Investigation of the magnetic dipole field at the atomic scale in quasi-one-dimensional paramagnetic conductor Li₀.₉Mo₆O₁₇

الأصل · EN

We report magnetic dipole field investigation at the atomic scale in a single crystal of quasi-one-dimensional (Q1D) paramagnetic conductor Li₀.₉Mo₆O₁₇, using a paramagnetic electron model and ⁷Li-NMR spectroscopy measurements with an externally applied magnetic field B₀ = 9 T. We find that the magnetic dipole field component (B||dip) parallel to B₀ at the Li site from the Mo electrons has no lattice axial symmetry; it is small around the middle between the lattice c and a axes in the ac-plane with the minimum at the field orientation angle θ = +52.5∘, while the B||dip maximum is at θ = +142.5∘ when B₀ is applied perpendicular to b (B₀ ⊥ b), where θ = 0∘ represents the direction of B₀ ∥ c. Further estimate indicates that B||dip has a maximum value of 0.35 G at B₀ = 9 T, and the Mo ions have a possible effective magnetic dipole moment 0.015 μB per ion, which is significantly smaller than that of a spin 1/2 free electron. By minimizing potential magnetic contributions to the NMR spectrum satellites with the NMR spectroscopy measurements at the direction where the value of the magnetic dipole field is the smallest, the behavior of the independent charge contributions is observed. This work demonstrates that the magnetic dipole field from the Mo electrons is the dominant source of the local magnetic fields at the Li site, and it suggests that the mysterious "metal-insulator" crossover at low temperatures is not a charge effect. The work also reveals valuable local field information for further NMR investigation which is suggested recently [Phys. Rev. B 85, 235128 (2012)] to be key important to the understanding of many mysterious properties of this Q1D material of particular interest.