Tweaking the spin-wave dispersion and suppressing the incommensurate phase in LiNiPO${}_4$ by iron substitution

Abstract

Elastic and inelastic neutron scattering studies of Li(Ni${}_{1-x}$Fe${}_x$)PO${}_4$ single crystals reveal anomalous spin-wave dispersions along the crystallographic direction parallel to the characteristic wave vector of the magnetic incommensurate phase. The anomalous spin-wave dispersion ({\it magnetic soft mode}) indicates the instability of the Ising-like ground state that eventually evolves into the incommensurate phase as the temperature is raised. The pure LiNiPO${}_4$ system ($x=0$), undergoes a first-order magnetic phase transition from a long-range incommensurate phase to an antiferromagnetic ground state at {\it T}${}_N$ = 20.8 K. At 20% Fe concentrations, although the AFM ground state is to a large extent preserved as that of the pure system, the phase transition is second-order, and the incommensurate phase is completely suppressed. Analysis of the dispersion curves using a Heisenberg spin Hamiltonian that includes inter- and in-plane nearest and next-nearest neighbor couplings reveals frustration due to strong competing interactions between nearest- and a next-nearest neighbor site, consistent with the observed incommensurate structure. The Fe substitution only slightly lowers the extent of the frustration, sufficient to suppress the IC phase. An energy gap in the dispersion curves gradually decreases with the increase of Fe content from $\sim$2 meV for the pure system ($x=0$) to $\sim$0.9 meV for $x=0.2$.

References in corpus (8)

• Statics and dynamics of an incommensurate spin order in a geometrically frustrated antiferromagnet CdCr${}_2$O${}_4$
• Formation of a magnetic soliton lattice in copper metaborate
• Commensurate-Incommensurate Magnetic Phase Transition in Magnetoelectric Single Crystal LiNiPO${}_4$
• Spin-waves in antiferromagnetic single crystal LiFePO${}_4$
• Field-induced magnetic phases and electric polarization in LiNiPO4
• Spin Dynamics in the Magnetoelectric Effect LiCoPO${}_4$ Compound
• Antiferromagnetism in the magnetoelectric effect single crystal LiMnPO${}_4$
• Anomalous spin-waves and the commensurate-incommensurate magnetic phase transition in LiNiPO4

Cited by in corpus (5)

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• Spin excitations of magnetoelectric LiNiPO${}_4$ in multiple magnetic phases
• Tuning magnetoelectricity in a mixed-anisotropy antiferromagnet
• Growth, characterization, and magnetic properties of a Li(Mn,Ni)PO4 single crystal
• Exceptional field dependence of antiferromagnetic magnons in LiFePO${}_4$