Muon spin rotation and neutron scattering study of the noncentrosymmetric tetragonal compoundCeAuAl3

Abstract

We have investigated the noncentrosymmetric tetragonal heavy fermion compound CeAuAl 3 using muon spin rotation (μSR), neutron diffraction (ND), and inelastic neutron scattering (INS) measurements. We have also revisited the magnetic, transport, and thermal properties. The magnetic susceptibility reveals an antiferromagnetic transition at 1.1 K with, possibly, another magnetic transition near 0.18 K. The heat capacity shows a sharp λ-type anomaly at 1.1 K in zero field, which broadens and moves to a higher temperature in an applied magnetic field. Our zero-field μSR and ND measurements confirm the existence of a long-range magnetic ground state below 1.2 K. Further, the ND study reveals an incommensurate magnetic order with a magnetic propagation vector k = (0,0,0.52(1)) and a spiral structure of Ce moments coupled ferromagnetically within the ab plane. Our INS study reveals the presence of two well-defined crystal electric field (CEF) excitations at 5.1 and 24.6 meV in the paramagnetic phase of CeAuAl 3 that can be explained on the basis of the CEF theory and the Kramer's theorem for a Ce ion having a 4f 1 electronic state. Furthermore, low energy quasielastic excitations show a Gaussian line shape below 30 K compared to a Lorentzian line shape above 30 K, indicating a slowdown of spin fluctuations below 30 K. We have estimated a Kondo temperature of T K = 3.5 K from the quasielastic linewidth, which is in good agreement with that estimated from the heat capacity. This study also indicates the absence of any CEF-phonon coupling unlike that observed in isostructural CeCuAl 3 The CEF parameters, energy level scheme, and their wave functions obtained from the analysis of INS data explain satisfactorily the single crystal susceptibility in the presence of two-ion anisotropic exchange interaction in CeAuAl 3 .

Magnetoelastic hybrid excitations in CeAuAl 3

“…2 B ). The energy of this transition is in excellent agreement with previous time-of-flight neutron spectroscopy and bulk data in a polycrystalline sample, which, however, did not allow a search for a momentum dependence (50, 54). The weak nondispersive excitation at EnormalVnormalBnormalS=7.9 normalmnormalenormalV (Fig.…”

“…1 A ), a member of the normalCnormalenormalTnormalAnormall3 series (T = Ce, Au, Pd, Pt) and thus the wider family of normalBnormalanormalAnormall4-type materials (52). Early measurements of the bulk and transport properties of polycrystalline samples established normalCnormalenormalAnormalunormalAnormall3 as a Kondo lattice compound stabilizing incommensurate antiferromagnetic order below TnormalN=1.32 K (50, 54). The enhancement of the linear temperature dependence of the specific heat and quadratic temperature dependence of the resistivity (γ=227 mJ⋅mol−1⋅normalK−2 and A=5 normalμnormalΩnormalcnormalm⋅normalK−2, respectively) are characteristic of a heavy Fermi liquid state.…”

“…This suggests that the symmetry of the lattice fluctuations imparts a different character on the VBS in tetragonal compared with cubic systems. However, systematic time-of-flight neutron spectroscopy in polycrystalline normalCnormalenormalRnormalhnormalGnormale3 (58) and normalCnormalenormalAnormalunormalAnormall3 (54) failed to detect a VBS. Moreover, the search for ME phonon softening by inelastic X-ray scattering in normalCnormalenormalCnormalunormalAnormall3 and normalCnormalenormalAnormalunormalAnormall3 has been inconclusive (59).…”

Single crystal growth of CeTAl3 (T = Cu, Ag, Au, Pd and Pt)

“…In CeCuAl 3 it has been reported that they are low lying with ∆ 1 =15 K and ∆ 2 = 238 K [8,25]. Further for CeAuAl 3 excited levels of ∆ 1 =57 K and ∆ 2 = 265 K [32] Magnetic ground states in CeTX 3 compounds are usually antiferromagnetic, as in CeCuAl 3 with T N = 2.1 K and CeAuAl 3 with T N = 1.32 K. However, the exact magnetic ground states are more complicated, with a propagation vector k = (0.4, 0.6, 0) in the case of CeCuAl 3 [20] and k = (0, 0, 0.52) for CeAuAl 3 [1]. CeAgAl 3 is a rare example of ferromagnetic Ce-compound below the ordering temperature of T = 3.2 K. CePdAl 3 is reported to order antiferromagnetically below 6 K, CePtAl 3 exhibits spin-glass behaviour below 0.8 K.…”

“…Under pressure, T N rises up to 60 kbar in CeCuAl 3 and suddenly vanishes at 80 kbar [18,30], pointing towards the existence of a quantum critical point (QCP). Recently, a phonon -crystal field quasibound state has been found in CeCuAl 3 [2], which is not present in CeAuAl 3 [1]. Furthermore, a low energy anomalous excitation [4] and phonon scattering by Ce magnetic moment fluctuations are reported in CeAuAl 3 [5], as well as a possible second phase transition at 0.18 K [1].…”