D.N. Shi

Critical behavior and long-range ferromagnetic order in perovskite manganite Nd0.55Sr0.45MnO3

The critical behavior of perovskite manganite Nd0.55Sr0.45MnO3 has been investigated based on the static magnetization measurement around the paramagnetic-ferromagnetic transition temperature 273 K. A large critical exponent and a small one have been obtained by calculating the magnetic-field dependence of the magnetic-entropy change and the Widom scaling relation. These critical exponents not only obey the scaling hypothesis, but also corroborate the results obtained from the Kouvel-Fisher method. In comparison with the values given by standard models, these obtained exponents are very close to those expected from the mean-field model ( and ) and its magnetic-coupling type belongs to nearly long-range interaction. We suggest that the A-site spin disorder and localized magnetic phase competition are the main reasons for the actual critical exponents to show a slight deviation from the theoretical model.

Magnetic entropy change and accurate determination of Curie temperature in single-crystalline helimagnet FeGe

Cubic helimagnet FeGe has emerged as a class of skyrmion materials near room temperature that may impact future information technology. Experimentally identifying the detailed properties of skyrmion materials enables their practical application acceleratedly. Here we study the magnetic entropy change (MEC) of single-crystalline FeGe in its precursor region and clarify its close relation to the critical exponents of a second-order phase transition in this area. The maximum MEC is found to be 2.86 J/kg K for a 7.0 T magnetic-field change smaller than that of common magnetocaloric materials indicating the multiplicity and complexity of the magnetic structure phases in the precursor region. This result also implies that the competition among the multimagnetic phases can partly counteract the magnetic-field–driven force and establishes a stable balance. Based on the obtained MEC and the critical exponents, the exact Curie temperature of single-crystalline FeGe under zero magnetic field is confirmed to be 279.1 K, higher than the previously reported 278.2 K. This finding paves the way for reconstruction of the FeGe phase diagram in the precursor region.

Scaling of disordered recursive scale-free networks

In this paper, we present a solvable model of disordered recursive scale-free networks. The structure, fractality, and dimensionality are studied theoretically and numerically, which are shown to be totally different from those in ordered recursive networks. The transfinite fractal (transfractal) dimension, which is recently introduced to distinguish the structural differences between the networks with infinite dimension, exhibits an interesting scaling behavior. We also investigate the diffusion process on this family of networks, and it is found that the transfractal dimension can identify detailed scaling behavior of diffusion dynamics on transfractal networks.

Synthesis and magnetostrictive properties of Pr1−xDyx(Fe0.8Co0.2)1.93 cubic Laves compounds

The structure, magnetic properties and magnetostriction of high-pressure synthesized Pr1−xDyx(Fe0.8Co0.2)1.93 compounds were investigated. These compounds, which could not be readily synthesized under ambient pressure, exhibit single cubic Laves phase owing to the effects of high-pressure annealing. The Curie temperature increases with increasing x, indicating that 3d-4f coupling becomes stronger with the increase of Dy concentration. The saturation magnetization decreases with increasing x, which can be ascribed to the competition of sublattice magnetization. The easy magnetization direction of the compound lies along with x ≤ 0.05 while lies along when x ≥ 0.10. Meanwhile, the low-field magnetostriction λ∥ − λ⊥ of the compound system peaks at x = 0.05 and then decreases with increasing x, which reveals that the composition anisotropy compensation between Pr3+ and Dy3+ might be realized in Pr1−xDyx(Fe0.8Co0.2)1.93 system. Pr0.95Dy0.05(Fe0.8Co0.2)1.93 compound combines a large low-field magn...

Variation of exchange energy in δ-(Ga,Mn)As films under tensile strain: PBE and LDA+U calculations

PBE and LDA+U calculations were both used to clarify the variation of exchange energy in three kinds of δ-(Ga,Mn)As films under tensile strain. All configurations were strong FM types regardless of which of the two methods was used under strain. Tensile strain could affect the exchange energy and the thickness of three kinds of films. In some configurations, the exchange energy could be enhanced by shape deformation. The thickness of δ-(Ga,Mn)As from LDA+U calculations was greater than from PBE with the same lattice constant in each structure. PBE showed strong double exchange, while LDA+U resulted in a p–d exchange between Mn atoms in the DOS structure. All such films could be grown layer-by-layer based on the formation energy thereof.