TY - JOUR
T1 - High-field magnetic phase transitions and spin excitations in magnetoelectric LiNiPO4
AU - Toft-Petersen, Rasmus
AU - Jensen, Jens
AU - Jensen, Thomas Bagger Stibius
AU - Andersen, Niels Hessel
AU - Christensen, Niels Bech
AU - Niedermayer, Christof
AU - Kenzelmann, Michel
AU - Skoulatos, Markos
AU - Le, MD
AU - Lefmann, Kim
AU - Hansen, Sonja Rosenlund
AU - Li, Jiying
AU - Zarestky, Jerel L.
AU - Vaknin, David
PY - 2011
Y1 - 2011
N2 - The magnetically ordered phases and spin dynamics of magnetoelectric LiNiPO4 have been studied in fields up to 17.3 T along the c axis. Using neutron diffraction, we show that a previously proposed linearly polarized incommensurate (IC) structure exists only for temperatures just below the Neel temperature T-N. The ordered IC structure at the lowest temperatures is shown instead to be an elliptically polarized canted spiral for fields larger than 12 T. The transition between the two IC phases is of second order and takes place about 2 K below T-N. For mu H-0 > 16 T and temperatures below 10 K, the spiral structure is found to lock in to a period of five crystallographic unit cells along the b axis. Based on the neutron-diffraction data, combined with detailed magnetization measurements along all three crystallographic axes, we establish the magnetic phase diagrams for fields up to 17.3 T along c and for fields up to 16 T along a and b. The spin excitations in the high-field IC spiral phase have been studied in detail by inelastic neutron scattering. A mean-field analysis shows that the spin Hamiltonian derived previously from the low-temperature spin waves at zero field predicts the transition between the linear and elliptical polarization of the IC structure, and that a generalization of the spin-wave theory, assuming the random-phase approximation, accounts for the inelastic scattering data obtained in the commensurable uniform phase at fields below 12 T as well as those obtained in the high-field IC spiral phase.
AB - The magnetically ordered phases and spin dynamics of magnetoelectric LiNiPO4 have been studied in fields up to 17.3 T along the c axis. Using neutron diffraction, we show that a previously proposed linearly polarized incommensurate (IC) structure exists only for temperatures just below the Neel temperature T-N. The ordered IC structure at the lowest temperatures is shown instead to be an elliptically polarized canted spiral for fields larger than 12 T. The transition between the two IC phases is of second order and takes place about 2 K below T-N. For mu H-0 > 16 T and temperatures below 10 K, the spiral structure is found to lock in to a period of five crystallographic unit cells along the b axis. Based on the neutron-diffraction data, combined with detailed magnetization measurements along all three crystallographic axes, we establish the magnetic phase diagrams for fields up to 17.3 T along c and for fields up to 16 T along a and b. The spin excitations in the high-field IC spiral phase have been studied in detail by inelastic neutron scattering. A mean-field analysis shows that the spin Hamiltonian derived previously from the low-temperature spin waves at zero field predicts the transition between the linear and elliptical polarization of the IC structure, and that a generalization of the spin-wave theory, assuming the random-phase approximation, accounts for the inelastic scattering data obtained in the commensurable uniform phase at fields below 12 T as well as those obtained in the high-field IC spiral phase.
KW - Superconducting materials
KW - Superledende materialer
U2 - 10.1103/PhysRevB.84.054408
DO - 10.1103/PhysRevB.84.054408
M3 - Journal article
SN - 0163-1829
VL - 84
SP - 054408 (10 pages)
JO - Physical Review B Condensed Matter
JF - Physical Review B Condensed Matter
IS - 5
ER -