The Kondo semiconductor CeOs 2 Al 10 exhibits an antiferromagnetic (AFM) order at T N = 28.5 K, whose temperature is unexpectedly high for the small ordered moment of 0.3 µ B /Ce. We have studied the effects of electron-and hole-doping on the hybridization gap and AFM order by measuring the magnetization M , magnetic susceptibility χ, electrical resistivity ρ, and specific heat C on single crystals of Ce(Os 1−x Ir x ) 2 Al 10 (x ≤ 0.15) and Ce(Os 1−y Re y ) 2 Al 10 (y ≤ 0.1). The results of M (B) indicates that the AFM ordered moment µ AF changes the direction from the caxis for x = 0 to the a-axis for x = 0.03. With increasing x up to 0.15, T N gradually decreases although the 4f electron state becomes localized and the magnitude of µ AF is increased to 1 µ B /Ce.With increasing y, the 4f electron state is more delocalized and the AFM order disappears at a small doping level y = 0.05. In both electron-and hole-doped systems, the suppression of T N is well correlated with the increase of the Sommerfeld coefficient γ in C(T ). Furthermore, the simultaneous suppression of T N and the semiconducting gap in ρ(T ) at T > T N indicates that the presence of the hybridization gap is indispensable for the unusual AFM order in CeOs 2 Al 10 .

The effect of Ir substitution for Os in CeOs2Al10, with an unusually high Neel temperature of T * ∼28.5K, has been studied by high-resolution neutron diffraction and magnetization measurements. A small amount of Ir (∼ 8%) results in a pronounced change of the magnetic structure of the Ce-sublattice. The new magnetic ground state is controlled by the single ion anisotropy and implies antiferromagnetic arrangement of the Ce-moments along the a-axis, as expected from the anisotropy of the paramagnetic susceptibility. The value of the ordered moments, 0.92(1) µB, is substantially bigger than in the undoped compound, whereas the transition temperature is reduced down to 21K. A comparison of the observed phenomena with the recently studied CeRu1.9Rh0.1Al10 system, exhibiting similar behaviour [A. Kondo et al., J. Phys. Soc. Jpn. 82, 054709 (2013)], strongly suggests the electron doping as the main origin of the ground state changes. This provides a new way of exploring the anomalous magnetic properties of the Ce(Ru/Os)2Al10 compounds.

The opening of a spin gap in the orthorhombic compounds CeT2Al10 (T = Ru and Os) is followed by antiferromagnetic ordering at TN = 27 K and 28.5 K, respectively, with a small ordered moment (0.29−0.34µB ) along the c−axis, which is not an easy axis of the crystal field (CEF). In order to investigate how the moment direction and the spin gap energy change with 10% La doping in Ce1−xLaxT2Al10 (T = Ru and Os) and also to understand the microscopic nature of the magnetic ground state, we here report on magnetic, transport, and thermal properties, neutron diffraction (ND) and inelastic neutron scattering (INS) investigations on these compounds. Our INS study reveals the persistence of spin gaps of 7 meV and 10 meV in the 10% La-doped T = Ru and Os compounds, respectively. More interestingly our ND study shows a very small ordered moment of 0.18 µB along the b−axis (moment direction changed compared with the undoped compound), in Ce0.9La0.1Ru2Al10, however a moment of 0.23 µB still along the c−axis in Ce0.9La0.1Os2Al10. This contrasting behavior can be explained by a different degree of hybridization in CeRu2Al10 and CeOs2Al10, being stronger in the latter than in the former. Muon spin rotation (µSR) studies on Ce1−xLaxRu2Al10 (x = 0, 0.3, 0.5 and 0.7), reveal the presence of coherent frequency oscillations indicating a long−range magnetically ordered ground state for x = 0 to 0.5, but an almost temperature independent Kubo−Toyabe response between 45 mK and 4 K for x = 0.7. We will compare the results of the present investigations with those reported on the electron and hole−doping in CeT2Al10.

