Neutron Scattering Studies of Spin Waves and Magnetic Transitions
in Magnetoelectric Materials Li(Ni1-xFex)PO4 (x = 0 and 0.2)
Jiying Li,
Iowa State University
Recently, considerable research attention has been focused on the
multiferroics (materials with coexisting of magnetic and electric
ordering). Lithium orthophosphates with a general formula of
LiMPO4 (M = Mn, Fe, Co, and Ni) are another group of compounds
where the magnetic and electrical ordering interact. Elastic
neutron scattering studies show that LiNiPO4 undergoes a first-order
magnetic phase transition from a long-range incommensurate phase to a
collinear antiferromagnetic ground state at TN = 20.8 K. Gradual Fe
substitution for Ni demonstrates the properties of the pure system (x=0)
are practically preserved up to a ~ 20% Fe content (x=0.8). At this Fe
concentration, although the AF ground state is the same as that of the pure
system, the phase transition in LiNi0.8Fe0.2PO4
changes from first- to
second-order, and the incommensurate phase is inhibited. Inelastic
neutron scattering studies reveal anomalous spin-wave dispersion curves
(magnetic soft mode) along the incommensurate phase direction in LiNiPO4.
Fe substitution for Ni eliminates the magnetic soft mode in the dispersion curve.
Analysis of the dispersion curves using a Heisenberg spin Hamiltonian,
that includes inter and intra-plane nearest and next-nearest neighbor
couplings, reveals strong frustration of a next-nearest neighbor site
consistent with the observed IC structure. The Fe substitution just slightly
lowers the extent of the frustration, however it is sufficient in eliminating
the IC phase, giving rise to strong diffuse scattering instead.
Back to Seminar Home Page
Last modified 30-October-2006 by website owner: NCNR (attn: )
