High-field magnetic phase transitions and spin excitations in magnetoelectric LiNiPO4

TY - JOUR

T1 - High-field magnetic phase transitions and spin excitations in magnetoelectric LiNiPO4

AU - Toft-Petersen, R.

AU - Jensen, Jens

AU - Jensen, T. B. S.

AU - Andersen, N. H.

AU - Christensen, N. B.

AU - Niedermayer, C.

AU - Kenzelmann, M.

AU - Skoulatos, M.

AU - Le, M.D.

AU - Lefmann, Kim

AU - Hansen, S. R.

AU - Li, J.

AU - Zarestky, J. L.

AU - Vaknin, D.

PY - 2011/8/2

Y1 - 2011/8/2

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 Néel temperature TN. 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 TN. For μ0H16 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 Néel temperature TN. 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 TN. For μ0H16 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.

U2 - 10.1103/PhysRevB.84.054408

DO - 10.1103/PhysRevB.84.054408

M3 - Journal article

SN - 2469-9950

VL - 84

SP - 054408

JO - Physical Review B

JF - Physical Review B

IS - 5

ER -