highest relative cooling power of 102 J/kg is observed for the undoped sample. The sensitivity of magnetic entropy change to magnetic field is estimated by a local N(T) exponent exhibiting the characteristic temperature variation. Phenomenological universal curves of entropy change and Arrott plots confirm the second order phase transition

Magnetocaloric effect in nano- and polycrystalline manganite La0.7Ca0.3MnO3La_{0.7}Ca_{0.3}MnO_3

$La_{0.7}Ca_{0.3}MnO_3$ samples were prepared in nano- and polycrystalline forms by sol-gel and solid state reaction methods, respectively, and structurally characterized by synchrotron X-ray diffraction. The magnetic properties determined by ac susceptibility and dc magnetization measurements are discussed. The magnetocaloric effect in this nanocrystalline manganite is spread over a broader temperature interval than in the polycrystalline case. The relative cooling power of the poly- and nanocrystalline manganites is used to evaluate a possible application for magnetic cooling below room temperature.Comment: 6 pages, 5 (double) figures, 1 table, 16 references; submitted to Appl. Phys.

Magnetocaloric effect in La0.75Sr0.25MnO3 manganite

The polycrystalline manganite La0.75Sr0.25MnO3 prepared by an alternative carbonate precipitation route reveals the rhombohedral perovskite structure. Magnetization isotherms measured up to 2 T are used to determine Curie temperature of 332 K by means of Arrott plot. Maximum of magnetic entropy change is found at Curie temperature. The relative cooling power equal to 64 J/kg for 1.5 T magnetic field, is superior as compared to the manganite with the same chemical composition from the sol–gel method

Effect of nanocrystalline structure on magnetocaloric effect in manganite composites (1/3)La0.7Ca0.3MnO3/(2/3)La0.8Sr0.2MnO3

Poly- and nanocrystalline manganite composites (1/3)La0.7Ca0.3MnO3 and / (2/3)La0.8Sr0.2MnO3 prepared by the sol-gel method are studied by magnetic and transport measurements. The Arrott plots and universal curve of magnetic entropy change confirm that magnetic transition is of the second order. The magnetocaloric effect of polycrystalline composite is found to be roughly twice smaller as compared to the polycrystalline Ca- and Srbased parent phases. The nanocrystalline composite of the same composition exhibits only 8 % reduction of magnetic entropy change. Due to the large temperature spread of magnetocaloric effect the relative cooling power RCP of nanocrystalline composite is about three times larger as compared to the nanocrystalline Ca- and Sr- based parent phases. The maximum magnetic entropy change DSMAX and relative cooling power RCP are found to be more sensitive to magnetic field strength for the nano- than for polycrystalline composites studied

Griffiths-Like Phase in Nanocrystalline Manganite La0.85Ca0.15MnO3La_{0.85}Ca_{0.15}MnO_3

The ferromagnetic Curie temperatures $T_{C}$ derived from a temperature derivative of AC susceptibility are equal to 106 K and 161 K for the nanocrystalline and polycrystalline manganites, respectively. The magnetic susceptibility and electron spin resonance confirm that the Griffiths-like phase exists above the Curie temperature in paramagnetic matrix of the nanocrystalline manganite. An analysis of electron spin resonance spectra allows to detect the upper temperature limit for an existence of Griffiths-like phase at temperature $T_{GI}=290 K$, which is somewhat higher than the $T_{G}$ of the magnetic susceptibility

Magnetic susceptibility and electron magnetic resonance study of monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3

The monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3 (x = 0.05–0.2) are characterized using the complementary magnetic susceptibility and electron resonance methods. In paramagnetic phase the temperature variations of the inverse magnetic susceptibility and the inverse intensity of resonance signal obey the Curie–Weiss law. A similarity in temperature variation of resonance signal width and the adiabatic polaron conductivity points to the polaron mechanism controlling the resonance linewidth. The low temperature limit of the pure paramagnetic phase is determined from the electron resonance spectra revealing the mixed phase spread down to the Curie temperature

Electron Transport in Nanocrystalline Alloys

score: 0collation: 609-61

Critical analysis of the paramagnetic to ferromagnetic phase transition in Pr0.55K0.05Sr0.4MnO3

The critical properties of monovalent doped manganite Pr0.55K0.05Sr0.4MnO3 around the paramagnetic to ferromagnetic phase transition were investigated through various methods: the modified Arrott plots (MAP), the Kouvel-Fisher method and the critical isotherm analysis. Data obtained near Tc were examined in the framework of the mean field theory, the 3D–Heisenberg model, the 3D–Ising model, and tricritical mean field. The deduced critical exponents values obtained using MAP method were found to be β = 0.44(4) with TC ~ 303 K and γ = 1.04(1) with TC ~ 302 K. Kouvel-Fisher method supplies the critical values to be β = 0.41(2) with TC ~ 302 K and γ = 1.09(1) with TC ~ 302 K. The obtained critical parameters show a tendency towards the mean-field behavior, suggesting the existence of long-range ferromagnetic order in the compound studied. The exponent δ deduced separately from isotherm analysis at T= 303 K was found to obey to the Widom scaling relation δ = 1+ γ/ β. The reliability of obtained exponents was confirmed by using the universal scaling hypothesis. The itinerant character of ferromagnetism in the present system was also tested by using Rhodes-Wohlfarth’s criterion

Structural, magnetic and magneto-transport properties of monovalent doped manganite Pr0.55K0.05Sr0.4MnO3

Pr0.55K0.05Sr0.4MnO3 sample have been synthesized using the conventional solid state reaction. Rietveld refinements of the X-ray diffraction patterns at room temperature confirm that the sample is single phase and crystallizes in the orthorhombic structure with Pnma space group; the crystallite size is around 70 nm. The SEM images show that grain size spreads around 1000–1200 nm. DTA analysis does not reveal any clear transition in temperature range studied. The low-temperature DSC indicates that Curie temperature is around 297 K. Magnetization measurements in a magnetic applied field of 0.01 T exhibit a paramagnetic–ferromagnetic transition at the Curie temperature TC = 303 K. A magnetic entropy change under an applied magnetic field of 2 T is found to be 2.26 J kg−1 K−1, resulting in a large relative cooling power around 70 J/kg. Electrical resistivity measurements reveal a transition from semiconductor to metallic phase. The thermal conductivity is found to be higher than that reported for undoped and Na doped manganites reported by Thaljaoui et al. (2013)