Evidence for a ferromagnetic quantum critical point in URhGe doped with Ru

Abstract

We have investigated the evolution of ferromagnetic order in the correlated metal series URh 1-x Ru x Ge. Magnetization, transport and specific heat measurements provide convincing evidence for a ferromagnetic quantum critical point at the critical concentration x c = 0.38. Here we report ac-susceptibility and magnetization measurements on selected samples with Ru doping concentrations near the critical point.Keywords: URhGe; ferromagnetism; chemical substitution; quantum phase transition The intermetallic compound URhGe attracts much attention because itinerant ferromagnetism (T C = 9.5 K) and unconventional superconductivity (T s = 0.25 K) coexist [1]. Moreover, re-entrant superconductivity is observed for a magnetic field B ≈ 12 T applied along the orthorhombic b-axis [1]. A natural explanation for the occurrence of these unusual superconducting states is that critical magnetic fluctuations stimulate the formation of spintriplet Cooper pairs. Therefore it is of considerable interest to explore the magnetic properties of URhGe, especially as far as the ferromagnetic (FM) instability is concerned.Recently, we have investigated the evolution of FM order in URhGe doped with Ru, Co and Si [2]. Magnetization and transport experiments on a series of polycrystalline URh 1-x Ru x Ge samples down to T = 2 K showed that FM order, after an initial weak increase, is suppressed in a linear fashion and disappears at a critical concentration x c = 0.38 (see Fig.1). In fact these experiments hinted at the existence of a FM quantum critical point (QCP) in the U(Rh,Ru)Ge system. This was corroborated by subsequent low temperature (T ≥ 0.3 K) specific-heat and resistivity measurements [3]. At x c the phononcorrected specific heat varies as c ~ Tln(T/T 0 ) over a wide T range and γ(x) (i.e. (c/T)| 0.5K ) goes through a pronounced maximum. The critical behaviour is also tracked by the exponent of the resistivity ρ ~ T n , which attains a minimum value n = 1.2 at x c . Taking into account that the magnetization data show a smooth suppression of the ordered moment m 0 (x), these results provide convincing evidence for a continuous FM quantum phase transition in the U(Rh,Ru)Ge system [3].In this work we further investigate the phase diagram in the vicinity of the critical point. We report low temperature (T ≥ 0.23 K) ac-susceptibility, χ ac , measurements in a field of 10 -5 T. The data were taken on arc-melted polycrystalline samples annealed at 875 o C for 10 days. In Fig.2 we show the results for x = 0.35 and 0.375. The maxima in χ ac signal FM

Switching of magnetic ground states across the UIr1−xRhxGe alloy system

“…Existence of quantum critical points (QCPs) were reported in the neighboring alloying FM-PM and AFM-paramagnetic (PM) systems URh 1-x Ru x Ge 29,44 , UCo 1-x Fe x Ge 28 , UCo 1-x Ru x Ge 4 or UPd 1-x Ru x Ge 21 . The UIr 1-x Rh x Ge system behaves like the other AFM/FM alloy system UPd 1x Co x Ge where magnetic order survives in the entire concentration range 22 .…”

Electronic structure of ferromagnetic heavy fermion, YbPdSi, YbPdGe, and YbPtGe studied by photoelectron spectroscopy, x-ray emission spectroscopy, and DFT + DMFT calculations

“…The fits to the valence band spectra show that the Yb valence of YbPtGe is slightly smaller than those of YbPdSi and YbPdGe 14 . This explains that the magnitude of the ordered magnetic moment of YbPtGe is smaller than the other two compounds due to screening by the Kondo effect.…”

“…The Ce compounds CeRu 1−xFexPO [8] and CeIrB 2 [9] display a ferromagnetic Kondo lattice and a ferromagnetic QCP, respectively. The ferromagnetic order coexists with superconductivity around the QCP in the uranium compounds UGe 2 [10], URhGe [11,12], and UCoGe [13,14], although in these cases the Kondo-lattice formation is unclear.…”