Y. P. Sun

Magnetocaloric effect and Griffiths-like phase in La0.67Sr0.33MnO3 nanoparticles

The effect of grain size on electrical and magnetic properties of La0.67Sr0.33MnO3 nanoparticles with average grain size 32–85 nm has been investigated. The metal-insulator transition temperature TP gradually decreases with decreasing grain size, while the ferromagnetic-paramagnetic transition temperature TC remains almost constant. For the 32 nm sample, the larger effective magnetic moments and the deviation of the inverse susceptibility from the Curie–Weiss law are observed, indicating the possible existence of a Griffiths-like cluster phase. The ferromagnetic transition of the samples is further investigated by measuring magnetocaloric effect (MCE). The presence of short-range magnetic order greatly depresses the magnetic entropy of the paramagnetic phase. Moreover, the analysis of the MCE using Landau theory of phase transition confirms the importance of magnetoelastic coupling and electron interaction in magnetocaloric properties of manganites.

Magnetic properties and magnetocaloric effect of La0.8Ca0.2MnO3 nanoparticles tuned by particle size

La0.8Ca0.2MnO3 particles with the sizes from 17 to 43 nm have been prepared using the sol-gel method and the magnetic properties are systematically studied. The existence of the blocking of the superparamagnetism (SPM), freezing of super-spin-glass, and surface-spin-glass is evidenced. It is found that a core-shell structure can be responsible for the magnetism behavior of the nanoparticles. The phase transition from paramagnetism (PM) to ferromagnetism (FM) is modified from first order to second order as the particle size reduced. The magnetocaloric effect (MCE) thus is modified by the changed magnetism. The observed temperature interval of the magnetic entropy change broadens as the particle size reduced. The magnetic entropy change of superparamagnetic particles has been calculated based on the core-shell model. The relative cooling power (RCP) can be tuned dramatically by particle size due to the change of spontaneous magnetization of the core and the changed ratio of the shell and surface, which show...

Fe-doping–induced superconductivity in the charge-density-wave system 1T-TaS2

We report the interplay between charge-density-wave (CDW) and superconductivity of 1T-FexTa1−xS2 (0≤x≤0.05) single crystals. The CDW order is gradually suppressed by Fe-doping, accompanied by the disappearance of pseudogap/Mott-gap as shown by the density functional theory (DFT) calculations. The superconducting state develops at low temperatures within the CDW state for the samples with the moderate doping levels. The superconductivity strongly depends on x within a narrow range, and the maximum superconducting transition temperature is 2.8 K as x=0.02. For high doping level (x> 0.04), the Anderson localization (AL) state appears, resulting in a large increase of resistivity. We present a complete electronic phase diagram of the 1T-FexTa1−xS2 system that shows a dome-like Tc(x).

AlNxMn3 A possible high-temperature soft magnetic material and strongly correlated system

Structural, magnetic, electrical, and thermal transport properties of antiperovskite compounds AlNxMn3 (x=1,1.1,1.2) have been investigated systematically. With increasing x, the lattice constant increases monotonously while the Curie temperature TC decreases. Both the high TC and small coercive fields consistently indicate AlNxMn3 may be a promising high-temperature soft magnetic material. The resistivity displays T2-dependence below 30 K and the Kadowaki–Woods ratio is about 107.7u2002μΩu2009cm/K2, indicating a possible strongly correlated Fermi-liquid behavior in AlNMn3. Further analysis suggests that the electron-type carriers are dominant and the thermal conductivity mainly originates from the lattice contribution.

Role of nitrogen in AlNxMn3: A density functional theory study

Recently, we successfully synthesized the nitrogen-deficient manganese antiperovskites AlNxMn3 with the very high ferromagnetic Curie temperatures TC up to 818u2009K [Lin et al., Appl. Phys. Lett. 98, 092507 (2011)]. In order to figure out the role of nitrogen for the magnetism, in the present work, we performed a theoretical investigation on AlNxMn3 through the first-principles calculation based on density functional theory. The results show that AlNxMn3 have the ferromagnetic ground states, and the total magnetic moments in a cell are enhanced with decreasing the nitrogen concentration. Based on the calculations of band structure and density of states, we showed the influence of nitrogen concentration on magnetism for AlNxMn3: The decreasing of nitrogen concentration from ideal AlNMn3 moves the spin-down bands towards the high energy remarkably, which enhances the exchange splitting energy ΔEex; on the other hand, nitrogen deficiency reduces the Mn-N hybridizations, which makes the 3d electrons of Mn tend t...

Structural, Elastic, and Electronic Properties of Antiperovskite Chromium-Based Carbides ACCr3 (A = Al and Ga)

We theoretically investigated antiperovskite chromium-based carbides ACCr3 through the first-principles calculation based on density functional theory (DFT). The structure optimization shows that the lattice parameter of ACCr3 is basically proportional to the radius of A-site elements. The calculated formation energies show that AlCCr3 and GaCCr3 can be synthesized at ambient pressure and are stable with nonmagnetic ground states. Based on the calculation of elastic constants, some elastic, mechanical, and thermal parameters are derived and discussed. AlCCr3 and GaCCr3 show ductile natures and may have similar thermal properties. From the analysis of the electronic structures, it was found that there are electron and hole bands that cross the Fermi level for AlCCr3 and GaCCr3, indicating multiple-band natures. The Fermi level locates at the vicinity of the density of states (DOSs) peak, which leads to a large DOS at Fermi level dominated by Cr-3d electrons. The band structures of AlCCr3 and GaCCr3 are very similar to those of the superconducting antiperovskite MgCNi3. The similarity may make AlCCr3 and GaCCr3 behave superconductively, which needs to be further investigated in theoretical and experimental studies.

The Magnetic/Electrical Phase Diagram of Cr-Doped Antiperovskite Compounds GaCFe3−xCrx (0 《 x《0.9)

We report the effect of Cr doping on the structural, magnetic, and electrical transport properties in Cr-doped antiperovskite compounds (). With increasing the Cr content , the lattice constant increases while both the Curie temperature and the saturated magnetization decrease gradually. The electrical resistivity shows different behaviors as a function of . For , there exists a semiconductor-like behavior below a certain temperature which decreases with increasing . In contrast, for , the resistivity shows a metallic behavior in the whole temperature measured (2–350u2009K). In particular, the Fermi-liquid behavior is obtained below 70u2009K. Finally, based on the magnetic and electrical properties of () a magnetic/electrical phase diagram was plotted.