Domain wall dynamics in a near-Ising ferromagnetic chain CoCl2*2D2O

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• Ursula Bengaard Hansen, Institut Laue-Langevin (ILL), Grenoble, France.
• Friday 23 April 2021, 14:00-15:00
• https://bham-ac-uk.zoom.us/j/83190378684?pwd=ZzRIK1VFMGZCc0FCT3dkQnN4QStCZz09.

If you have a question about this talk, please contact Mingee Chung.

In this presentation, I will discuss the magnetic excitations of a near-Ising ferromagnet in a longitudinal field. The near Ising ferromagnetic chain has a characteristic excitation spectrum. In zero field, the elementary excitations are clusters of overturned spins, in a pure Ising system the excitation energy of these clusters are degenerate and hence independent of the number of flipped spins, the cost of creating a spin cluster comes only from the domain walls at either end of the cluster. This degeneracy can be lifted by inter-chain interactions, non Ising terms in the Hamiltonian or magnetic fields. It has been proposed, that the dynamics of the domain walls of the cluster excitations in the presence of a longitudinal magnetic field, can be interpreted as a magnetic analogue of electronic Bloch Oscillations [1], which is the phenomena where a charged particle in a periodic lattice starts to oscillate when a constant electric field is applied. It has been predicted [2] that the signatures of these Magnetic Bloch Oscillations may be observed using inelastic neutron scattering.

We have studied the dynamic behaviour of the cluster excitations in CoCl2.2D2O at the MACS neutron spectrometer [3]. Here I will present our results and how we are able to account for the different features in the excitation spectrums using a Random-Phase Approximation [4], that also accounts for the non one-dimensional magnetic interactions that are nevertheless still present in CoCl2.2D2O.

[1] F. Bloch, Zeitschrift für Physik 52, 555 (1929) [2] S. Shinkevich and O. Syljuåsen, PRB 85 , 104408 (2012) [3] U. B. Hansen, arXiv preprint arXiv:1906.11554, 2019 [4] J. Jensen, PRB , 97(2), 024423 (2018)

This talk is part of the Condensed Matter Physics Seminars series.

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