Speaker
Description
In the present work, we investigate the spin dynamics of one-dimensional spin-integer molecular nanomagnets ((CH$_3$)$_2$NH$_2$)V$_7$MF$_8$(O$_2$CtBu)$_ {162}$C$_7$H$_8$, with M=Ni/Mn, in short V$_7$M [1,2,3], by means of magnetization, susceptibility and MuSR measurements. These heterometallic nanomagnets contain seven vanadium ions (s=1) and one Ni$^{2+}$ (s=1) or Mn$^{2+}$ (s=5/2) ion, arranged in the form of regular rings. The theoretical studies of rings with a finite number of integer spins indicate a gapped ground state and a significant deviation from the Landé rule, valid for semi-integer spins [4,5]. On the other hand, the infinite spin-integer chain exhibits a topological Haldane gap between the ground state and the first excited state [6]. As confirmed by experimental data, the ground state of V$_7$Ni and V$_7$Mn is expected to be antiferromagnetic, similarly to the molecular nanomagnet V$_7$Zn [1,2,7], and the exchange coupling constants among the nearest neighbour magnetic ions are estimated to be of the order of a few Kelvin degrees. Susceptibility and magnetization measurements at low temperatures display anisotropy effects when an external magnetic field is applied. The muon longitudinal relaxation rate $\lambda$ vs temperature, at magnetic fields $\mu_0 H \geq$ 500 G, in the range $1.5\leq T\leq 100 K$, follows a heuristic Bloembergen-Purcell-Pound model [8]. No effect related to a topological gap is evinced.
References
[1] F. Adelnia, PhD thesis in Physics, Università degli studi di Pavia (2016).
[2] F. Adelnia et al., Applied Magnetic Resonance 51, 1277 (2020).
[3] I. Villa, BD thesis in Physics, Università degli studi di Milano (2018).
[4] J. Schnack et al., Phys. Rev. B 63, 014418 (2020).
[5] D. Gatteschi et al., Oxford University Press (2011).
[6] F. Haldane, Phys. Letters A 93, 464 (1983).
[7] F. A. Rusnati, MD thesis in Physics, Università degli studi di Milano (2017).
[8] N. Bloembergen et al., Phys. Rev. 73, 679 (1948).
