Structural invariance upon antiferromagnetic ordering in geometrically frustrated swedenborgite, CaBaCo₂Fe₂O₇

Abstract

Centimetre-sized single crystals of high-quality CaBaCo 2 Fe 2 O 7 were synthesized by the optical floating zone technique. The metal-to-metal stoichiometry and oxygen content were confirmed by spectroscopy and thermal reduction experiments. The hexagonal symmetry P6 3 mc (No. 186) well describes the powder X-ray and neutron diffraction as well as single-crystal neutron diffraction at all measured temperatures. This symmetry is also consistent with optical second harmonic generation data obtained between 10 and 295 K. However, a satisfactory structure description from single-crystal neutron diffraction data needs an oxygen split position. Specific heat, magnetic susceptibility and powder neutron diffraction data indicate a magnetic phase transition at T N = 159 K to an antiferromagnetic ground state, but with a persisting hexagonal symmetry and intrinsic geometric frustration.research papers

Neutron diffraction study and theoretical analysis of the antiferromagnetic order and the diffuse scattering in the layered kagome system CaBaCo2Fe2O7

“…The single crystal specimen, 0.03 ccm and 2 ccm, for magnetization measurements and neutron diffraction experiments respectively, were synthesized using the same method described previously in detail 14 .…”

“…12,13 The compound CaBaCo 2 Fe 2 O 7 studied in this work is the only swedenborgite reported so far that shows a three-dimensional long range AFM order within the ideal hexagonal structure. 14 In the first approximation, swedenborgites can be described by a Heisenberg model with only two exchange interactions between classical spins: J in (between the nearestneighbor spins in the Kagome plane) and J out (between the neighboring Kagome and triangular sites). For a suitable choice of the ratio τ = J out /J in , this model provides a good description of the observed diffuse scattering in YBaCo 4 O 7 9 and reveals a variety of partially ordered and disordered ground states originating from the geometric frustration of the swedenborgite lattice structure.…”

Mag2Pol: a program for the analysis of spherical neutron polarimetry, flipping ratio and integrated intensity data

“…The swedenborgite family is a compound class with a large variety of physical properties [ranging from long-range magnetic order (Reim et al, 2014) to spin-glass (Valldor & Andersson, 2002;Valldor, 2004) and spin-liquid behavior (Valldor, 2006;Schweika et al, 2007;Valldor et al, 2011)], which is a result of the geometrical frustration in this layered kagome system and the type of distortion relieving it. CaBa-Co 3 FeO 4 is observed to have an orthorhombic crystal structure and orders antiferromagnetically below T N ' 140 K (Valldor et al, 2009).…”

Swedenborgite CaBa(Mn2Fe2)O7 with Spin Ordering on a Geometrically Frustrated, Polar, Non‐centrosymmetric S = 5/2 Lattice

“…The predicted electric polarity is reported to be relatively strong and non‐linear optic activity were observed in CaBa(Co 2 Fe 2 )O 7 , as revealed by its second‐harmonic‐generation effect …”