Contiguous 3d and 4f magnetism: towards strongly correlated 3d electrons in YbFe2Al10

We present magnetization, specific heat, and 27Al NMR investigations on YbFe2Al10 over a wide range in temperature and magnetic field. The magnetic susceptibility at low temperatures is strongly enhanced at weak magnetic fields, accompanied by a ln(T0/T) divergence of the low-T specific heat coefficient in zero field, which indicates a ground state of correlated electrons. From our hard X-ray photo emission spectroscopy (HAXPES) study, the Yb valence at 50 K is evaluated to be 2.38. The system displays valence fluctuating behavior in the low to intermediate temperature range, whereas above 400 K, Yb3+ carries a full and stable moment, and Fe carries a moment of about 3.1 mB. The enhanced value of the Sommerfeld Wilson ratio and the dynamic scaling of spin-lattice relaxation rate divided by T [27(1/T1T)] with static susceptibility suggests admixed ferromagnetic correlations. 27(1/T1T) simultaneously tracks the valence fluctuations from the 4f -Yb ions in the high temperature range and field dependent antiferromagnetic correlations among partially Kondo screened Fe 3d moments at low temperature, the latter evolve out of an Yb 4f admixed conduction band.Comment: To appear in Phys. Rev. Let

Evidence for strong f -d hybridization in intermetallic ferromagnet CePdIn2

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Electronic, magnetic, and transport properties of the isotypic aluminides SmT₂Al₁₀ (T = Fe, Ru)

We report the results of a comprehensive physical and magnetic property study of the new isotypic aluminides SmT2Al10 (T = Fe, Ru). These two compounds are members of a rare-earth based system which has become an exemplary case study of the interplay of magnetism and correlated electron phenomena. SmFe2Al10 and SmRu2Al10 are found to order in a putative antiferromagnetic spin arrangement at T-N = 14.5 K and 12.5 K, respectively. Moreover, SmRu2Al10 shows a further phase transition at T-SR = 5 K which is likely due to spin reorientation. The susceptibility of SmFe2Al10 points to a valence instability of the Sm ionic state at intermediate temperatures well above T-N. Electronic and thermal transport confirm that SmFe2Al10 undergoes an antiferromagnetic superzone gap formation below T-N, whereas SmRu2Al10 suffers a lattice anomaly driven magnetoelastic coupling at T-N. Below T-N, the physical properties of SmT2Al10 (T = Fe, Ru) are governed by magnons with an antiferromagnetic spin-wave spectrum that reveals spin-gap opening. Our findings in this work have exposed a new anomalous correlated compound in the RT2Al10 series. SmFe2Al10 has a magnetic ordered ground state in spite of an unstable valence at higher temperature. This is comparable with CeRu2Al10, which is a unique and controversial Kondo insulator that orders antiferromagnetic at T-N = 27 K. Among the series of rare-earth RT2Al10 compounds, the presented Sm compounds are two new members with anomalously high magnetic ordering temperatures, and it is envisaged that together with the two very well studied compounds CeRu2Al10 and CeOs2Al10 our presented studies will enable a broader approach towards understanding the fascinating properties of this materials class

Effects of Y- and La-doping on the magnetic ordering, Kondo effect, and spin dynamics in Ce_1-xM_xRu₂Al₁₀

The influence of Y- and La-substitution for Ce on the competing Kondo effect and magnetic ordering, as well as on spin dynamics in the Kondo semiconductor CeRu2Al10 have been investigated by means of thermal, electronic, and magnetic properties. The parent compound CeRu2Al10 is known to be a controversial antiferromagnet with high magnetic ordering temperature T (0) = 27 K. A small negative chemical pressure caused by La-doping results rapid suppression of T (0) and spin gap energy Delta( m ), compared to a small positive pressure caused by Y-doping. Upon Y- and La-doping, the electrical resistivity rho(T) illustrates the evolution from dense Kondo semiconductor to incoherent single-ion Kondo behaviour, and hence weakens the c-f hybridization and thus lowers the Kondo temperature. The 5% Y- and La-doped compounds show enormous enhancement in the thermoelectric power and complex behaviour in the Hall resistivity below T (0) due to an abrupt change in charge carrier mobility with temperature. The magnetic contribution to electrical resistivity rho (mag)(T) (greater than or similar to 50% La) and specific heat C (P)(T)/T (greater than or similar to 70% La) evidence non-Fermi-liquid behaviour at low temperature in the La-doped system, due to interplay of atomic disorder with spin-fluctuation. Application of magnetic field suppresses the spin-fluctuation in C (P)(T)/T and eventually emerges to Fermi-liquid state in the 95% La-doped compound in 9 T. The magnetic phase diagram illustrates that the strength of the Kondo interaction in the doped systems are primarily controlled by the effect of volume change as described by the compressible Kondo lattice model. We ascribe the fascinating observation of T (K) similar or equal to 4T (0) to anisotropy in the single-ion crystal electric field in the presence of strong anisotropic c-f hybridization

Long-range magnetic order in CeRu2Al10 studied via muon spin relaxation and neutron diffraction

The low temperature state of CeRu2Al10 has been studied by neutron powder diffraction and muon spin relaxation (muSR). By combining both techniques, we prove that the transition occurring below T*~27K, which has been the subject of considerable debate, is unambiguously magnetic due to the ordering of the Ce sublattice. The magnetic structure with propagation vector k=(1,0,0) involves collinear antiferromagnetic alignment of the Ce moments along the c-axis of the Cmcm space group with a reduced moment of 0.34(2)mu_B. No structural changes within the resolution limit have been detected below the transition temperature. However, the temperature dependence of the magnetic Bragg peaks and the muon precession frequency show an anomaly around T2~12 K indicating a possible second transition