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Register a new userField-induced magnetic phases and electric polarization in LiNiPO4
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Thomas Bagger Stibius Jensen
Publication date
2009
fields
Physics
and research's language is
English
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Neutron diffraction is used to probe the (H,T) phase diagram of magneto-electric (ME) LiNiPO4 for magnetic fields along the c-axis. At zero field the Ni spins order in two antiferromagnetic phases. One has commensurate (C) structures and general ordering vectors (0,0,0), the other one is incommensurate (IC) with ordering vector (0,q,0). At low temperatures the C order collapses above 12 Tesla and adopts an IC structure with modulation vector parallel to (0,q,0). We show that C order is required for the ME effect and establish how electric polarization results from a field-induced reduction of the total magneto-elastic energy.
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Detailed spin-wave spectra of magneto-electric LiNiPO4 have been measured by neutron scattering at low temperatures in the commensurate (C) antiferromagnetic (AF) phase with ordering temperature 20.8 K. An anomalous low-energy mode is observed at the modulation vector of the incommensurate (IC) AF phase appearing above the 20.8 K. A linear spin-wave model based on Heisenberg exchange couplings and single ion anisotropies accounts for all the observed spin-wave dispersions and intensities. Along the b axis an unusually strong next-nearest-neighbor AF coupling competes with the dominant nearest-neighbor AF exchange interaction and causes the IC structure.
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