A New form of magnetic correlation in Co-doped YbRhSi

Kaneko, Koji   ; Stockert, O.*; Tabata, Chihiro; Kuwahara, Keitaro*; Kiyanagi, Ryoji  ; Nakao, Akiko*; Krellner, C.*; Geibel, C.*

Novel physical phenomena, such as superconductivity and non-Fermi liquid behavior, emerge in the vicinity of a quantum critical point (QCP). YbRhSi has been extensively studied owing to its proximity to an antiferromagnetic (AFM) QCP at ambient pressure. The AFM order at = 70 mK is suppressed by a weak external magnetic field. An inelastic neutron scattering study revealed a competition between ferromagnetic and incommensurate spin fluctuations at q' close to the zone center in YbRhSi, and evolution of resonance-like response at q=0 under magnetic fields. These features suggest an importance of ferromagnetic fluctuations in this system, where as a static AFM order was not confirmed at q'. This fact indicates that the AFM order in YbRhSi may have a different characteristic wave vector. As the latest study discovers emergence of superconductivity at very low temperature, recurring interests on nature of the AFM order burst. A search for an AFM Bragg reflection in YbRhSi has extreme difficulties arising from extremely low , and correspondingly a tiny ordered moment. To overcome these difficulties, we focus on isoelectronic substitution, where substitution of Rh with Co leads to a stabilization of the magnetic order. The huge enhancement of through the Co doping provides us with an opportunity to study the magnetic order closely. Our latest single crystal neutron scattering experiment was carried out on a lower Co concentration of 0.18. A new form of the AFM ordering vector was revealed in the ground state. This provides new insights into magnetic properties of YbRhSi.