Abstract
Spin spirals, which coexist with collinear spin order in linarite PbCuSO4(OH)2, indicate electrical polarisation textures of spin-multipolar phases. We derive experimental evidence by a detailed investigation of the magnetic-field dependent dielectric and electric polarization properties at low temperatures. Linarite exhibits a quasi-one-dimensional frustrated S = ½ spin chain, which forms 3D spin-spiral order in zero magnetic field for T < 2.85 K. Recently, due to the monoclinic lattice of linarite with CuO2 ribbon chains, complex magnetic field induced states were found. These spin-multipolar phases, which compete with spin-density waves at low magnetic fields, exist in close vicinity to the transition from the spin spiral into field induced spin polarized state. Via antisymmetric Dzyaloshinskii-Moriya interaction spin-driven ferroelectricity develops in the spin-spirals state. Via electric polarization measurements this allows to prove the transitions into complex magnetic field induced phases. Thorough analyses of the temperature and magnetic field dependent dielectric properties of a naturally grown single crystalline sample provide a detailed (T,H) phase diagrams for the three different crystallographic directions.
Highlights
We investigated in detail the multiferroic properties of natural grown single crystalline linarite
This material exhibits a rich variety of complex multiferroic phases for T < TN
Via magnetic field dependent dielectric and polarization experiments we found clear evidence that the improper ferroelectric transitions follow the P ∝ e × Q relation
Summary
In analogy to LiCuVO413, Fig. 2 schematically shows the ground state of the spiral spin configuration as function of magnetic field. In addition the peak height of Δε’ and the magnitude of the polarization decrease by a factor of two by increasing the magnetic field up to 4 T This reduced polarisation originates from the rotation of the spiral spin axis from [1 0 1] into a-direction. Field-dependent dielectric measurements reveal no significant transitions of the SMP into a field induced spin-polarized state It seems, that only Δε’(T) for H > H1 is sensitive to a polar order resulting from instabilities of various spin spirals within the SMP. That only Δε’(T) for H > H1 is sensitive to a polar order resulting from instabilities of various spin spirals within the SMP This further indicates that the observed polarization is a function of magnetic and thermal treatment and only detectable by dielectric measurements, when starting in the paramagnetic disordered state above TN.
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