Magnetization and spin dynamics of the spinS=12hourglass nanomagnet Cu5(OH)

Abstract

We report a combined experimental and theoretical study of the spin S = 1 2 nanomagnet Cu5(OH)2(NIPA)4•10H2O (Cu5-NIPA). Using thermodynamic, electron spin resonance and 1 H nuclear magnetic resonance measurements on one hand, and ab initio density-functional band-structure calculations, exact diagonalizations and a strong coupling theory on the other, we derive a microscopic magnetic model of Cu5-NIPA and characterize the spin dynamics of this system. The elementary five-fold Cu 2+ unit features an hourglass structure of two corner-sharing scalene triangles related by inversion symmetry. Our microscopic Heisenberg model comprises one ferromagnetic and two antiferromagnetic exchange couplings in each triangle, stabilizing a single spin S = 1 2 doublet ground state (GS), with an exactly vanishing zero-field splitting (by Kramer's theorem), and a very large excitation gap of ∆ 68 K. Thus, Cu5-NIPA is a good candidate for achieving long electronic spin relaxation (T1) and coherence (T2) times at low temperatures, in analogy to other nanomagnets with low-spin GS's. Of particular interest is the strongly inhomogeneous distribution of the GS magnetic moment over the five Cu 2+ spins. This is a purely quantum-mechanical effect since, despite the non-frustrated nature of the magnetic couplings, the GS is far from the classical collinear ferrimagnetic configuration. Finally, Cu5-NIPA is a rare example of a S = 1 2 nanomagnet showing an enhancement in the nuclear spin-lattice relaxation rate 1/T1 at intermediate temperatures.

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

“…Therefore, the FM couplings occur between less twisted plaquettes, whereas the AFM coupling takes place between the more twisted plaquettes, and, in contrast to ref. 44 , the twisting does not enhance ferromagnetism. We thus conclude that side groups should be at play here.…”

“…For example, the superexchange between the orthogonal CuO 4 plaquettes can remain FM even if the Cu–O–Cu angle departs from 90° reaching 100–105°  44 . One may suggest that this trend persists at higher bridging angles, as observed in KCu 5 O 2 (SeO 3 ) 2 Cl 3 .…”

Frustration and Dzyaloshinsky-Moriya anisotropy in the kagome francisitesCu3Bi(SeO3)2ORousochatzakis1, Richter2, Zinke3 et al. 2015Phys. Rev. B524682View full textAdd to dashboardCite

“…28 Remarkably, the isotropic couplings J i are nearly the same in the Cl and Br compounds. This similarity is rooted in their very similar crystal structures 12 and in the minor contribution of halogen p-states to the Cu d x 2 −y 2 bands at the Fermi level, see Fig.…”

“…In both codes, the Perdew-Burke-Ernzerhof flavor of the exchange-correlation potential corresponding to the generalized gradient approximation (GGA) has been used 25 . Strong correlations in the Cu 3d shell were treated on the mean-field level using the GGA+U approach with the on-site Coulomb repulsion parameter U d = 9.5 eV and Hund's exchange J d = 1 eV [26][27][28] .…”

Quasi-two-dimensionalS=12magnetism ofCu[C6H2(<

“…21,22 All calculations were performed for the experimental crystal structure with the positions of hydrogen atoms fully relaxed within GGA.…”