Workshop "NMR, µSR, Mössbauer spectroscopies in the study of Fe-based and other unconventional high-Tc superconductors"
Local susceptibility and spin dynamics of ferromagnetic quantum critical system YbNi4(P1-xAsx)2: NMR and µSR investigation
Rajib Sarkar, TU Dresden, Germany
In the last 10 years there was growing evidence both from theoretical work and experimental observations that a ferromagnetic (FM) quantum critical point (QCP) cannot exist in a pure system, because the transition becomes first order before reaching the QCP. Therefore the recent report of clear evidence for a FM-QCP in the heavy fermion compounds YbNi4(P1-xAsx)2 attracted considerable attention . While the Bravais lattice of this compound is tetragonal, resulting in isotropic in-plane macroscopic magnetic properties, the local symmetry on the Yb site (and on the P-site) is lower, orthorhombic. Therefore some in-plane anisotropy of local magnetic properties is expected, which could however not yet been studied because of the absence of related effects on macroscopic properties. We performed 31P NMR investigations on a grain aligned polycrystalline sample of YbNi4P2. We observed three structures in the NMR spectra, which present quite different T dependence of the respective Knight shifts. An analysis of these results provides a clear evidence for strong local in-plane anisotropy of the Yb moment due to the orthorhombic crystal electric field. Implication for the magnetic ordered state shall be discussed. In addition to that μSR results for x ≤ 0.13 and the dynamics of the quantum fluctuations at the ferromagnetic quantum critical point shall be discussed.