Spin waves near the edge of halogen substitution induced magnetic order in Ni(Cl1−xBrx)2·4

Abstract

We report an inelastic neutron scattering study of magnetic excitations in a quantum paramagnet driven into a magnetically ordered state by chemical substitution, namely Ni(Cl1−xBrx)2·4SC(NH2)2 with x = 0.21(2). The measured spectrum is well accounted for by the generalized spin wave theory (GSWT) approach [M. Matsumoto and M. Koga, J. Phys. Soc. Jap. 76, 073709 (2007)]. This analysis allows us to determine the effective Hamiltonian parameters for a direct comparison with those in the previously studied parent compound and "underdoped" system. The issue of magnon lifetimes due to structural disorder is also addressed. * povarovk@phys.ethz.ch †

Microwave dynamics of the stoichiometric and bond-disordered anisotropic S=1 chain antiferromagnet NiCl2−4SC(NH2Soldatov1, Смирнов2, Povarov3 et al. 2020Phys. Rev. BSelf Cite5190View full textAdd to dashboardCite

“…[15]and a gap of 1.06 ± 0.04 meV (256 ± 10 GHz) measured in neutron experiments with pure samples [9]. The value of ∆ 1 for x = 0.21, measured in neutron scattering experiments 1.1 meV [13,14] is almost the same. We observe that branches A and B in the paramagnetic phase (at T = 1.4 K) cross at a frequency of 10 GHz.…”

“…Thereby the two-branch antiferromagnetic resonance spectrum with a gapped mode and a true Goldstone mode is experimentally confirmed. The upper gap of the antiferromagnetic resonance was found to be reduced in the Br-doped sample with x = 0.21, despite the rise of the exchange integral near Br-impurity [16] and the widening of the magnon band [14].…”

“…Single-crystalline samples of DTN and DTNX used in our experiments are from the same batches as studied in previous ESR and neutron scattering experiments [12][13][14][15]18]. Experimental results presented in Figs.…”

“…Br-ions substitute Clions and this creates bond disorder via local variations of exchange and anisotropy parameters. Zero-field neutron scattering experiments [11][12][13][14] reveal a decrease of the spin excitation gap at the boundary of the Brillouin zone for Ni(Cl 1−x Br x ) 2 -4SC(NH 2 ) 2 (DTNX). This gap is completely closed at x ≃ 0.16 [12][13][14].…”

“…Zero-field neutron scattering experiments [11][12][13][14] reveal a decrease of the spin excitation gap at the boundary of the Brillouin zone for Ni(Cl 1−x Br x ) 2 -4SC(NH 2 ) 2 (DTNX). This gap is completely closed at x ≃ 0.16 [12][13][14]. At x = 0.21 the antiferromagnetic long range order appears even at zero field at T N = 0.64 K [13].…”