Persistence of singlet fluctuations in the coupled spin tetrahedra system Cu2Te2O5Br2 revealed by high-field magnetization and 79Br NQR - 125Te NMR

Abstract

We present high-field magnetization and ${}^{79}$Br nuclear quadrupole resonance (NQR) and ${}^{125}$Te nuclear magnetic resonance (NMR) studies in the weakly coupled Cu${}^{2+}$ ($S=1/2$) tetrahedral system Cu${}_2$Te${}_2$O${}_5$Br${}_2$. The field-induced level crossing effects were observed by the magnetization measurements in a long-ranged magnetically ordered state which was confirmed by a strong divergence of the spin-lattice relaxation rate 1/T1 at T0=13.5 K. In the paramagnetic state, 1/T1 reveals an effective singlet-triplet spin gap much larger than that observed by static bulk measurements. Our results imply that the inter- and the intra-tetrahedral interactions compete, but at the same time they cooperate strengthening effectively the local intratetrahedral exchange couplings. We discuss that the unusual feature originates from the frustrated intertetrahedral interactions.

5 pages, 4 figures, accepted in Phys. Rev. B as a Rapid Communications

References in corpus (3)

• Quantum Magnets under Pressure: Controlling Elementary Excitations in TlCuCl3
• Anomalous frequency and intensity scaling of collective and local modes in a coupled spin tetrahedron system
• Anisotropic field dependence of the magnetic transition in Cu2Te2O5Br2

Cited by in corpus (1)

• Unusual spin pseudogap behavior in the spin web lattice Cu${}_3$TeO${}_6$ probed by ${}^{125}$Te nuclear magnetic resonance