Structural Modification and Metamagnetic Anomaly in the Ordered State of CeOs2Al10

A caged compound CeOs2Al10, crystallizing in the orthorhombic YbFe2Al10-type structure, undergoes a mysterious phase transition at T_0=29 K. We report the results of electron diffraction, magnetization, and magnetoresistance for single crystals. Superlattice reflections characterized by a wave vector q = (0, -2/3, 2/3) observed at 15 K indicate a structural modification in the ordered state. Activation-type behavior of the electrical resistivity along the three principal axes below 50 K suggests gap opening in the conduction band. The magnetic susceptibility \chi = M/B is highly anisotropic, \chi_a>\chi_c>\chi_b, all of which sharply decrease on cooling below T_0. Furthermore, a metamagnetic anomaly in the magnetization and a step in the magnetoresistance occur at B=6-8 T only when the magnetic field is applied parallel to the orthorhombic c axis. However, T_0 hardly changes under magnetic fields up to 14 T, irrespective of the field direction. By using these data, we present a B-T phase diagram and discuss several scenarios for the mysterious transition.Comment: 6 pages, 7 figures, accepted for publication in Phys. Rev.

Electronic-Structure-Driven Magnetic Ordering in a Kondo Semiconductor CeOs2Al10

We report the anisotropic changes in the electronic structure of a Kondo semiconductor CeOs$_2$Al$_{10}$ across an anomalous antiferromagnetic ordering temperature ($T_0$) of 29 K, using optical conductivity spectra. The spectra along the $a$- and $c$-axes indicate that a $c$-$f$ hybridization gap emerges from a higher temperature continuously across $T_0$. Along the b-axis, on the other hand, a different energy gap with a peak at 20 meV appears below 39 K, which is higher temperature than $T_0$, because of structural distortion. The onset of the energy gap becomes visible below $T_0$. Our observation reveals that the electronic structure as well as the energy gap opening along the b-axis due to the structural distortion induces antiferromagnetic ordering below $T_0$.Comment: 4 pages, 4 figure

Heavy-fermion weak-ferromagnet YbRhSb

A new Yb-based compound YbRhSb with the orthorhombic -TiNiSi-type structure has been synthesized. The magnetic-susceptibility, magnetization, and specific-heat (Cp) measurements of single crystals revealed a ferromagnetic transition at TC = 2.7 K. An extrapolation of the Cp/T data below 1 K yields 370 mJ/mol K2 as the value, and the magnetic entropy reaches only 0.25R ln 2 at TC. The spontaneous moment is unusually small, 3×10–3µB/Yb for B||b, while the magnetization increases to 1.4µB/Yb when the field of 15 T is applied along the a axis. We ascribe the weak ferromagnetism to a canted antiferromagnetic structure based on the observation of a metamagnetic transition and the decrease of TC with the increase of magnetic field

Multiple phosphorus chemical sites in heavily phosphorus-doped diamond

We have performed high-resolution core level photoemission spectroscopy on a heavily phosphorus (P)-doped diamond film in order to elucidate the chemical sites of doped-phosphorus atoms in diamond. P 2p core level study shows two bulk components, providing spectroscopic evidence for multiple chemical sites of doped-phosphorus atoms. This indicates that only a part of doped-phosphorus atoms contribute to the formation of carriers. From a comparison with band calculations, possible origins for the chemical sites are discussed

Optical study of charge instability in CeRu2Al10 in comparison with CeOs2Al10 and CeFe2Al10

The anisotropic electronic structure responsible for the antiferromagnetic transition in CeRu2Al10 at the unusually high temperature of T0=28 K was studied using optical conductivity spectra, Ce 3d x-ray photoemission spectra, and band calculation. It was found that the electronic structure in the ac plane is that of a Kondo semiconductor, whereas that along the b axis has a nesting below 32 K (slightly higher than T0). These characteristics are the same as those of CeOs2Al10 [ S. Kimura et al. Phys. Rev. Lett. 106 056404 (2011)]. The c-f hybridization intensities between the conduction and 4f electrons of CeRu2Al10 and CeOs2Al10 are weaker than that of CeFe2Al10, showing no magnetic ordering. These results suggest that the electronic structure with one-dimensional weak c-f hybridization along the b axis combined with two-dimensional strong hybridization in the ac plane causes charge-density wave (CDW) instability, and the CDW state then induces magnetic ordering

Analysis on photoemission spectrum of superconducting FeSe

In this paper, we present the result of soft X-ray photoemission spectroscopy and its comparison with the density functional calculation. Although local density approximation seems to be a good starting point for describing the electronic structure of FeSe, the simulated spectrum poorly reproduced the structure around E(B) = 2 eV. This result suggests the necessity of theoretical treatment beyond local density approximation

Interplay between crystal electric field and magnetic exchange anisotropies in the heavy-fermion antiferromagnet YbRhSb under pressure

We report the pressure effect on the magnetic ground state of the heavy-fermion (HF) canted antiferromagnet YbRhSb (orthorhombic ɛ-TiNiSi-type) by means of magnetization and resistivity measurements using a single crystal. At ambient pressure, this compound undergoes a transition at TM1=2.7 K into a canted antiferromagnetic (AF) state with a small spontaneous moment of 3×10-3 μB/Yb. With increasing pressure P above 1 GPa, another magnetic transition occurs at TM2 above TM1, and TM1(P) has a deep minimum of 2.5 K at 1.7 GPa. For P≥2 GPa, the canted AF structure changes to a ferromagnetic (FM) one, where a large moment 0.4 μB/Yb lies in the orthorhombic b-c plane and a metamagnetic transition occurs at B || a = 1.5 T. This unusual FM state below TM3≅4.3 K is ascribed to the balance between the single-ion crystalline electric field (CEF) anisotropy with easy direction || a and the intersite exchange interaction with easy b-c plane. Furthermore, we have investigated the pressure dependence of TM3 up to 20.4 GPa using electrical resistivity measurements. The structural stability under pressures up to 19 GPa was examined by x-ray diffraction. We find that TM3 above 2.5 GPa steeply increases up to about 7 K, showing a broad maximum and then slightly decreases with increasing pressure above 8 GPa, while the structure remains unchanged. We attribute the enhancement of TM3 above 2.5 GPa to an increase of the CEF anisotropy with respect to magnetic exchange anisotropy. Finally, we compare and discuss the volume dependence of magnetic phase diagram of YbRhSb with the isostructural HF ferromagnet YbNiSn