A series of disordered Ca1.5La0.5FeRuO6, CaLaFeRuO6 and La2FeRuO6 double perovskites was prepared by solid-state method and investigated by neutron powder diffraction, x-ray absorption near edge structure (XANES) analysis at the...
The structural and magnetic properties of the square-cupola antiferromagnet Sr(TiO)Cu4(PO4)4 are investigated via x-ray diffraction, magnetization, heat capacity, and 31 P nuclear magnetic resonance experiments on polycrystalline samples, as well as density-functional band-structure calculations. The temperature-dependent unit cell volume could be described well using the Debye approximation with the Debye temperature of θD 550 K. Magnetic response reveals a pronounced two-dimensionality with a magnetic long-range-order below TN 6.2 K. High-field magnetization exhibits a kink at 1/3 of the saturation magnetization. Asymmetric 31 P NMR spectra clearly suggest strong in-plane anisotropy in the magnetic susceptibility, as anticipated from the crystal structure. From the 31 P NMR shift vs bulk susceptibility plot, the isotropic and axial parts of the hyperfine coupling between 31 P nuclei and the Cu 2+ spins are calculated to be A iso hf 6539 and A ax hf 952 Oe/µB, respectively. The low-temperature and low-field 31 P NMR spectra indicate a commensurate antiferromagnetic ordering. Frustrated nature of the compound is inferred from the temperature-dependent 31 P NMR spin-lattice relaxation rate and confirmed by our microscopic analysis that reveals strong frustration of the square cupola by next-nearest-neighbor exchange couplings.
Correlation of molecular structure and its magnetic property gives a better understanding toward the design of magnetic materials with long-range magnetic order. Here we report two new cobalt-based coordination polymers that exhibited coexistence of long-range ferromagnetic (FM) order and spin-glass (SG) transition at below T c . Different orientation of magnetic moments, arrangements, and variation in connectivity with the ligands might be responsible for the SG transition. The SG transition was characterized by bifurcation of zero-field-cooled and field-cooled splitting at T f ≈ 9.9 K (for both compounds) and AC susceptibility measurements. DC magnetization revealed the FM transition at high temperature, followed by a low-temperature SG transition. Moreover, the peculiarity found in low-temperature χ′′(T) can be attributed to the complex interplay between antiferromagnetic and ferromagnetic interactions and the coexistence of the long-range FM order and SG phase. Optical bandgap and temperature-dependent resistivity measurements showed that these compounds are semiconducting in nature.
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