Low-field spin dynamics of Cr7Ni and Cr7Ni−Cu−Cr7Ni molecular rings as detected by μSR

Journal article

Muon spin rotation measurements were used to investigate the spin dynamics of heterometallic Cr 7 Ni and Cr 7 Ni-Cu-Cr 7 Ni molecular clusters. In Cr 7 Ni the magnetic ions are arranged in a quasiplanar ring and interact via an antiferromagnetic exchange coupling constant J, while Cr 7 Ni-Cu-Cr7Ni is composed of two Cr7Ni linked by a bridging moiety containing one Cu ion, that induces an inter-ring ferromagnetic interaction J ≪ J. The longitudinal muon relaxation rate λ collected at low magnetic fields μ0H < 0.15 Tesla, shows that the two systems present differences in spin dynamics vs temperature. While both samples exhibit a main peak in the muon relaxation rate vs temperature, at T ∼ 10Kfor Cr 7 Ni and T ∼ 8KforCr 7 Ni-Cu-Cr 7 Ni, the two compounds have distinct additional features: Cr7Ni shows a shoulder in λ(T ) for T < 8 K, while Cr 7 Ni-Cu-Cr 7 Ni shows a flattening of λ(T ) for T < 2 K down to temperatures as low as T = 20 mK. The main peak of both systems is explained by a Bloembergen-Purcell-Pound (BPP)-like heuristic fitting model that takes into account of a distribution of electronic spin characteristic times for T > 5 K, while the shoulder presented by Cr 7 Ni can be reproduced by a BPP function that incorporates a single electronic characteristic time theoretically predicted to dominate for T < 5 K. The flattening of λ(T ) in Cr 7 Ni-Cu-Cr 7 Ni occurring at very low temperature can be tentatively attributed to field-dependent quantum effects and/or to an inelastic term in the spectral density of the electronic spin fluctuations.

Authors: Sanna, S; Arosio, P; Bordonali, L; Adelnia, F; Mariani, M

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Physical Society
• Journal: Physical Review B
• Volume: 96
• Issue: 18
• Pages: 184403
• Publication date: 2017-11-03
• Acceptance date: 2017-10-26
• DOI: 10.1103/PhysRevB.96.184403
• EISSN: 2469-9969
• ISSN: 2469-9950
• Keywords: Journal Article