The crystal structure and magnetic ordering pattern of PdAs 2 O 6 were investigated by neutron powder diffraction. While the magnetic structure of PdAs 2 O 6 is identical to the one of its isostructural 3d-homologue NiAs 2 O 6 , its Néel temperature (140 K) is much higher than the one of NiAs 2 O 6 (30 K). This is surprising in view of the long distance and indirect exchange path between the magnetic Pd 2+ ions. Density functional calculations yield insight into the electronic structure and the geometry of the exchange-bond network of both PdAs 2 O 6 and NiAs 2 O 6 , and provide a semi-quantitative explanation of the large amplitude difference between their primary exchange interaction parameters.

We report the synthesis and characterization of the new bismuth iron selenite oxochloride Bi2Fe(SeO3)2OCl3. The main feature of its crystal structure is the presence of a reasonably isolated set of spin S = 5/2 zigzag chains of corner-sharing FeO6 octahedra decorated with BiO4Cl3, BiO3Cl3, and SeO3 groups. When the temperature is lowered, the magnetization passes through a broad maximum at Tmax ≈ 130 K, which indicates the formation of a magnetic short-range correlation regime. The same behavior is demonstrated by the integral electron spin resonance intensity. The absorption is characterized by the isotropic effective factor g ≈ 2 typical for high-spin Fe(3+) ions. The broadening of ESR absorption lines at low temperatures with the critical exponent β = 7/4 is consistent with the divergence of the temperature-dependent correlation length expected for the quasi-one-dimensional antiferromagnetic spin chain upon approaching the long-range ordering transition from above. At TN = 13 K, Bi2Fe(SeO3)2OCl3 exhibits a transition into an antiferromagnetically ordered state, evidenced in the magnetization, specific heat, and Mössbauer spectra. At T < TN, the (57)Fe Mössbauer spectra reveal a low saturated value of the hyperfine field Hhf ≈ 44 T, which indicates a quantum spin reduction of spin-only magnetic moment ΔS/S ≈ 20%. The determination of exchange interaction parameters using first-principles calculations validates the quasi-one-dimensional nature of magnetism in this compound.

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