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.
We present the ground state properties of a new quantum antiferromagnet, YbBO 3 , in which the isotropic Yb 3+ triangular layers are separated by a nonmagnetic layer of partially occupied B and O(2) sites. The magnetization and heat capacity data establish a spin-orbit entangled effective spin J eff = 1 2 state of Yb 3+ ions at low temperatures, interacting antiferromagnetically with an intralayer coupling J/k B 0.53 K. The absence of oscillations and a 1/3 tail in the zero-field muon asymmetries rules out the onset of magnetic long-range order as well as spin freezing down to 20 mK. An anomalous broad maximum in the temperature-dependent heat capacity with an unusually reduced value and a broad anomaly in the zero-field muon depolarization rate centered at T * 0.7J/k B provide compelling evidence for a wide fluctuating regime (0.2 T /J 1.5) with slow relaxation. We infer that the fluctuating regime is a universal feature of highly frustrated triangular-lattice antiferromagnets while the absence of magnetic long-range order is due to perfect two-dimensionality of the spin lattice protected by nonmagnetic site disorder.
Two new metal cluster (Ni 4 and Co 2 Ni 2 ) based rod shaped micron sized metal-organic frameworks (MOFs) of formulas(compound-2), {OBA = 4,4'-Oxybis(benzoate)} are synthesized via solvothermal technique. Structural, morphological and magnetic properties of both the compounds are characterized using x-ray diffraction, infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and DC magnetization measurements. The homogeneous presence of Co and Ni with a molar ratio of ~1 : 1 in compound-2 is confirmed by EDX elemental mapping analysis. Magnetic measurements reveal that both the compounds are magnetically frustrated due to competing antiferromagnetic (AFM) and ferromagnetic (FM) interactions.Compound-1 has dominant FM while compound-2 has dominant AFM interactions. At low temperatures, magnetic longrange-order sets in, which is identified to be canted FM and canted AFM type for compound-1 and 2, respectively. Below the ordering temperature, multiple magnetic transitions including spin-glass transitions are detected, which can be ascribed to the effect of strong frustration in both the compounds.
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