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

Abstract

Magnetic and crystallographic properties of the mineral langite Cu 4 (OH) 6 SO 2 4 · H 2 O 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 T 5.7 N  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 B m /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 Cu 2+ oxides that combine different flavors of structural chains built of CuO 4 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.chains develop incommensurate spin correlations and helical magnetic order [8,9], although few instances of FM intrachain spin order are known as well [10,11]. The helical spin arrangement observed in simple binary compounds CuCl 2 [12] and CuBr 2 [13] and in more complex materials like linarite PbCu(OH) 2 SO 4 [14], all being frustrated J J 1 2 spin chains, may trigger electric polarization induced by the magnetic order, thus leading to multiferroic behavior [15-18]. Additionally, small interactions beyond the isotropic Heisenberg model lead to an intricate magnetic phase diagram, including multipolar (three-magnon) phases, which has been studied recently [19]. However, the complex interplay of frustration and anisotropy needs further investigations on different systems as, e.g., LiCuVO 4 [20-23]. One may naturally ask what happens when two types of spin chains, those with edge-and corner-sharing geometries, are placed next to each other within one material. Spin systems comprising several magnetic OPEN ACCESS RECEIVED =. A more detailed description of the procedure can be found, e.g., in [31,54]. Alternatively, strong electron correlations are added on top of LDA by the LSDA+U method in a mean-field way and are thus included in the self-consistent procedure. This allows for calculating total exchange constants J J J ij ij ij FM AFM ( ) m = J J J 81

Frustrated spin chain physics near the Majumdar-Ghosh point in szenicsiteCu3(MoO4)(OH)4

“…The same argument applies to t D , comprising a very similar out-ofplane position of H. This hopping would also increase to t D = −227 meV for the hypothetical in-plane position of H. Thus, both NN transfer integrals in the side chain increase by almost the same amount of about 100 K when hydrogens are moved in-plane. This tendency of an out-of-plane position of H suppressing the transfer probability agrees with our previous studies on Cu 2+minerals 47,51,63 .…”

Quantum magnetism in minerals

“…This may be partly due to the metastability of both posnjakite and wroewolfeite phases, which readily lose water and are converted to brochantite under unfavourable conditions [595,596]. Meanwhile, the langite structure has been recently addressed by Lebernegg et al [597]. Its magnetic layers contain four structurally inequivalent Cu sites, of which Cu(1) and Cu(2) form slightly buckled corner-sharing CuO 4 chains, whereas Cu(3) and Cu(4) form linear edge-sharing CuO 4 chains.…”

“…J h with different signs, so that the chains are not independent but form part of a complex 2D magnetic network. Specific-heat and magnetization data indicate that the spin lattice of langite splits into two sublattices with predominantly FM and AFM couplings at low temperatures [597]. The former develops long-range magnetic order with a saturation field of ∼ 12 T, whereas…”

Magnetism of coupled spin tetrahedra in ilinskite-type KCu5O2(SeO3)2Cl3

“…Given persistent interest in theoretical studies of the sawtooth (delta) chains [14][15][16][17] and low-dimensional frameworks of spin tetrahedra [18][19][20][21][22][23], as well as the dearth of relevant model materials, we chose to explore magnetic behavior of KCu 5 O 2 (SeO 3 ) 2 Cl 3 and elucidate its interaction topology. To this end, we combine experimental probes with extensive first-principles calculations, because magnetic interactions in Cu-based minerals are far from trivial [24][25][26][27], and KCu 5 O 2 (SeO 3 ) 2 Cl 3 is no exception.…”