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Description
We report high-frequency ESR studies on a powder sample of the frustrated quasi-1D spin-1/2 chain material PbCuSeO$_4$(OH)$_2$, isostructural to the well studied natural mineral linarite (PbCuSO$_4$(OH)$_2$). Magnetisation data show the evolution of a magnetically ordered phase below $T_{\rm N}$ = 4.3~K and a spin-flop transition at $B_{\rm SF}$ = 2.8~T.
ESR measurements on a loose powder evidence a gapless linear excitation mode within the ground state, which can be traced across the spin-flop transition, as well as two linear excitation modes within the in-field phase with a zero field gap of $-31\pm9$~GHz and $32.9\pm1.4$~GHz. Measurements on a fixed powder reveal a gapped magnon mode in the ground state with a zero field splitting of $70\pm20$~GHz. This mode may be accounted for by assuming an excitation of a spiral spin order in the ground state.
Tracing the resonance positions with temperature suggests an easy-axis type anisotropy with the paramagnetic g-factors 2.3 and 2.07. Changes in resonance position evidence the onset of short range fluctuations at 70~K and the evolution of orthorombic anisotropy.
| Category | Solid State (Experiment) |
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