Magnetic behavior of the NixFe1−xNb2O

Abstract

Physical properties of the Ni x Fe 1−x Nb 2 O 6 compounds are investigated combining x-ray and neutron powder diffraction with magnetic and calorimetry measurements as well as 57 Fe Mössbauer spectroscopy. This system is known to present quasi-one-dimensional magnetism with the magnetic moments arranged along weakly interacting Ising chains. Partial substitution of the magnetic ion tends to suppress the magnetic ordering observed in the end members of the series. When this happens, the low-temperature magnetic specific heat agrees well with what is expected for isolated Ising chains. The lowest temperature powder neutron-diffraction patterns exhibit evidence for the occurrence of short-range order, and analysis of these diffuse neutron-scattering patterns allow us to obtain information on the magnetic correlations. The suppression of magnetism is consistently interpreted as resulting from the magnetic-cation disorder induced by substitution, which enhances the system's tendency for frustration of geometrical origin.

Low-dimensional magnetic properties of orthorhombic MnV2O6 : A nonstandard structure stabilized at high pressure

“…Since T N is substantially smaller than θ CW , we have a large frustration index, as indicated in Table II. However, there is no geometric frustration here, in contrast to what was observed for columbites [16,19] with antiferromagnetically coupled FM Ising chains. In the present case, a low T N arises from the (quasi)low dimensionality and isotropy of the spin system, which can only order in three dimensions, so that the scale of T N is determined by the weakest exchange interaction.…”

“…Table II which indicates almost negligible second-order orbital effects. This also means that no significant spin anisotropy should be expected, in contrast to the Ising-like behavior previously observed in other columbites such as (Co/Fe)Nb 2 O 6 [16,17]. Curie-Weiss temperatures are negative, again very similar for the vanadium and niobium orthorhombic compounds, and quite large in absolute values, θ CW = −24.6 K for MnV 2 O 6 and −24.5 K for MnNb 2 O 6 .…”

“…3 at various temperatures. Their behavior is typical of isotropic antiferromagnetism, in contrast to other ANb 2 O 6 orthorhombic systems (A = Fe, Ni), which present Ising-like ferromagnetic chains, and show spin-flip transitions [16,19] in the ordered phase.…”

Quantum magnetism in minerals

“…The noncollinearity of the spin structure is dictated by the direction of the local Ising axis in the distorted AO 6 octahedra. In all of the studied solid solutions with random distribution of the A cations, the non-stoichiometric composition rapidly suppressed long-range magnetic order [236,[239][240][241]. This evidences a substantial drop of the average exchange strength both within and between the chains and a tendency for enhanced frustration among the interchain interactions as a result of disorder.…”

Structural properties and Raman spectra of columbite-type NiNb$_{2-x}$V$_x$O$_6$ synthesized under high pressure

“…Along the c-axis both the octahedra around the Ni and Nb cations form zigzag edge-sharing chains. On the ab-plane the Ni 2+ chains are arranged in an isosceles triangular geometry [2,3] leading to a magnetic behavior of low-dimensional character [3] which is one of the most interesting properties of this compound. Another recently discovered property of the NiNb 2 O 6 is its potential as a photocatalyst under visible light irradiation for the efficient production of H 2 from water splitting [4].…”