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Samples with inversion parameter values (δ) ranging from 0.27 to 0.14 while maintaining the crystallite size value have been successfully fabricated from commercially available powders by mechanical grinding and thermal annealing treatments at temperatures ranging between 400 and 600 °C. Detailed characterization studies of these samples using X-ray, neutron diffraction and magnetic measurements have confirmed for the first time the simultaneous coexistence at 2 K of short range antiferromagnetic and ferrimagnetic ordering for a wide range of the inversion parameter. The magnetic phase diagram obtained is different from the one previously reported, which shows at 2 K the coexistence of long range antiferromagnetic order and short range order for values of inversion parameters less than 0.1 and the presence of a ferrimagnetic order only for values of δ > 0.2. At room temperature, the Rietveld analysis of NPD patterns and the magnetization curves showed a paramagnetic behavior in the samples with δ ≤ 0.1. For the samples with higher cationic inversion, typical hysteresis curves of ferrimagnetic materials were observed and the saturation magnetization values obtained agree quite well with the net magnetic moment obtained from the Rietveld refinement of the neutron diffraction patterns. [ABSTRACT FROM AUTHOR]

Polycrystalline sample of Bi 2 Cu 5 B 4 O 14 was synthesized and its structural and magnetic properties were investigated by means of temperature dependent x-ray diffraction, magnetization, and heat capacity measurements. Bi 2 Cu 5 B 4 O 14 is found to be a spin-1/2 layered compound with repeating Cu-pentamer units. DC magnetic susceptibility at high temperatures follows the Curie-Weiss law with a large and negative Curie-Weiss temperature θ CW ≃ −39 K, suggesting the dominant ferromagnetic interaction between Cu 2+ ions. A positive curvature in inverse susceptibility and a magnetization hysteresis with reduced ordered moment at T = 2.1 K pinpoint the ferrimagnetic nature of the compound with T C ≃ 25 K. The modified Arrott analysis shows that Bi 2 Cu 5 B 4 O 14 is a good example of Heisenberg ( β = 0.367 and γ = 1.388) ferrimagnet. Heat capacity data at low temperatures (i.e. in the ordered state) follows a power law ( γT α ) with a reduced exponent ( α ≃ 2.58). The change in magnetic entropy is calculated to be S mag ≃ 28 J/mol K at around 100 K which is close to the expected theoretical value of 28.81 J/mol K for Bi 2 Cu 5 B 4 O 14 . [ABSTRACT FROM AUTHOR]

The synthesis, structural characterization, and magnetic properties of La 3 Mn 2 NbO 9 double perovskite are reported. The crystal structure has been refined by X-ray and neutron powder diffraction data in the monoclinic space group P2 1 /n. The Mn2+, Mn3+ and Nb5+ cations are distributed at the 2d and 2c Wyckoff sites, with a high cation order degree in the latter, mainly occupied by Mn2+/Mn3+. The Mn3+ presence was established from X-ray Emission Spectroscopy and X-ray Photoelectron Spectroscopy. Rietveld refinements of powder neutron diffraction data show that at room temperature the cell parameters are a= 5.6063(3) Å, b= 5.8155(3) Å, c= 7.9877(2) Å y β= 89.89(1)°. Magnetization measurements indicate the presence of ferromagnetic and antiferromagnetic interactions with T C ∼19 K and T N ∼11 K, respectively, with a magnetic cell of symmetry Γ 1 (A g). The analysis of the neutron data suggests a canted ferrimagnetic spin structure where an antiferromagnetic unit-cell in a and c axis, and ferromagnetic in b axis with a propagation vector k = (0 ½ 0) was used. The effective magnetic moment obtained experimentally is μ eff = 5.50 μ B /mol Mn2+/3+, slightly lower than the theoretical one for spin only (5.83 μ B). • Synthesis of new double perovskite La 3 Mn 2 NbO 9. • Canted ferrimagnetism due to the high degree of structural distortion. • Effective existence of Mn2+/Mn3+ mixture. • Multiple possible magnetic interactions and huge distortion of the octahedral network allow AFM and FM couplings. [ABSTRACT FROM AUTHOR]