The magnetization behavior and spin configurations of anisotropic triangular spin-chain systems are investigated using Monte Carlo simulations based on two-and three-dimensional Ising models, in order to understand the fascinating magnetic phenomena observed in Ca 3 Co 2 O 6 compound. By taking into account the strong intrachain ferromagnetic interaction and relatively weak interchain antiferromagnetic interaction, the simulations reproduce quantitatively the temperature-dependent magnetization behaviors against external magnetic field at low temperature. We present the one-to-one correspondence between the magnetizations and the nearest-neighboring pattern-count/spin snapshots, and demonstrate that the steplike magnetizations are ascribed to the inhomogeneous in-plane spin configurations and ferrimagnetically ordered equilibrium state. It is indicated that for the multistep magnetizations that appeared at low temperature, the substeps are always equidistant and the interval of critical magnetic field for spin flip keeps on 1.2 T. However, the inhomogeneity of the spin configurations makes a mean field approach to the magnetization behavior unsuccessful in predicting the multistep magnetizations.
The dependence of magnetotransport behaviors on A-site disorder induced by A-site cational size mismatch in ferromagnetic manganites is investigated by characterizing a series of samples with the same A-site cational mean radius ͗r A ͘ = 1.20 Å but different A-site ionic radii variance 2 = ͚ i x i r i 2 − ͗r A ͘ 2 , where x i and r i are the atomic fraction and ionic radii of i-type ions at A-site, respectively. It is revealed that the ground state transits from ferromagnetic metal to cluster-glass insulator upon increasing the variance 2 from 0.0003 for La 0.55 Ca 0.45 MnO 3 to 0.015 for Sm 0.55 ͑Ca 0.6 Ba 0.4 ͒ 0.45 MnO 3 , while the crystallographic structure and lattice constants of these manganites remain unchanged. Nevertheless, the increasing A-site disorder is believed to enhance the random local radial distortion of MnO 6 octahedra and suppress the ferromagnetic long-range order. In the manganites of high A-site disorder, the long-range ferromagnetic ordering is completely melted into the short-range magnetically ordered clusters and then the stepwise magnetization. With decreasing temperature, the short-range ordered clusters become frustrated at the frustrating point, below which a cluster-glass transition occurs due to the weak intercluster interaction.
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