The lightly hole-doped system CeOs1.94Re0.06Al10 has been studied by muon spin relaxation and neutron diffraction measurements. A long-range antiferromagnetic ordering of the Ce-sublattice with substantially reduced value of the magnetic moment 0.18(1)µB has been found below TN = 21 K. Similar to the undoped parent compound, the magnetic ground state of CeOs1.94Re0.06Al10 preserves the anomalous direction of the ordered moments along the c-axis. The obtained result reveals the crucial difference between electron-and hole-doping effects on the magnetic ordering in CeOs2Al10. The former suppresses the anisotropic c − f hybridization and promotes localized Ce moments. On the contrary, the latter increases the hybridization and shifts the system towards delocalized non-magnetic state.PACS numbers: 75.25.-j Unusual magnetic order in the Kondo semiconductors CeOs 2 Al 10 and CeRu 2 Al 10 with an orthorhombic cage structure has attracted much attention in last few years.1-11 The order takes place at unexpectedly high temperature T N ∼ 29 K if one takes into account the large separation distance (∼ 5.2Å) between Ce ions in the structure and involvement of a very small ordered moment ∼ 0.3 -0.4µ B along the c-crystallographic direction 9,12,13 which is not the easy axis in the static susceptibility measurements above the transition temperature. In addition, a spin gap formation takes place at a temperature slightly higher T N in these materials as well as in the paramagnetic state of CeFe 2 Al 10 .7,11,14,15 The latter does not show any sign of magnetic order and the Ce ions in this compound are believed to be in the valence fluctuating regime. The mechanism providing the high ordering temperature and the gap formation has not been clarified yet. Based on optical conductivity measurements, Kimura et al.16 suggested a charge density wave as the primary instability which then induces the unusual magnetic ordering at T N . An indirect confirmation of this idea is the presence of the structural modulation with the (0, − 2 3 , 2 3 ) propagation vector revealed by electron diffraction in CeOs 2 Al 10 at 15 K.3 The critical temperature where this modulation comes in was not clarified and later X-ray and neutron diffraction measurements failed to find evidence of the symmetry lowering below and above T N . 9,11,12The reduced ordered moment found in the neutron diffraction experiments has been attributed by Strigari et al. 17,18 to the crystal field effects studied by polarizationdependent soft x-ray absorption measurements. The proposed ground state wave function provides quantitative agreement with the experimental data and has been confirmed by inelastic neutron scattering.19 The nature of the strongly anisotropic exchange parameters stabilizing the ordered state with the moments being along the caxis is however unclear so far.Very recently, a great sensitivity of CeRu 2 Al 10 and CeOs 2 Al 10 to electron-doping has been revealed. [20][21][22] In both compounds a small substitution with 4d and 5d transition metals carrying e...

The effects of electron (Ir) and hole (Re) doping on the hybridization gap and antiferromagnetic order have been studied by magnetization, muon spin relaxation (µ + SR), and inelastic neutron scattering on the polycrystalline samples of Ce(Os1−xIrx)2Al10 (x = 0.08 and 0.15) and CeOs1.94Re0.06Al10. µ + SR spectra clearly reveals magnetic ordering below 20 and 10 K for x = 0.08 and 0.15 samples respectively with a very weak signature of oscillations of the muon initial asymmetry at very short time scale. Our important findings are that small amount of electron doping (i) completely suppress the inelastic magnetic excitations near 11 meV down to 2K, which were observed in the undoped compound, and the response transforms into a broad quasielastic response and (ii) the internal field at the corresponding muon site is remarkably enhanced by about ten times compared with the parent compound. On the other hand with small amount of hole (3% Re) doping the intensity of the inelastic magnetic excitations near 11 meV is reduced significantly. The main origin of the observed doping effect is an extra 5d electrons being carried by Ir and a hole carried by Re compared with that the Os atom. The obtained results demonstrate a great sensitivity of the carrier doping and provides additional ways to study their anomalous magnetic properties.