Search

Considering the fact that solid-state refrigerants have attracted great attention, we report here the studies related to the magnetic phase transition and magnetocaloric effect (MCE) of electron-doped La 1− x Zr x MnO 3 ( x = 0.05, 0.10 and 0.15) samples synthesized by solid-state reaction. It is observed that there is an increase in magnetization with an increase in Zr doping up to x = 0.15. The isothermal magnetization versus applied magnetic field was used to calculate the magnetic entropy change ǀΔS m ǀ for La 1− x Zr x MnO 3 ( x = 0.05, 0.10 and 0.15) at varying temperatures (100–300 K). Increase in ǀΔS m ǀ value from 0.6 J kg −1 K −1 to 2.08 J kg −1 K −1 is noted with increase in Zr doping from x = 0.05 to x = 0.15, respectively. The relative cooling power (RCP) value of La 0.85 Zr 0.15 MnO 3 is found to be 142.50 J kg −1 at H = 50 kOe and is comparable with earlier reported MCE compounds. Furthermore, Banerjee's criteria and Landau theory of phase transitions were also studied to access magnetic ordering in the samples. [ABSTRACT FROM AUTHOR]

Abstract: The structural and the magnetic properties of Nd0.5Sr0.5MnO3 films with column-like nano-clustered microstructure have been investigated. The high-resolution electron microscopy, X-ray diffraction and electron diffraction reveal that the average cluster diameter was about 10nm, and that the charge-ordered state, typical for this composition, was not observed down to 87K. The films manifest a superparamagnetic behavior with increasing temperature, and an additional antiferromagnetic transition at T N⩽50K. The analysis of the temperature-dependent magnetization shows that an increase in the applied magnetic field from 0.01 to 1T leads to a drastic decrease from 3000 to 150μ B in the effective magnetic moment of superparamagnetic particles, which is simply described by μ eff∼1/H. Therefore, the superparamagnetic particles in these films are not rigidly bound with the crystalline clusters and the size is controlled by applied magnetic field. The greatly asymmetric hysteresis loops at low temperatures are explained by the exchange-bias interaction between the ferro- and the antiferro-magnetic clusters. [Copyright &y& Elsevier]

Abstract: A series of polycrystalline samples of La1−x Sr x MnO3 (x =0.1, 0.2 and 0.3) have been synthesized by combustion route. These samples have been characterized structurally, morphologically and magnetically by X-ray diffraction, scanning electron microscopy and SQUID, respectively. The order of magnetic phase transition is revealed to be the second order from ferromagnetic to paramagnetic state. The maximum magnetic entropy changes (ΔS M), calculated from the M–H measurements, is 0.13, 0.16 and 0.20J/kgK for La0.9Sr0.1MnO3, La0.8Sr0.2MnO3 and La0.7Sr0.3MnO3, respectively. [Copyright &y& Elsevier]

Abstract: Ferromagnetic resonance has been studied in the flash-evaporated Co2MnGa Heusler alloy (HA) films with different structural order. Depending on annealing temperature, varied from 293 to 728K, the films are amorphous, fine crystalline with A2 (or B2) type of structure or ordered with L21 structure. The amorphous films are weakly magnetic and inhomogeneous with the saturation magnetization M S∼25G at room temperature (RT) and with the magnetic regions having the effective magnetization M eff≈200–300G. The L21-ordered films are ferromagnetic with the Curie temperature of 650K and M S (RT)≈450G≈2.5 μ B f.u. (lower than the bulk value of 4 μ B) and M eff (RT)=500–550G. The temperatures of ordering from the amorphous to A2 (B2) structure and from A2 (B2) to L21 structure are estimated to 430 and 550K, respectively. [Copyright &y& Elsevier]

The ordered and disordered Ni2MnGa alloy films were prepared by using the flash-evaporation technique. The structure and the temperature dependence of the transport and magnetic properties of the films were investigated. Unexpectedly, the disordering in Ni2MnGa alloy films does not lead to any appreciable magnetic ordering down to 4 K. An annealing of the disordered films restores the ordered structure with an almost full recovery of the magnetic and the transport properties of the ordered alloy films. [Copyright &y& Elsevier]

Abstract: We fabricated two-dimensional (2-D) Co magnetic arrays starting from a 40-nm-thick Co layer on a 6-in. Si wafer by photolithography with a KrF laser source and the wet-etching process. Various patterns, including square and triangular lattices, were achieved, with their smallest feature size ranging from 300 to 800nm. In this paper, we present the key processes to prepare nano-scaled 2-D magnetic arrays and the fabricated structures, along with their magnetic properties. [Copyright &y& Elsevier]

Abstract: Mn-doped ZnO films (for Mn at% ∼4%) were implanted using 30keV H+ ions with a dose of 6.9×1016 cm–2 and subsequently annealed at 300°C to study the effect of magnetism on the interstitial hydrogen in n-type II–VI magnetic semiconductors by using secondary ion mass spectroscopy (SIMS), Hall measurement and SQUID. We observed that the interstitial hydrogen leads to the changes in the magnetic hysteresis loop as well as the enhancement of carrier concentrations in the Mn-doped ZnO film. [Copyright &y& Elsevier]