Interplay of magnetic sublattices in langite Cu4(OH)6SO4 2H2O

• Published in: New journal of physics Vol. 18; no. 3; pp. 033020 - 33033
• Main Authors: Lebernegg, S, Tsirlin, A A, Janson, O, Redhammer, G J, Rosner, H
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 10.03.2016
• Subjects: 75.50.Ee; Antiferromagnetism; Copper; Couplings; Crystal structure; Crystallography; Crystals; Cu2+-mineral; Ferromagnetism; Flavor (particle physics); frustrated magnet; Heat exchange; Magnetic properties; Magnets; microscopic magnetic model; mineral; Physics; Single crystals; spin-1/2 quantum magnet; Temperature dependence; thermodynamic properties
• ISSN: 1367-2630
• DOI: 10.1088/1367-2630/18/3/033020

Magnetic and crystallographic properties of the mineral langite Cu4(OH)6SO H2O are reported. Thermodynamic measurements combined with a microscopic analysis, based on density-functional bandstructure calculations, identify a quasi-two-dimensional (2D), partially frustrated spin-1/2 lattice resulting in the low Néel temperature of K. This spin lattice splits into two parts with predominant ferro- and antiferromagnetic (AFM) exchange couplings, respectively. The former, ferromagnetic (FM) part is prone to the long-range magnetic order and saturates around 12 T, where the magnetization reaches 0.5 /Cu. The latter, AFM part features a spin-ladder geometry and should evade long-range magnetic order. This representation is corroborated by the peculiar temperature dependence of the specific heat in the magnetically ordered state. We argue that this separation into ferro- and antiferromagnetic sublattices is generic for quantum magnets in Cu2+ oxides that combine different flavors of structural chains built of CuO4 units. To start from reliable structural data, the crystal structure of langite in the 100-280 K temperature range has been determined by single-crystal x-ray diffraction, and the hydrogen positions were refined computationally.