Search

Low-temperature and elastic properties of the quasicrystal approximant GdCd6 have been investigated by means of an ultrasonic measurement. Salient elastic anomalies were observed in the temperature and magnetic field dependence of the principal elastic constants, most probably being associated with the successive multiple magnetic phase transitions showing up at low temperatures. Based on the experimental data, a magnetic field vs temperature phase diagram was constructed. In a zero magnetic field, at least four phases appear to exist. However, the phase diagram both for the magnetic field applied for H// ⟨ 100 ⟩ and H// ⟨ 110 ⟩ is richer, and interestingly some phase boundaries correspond to the development of field-induced phases, leading to the intricate magnetic phase diagram possibly with multiple ordered phases. We discuss the elastic and electronic properties at low temperatures, and also the nature of the multiple magnetic phase transitions of GdCd6.

We report a systematic study of the $5d$-electron-doped system $\mathrm{Ce}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ir}}_{x})}_{2}{\mathrm{Al}}_{10}$ $(0\ensuremath{\le}x\ensuremath{\le}0.15)$. With increasing $x$, the orthorhombic $b$ axis decreases slightly while accompanying changes in $a$ and $c$ leave the unit cell volume almost unchanged. Inelastic neutron scattering, along with thermal and transport measurements, reveal that for the Kondo semiconductor ${\mathrm{CeFe}}_{2}{\mathrm{Al}}_{10}$, the low-temperature energy gap, which is proposed to be a consequence of strong $c\text{\ensuremath{-}}f$ hybridization, is suppressed by a small amount of Ir substitution for Fe and that the system adopts a metallic ground state with an increase in the density of states at the Fermi level. The charge or transport gap collapses (at $x=0.04$) faster than the spin gap with Ir substitution. Magnetic susceptibility, heat capacity, and muon spin relaxation measurements demonstrate that the system undergoes long-range antiferromagnetic order below a N\'eel temperature ${T}_{\mathrm{N}}$ of 3.1(2) K for $x=0.15$. The ordered moment is estimated to be smaller than 0.07(1) ${\ensuremath{\mu}}_{\mathrm{B}}$/Ce, although the trivalent state of Ce is confirmed by Ce ${L}_{3}$-edge x-ray absorption near edge spectroscopy. It is suggested that the $c\text{\ensuremath{-}}f$ hybridization gap, which plays an important role in the unusually high ordering temperatures observed in $\mathrm{Ce}{T}_{2}{\mathrm{Al}}_{10}$ ($T$ = Ru and Os), may not be necessary for the onset of magnetic order with a low ${T}_{\mathrm{N}}$ seen here in $\mathrm{Ce}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ir}}_{x})}_{2}{\mathrm{Al}}_{10}$.

Kondo semiconductors based on rare-earth elements possess a narrow gap in the renormalised density of states near the Fermi level. Their ground states remain nonmagnetic due to strong hybri...

The dynamic magnetic properties of the Kondo-insulator state in $\mathrm{Ce}{\mathrm{Fe}}_{2}{\mathrm{Al}}_{10}$ (spin gap, resonance mode) have been investigated using polarized neutrons on a single crystal of pure $\mathrm{Ce}{\mathrm{Fe}}_{2}{\mathrm{Al}}_{10}$. The results indicate that the magnetic excitations are polarized mainly along the orthorhombic $a$ axis and their dispersion along the orthorhombic $c$ direction could be determined. Polycrystalline samples of Nd- and Rh-doped $\mathrm{Ce}{\mathrm{Fe}}_{2}{\mathrm{Al}}_{10}$ were also studied by the time-of-flight technique, with the aim of finding out how the low-energy magnetic excitation spectra change upon isoelectronic substitution of a rare-earth element (Nd) on the magnetic Ce site or electron doping (Rh) on the transition-element Fe sublattice. The introduction of magnetic Nd impurities strongly modifies the spin gap in the Ce dynamic magnetic response and causes the appearance of a quasielastic signal. The crystal-field excitations of Nd, studied in both $\mathrm{La}{\mathrm{Fe}}_{2}{\mathrm{Al}}_{10}$ and $\mathrm{Ce}{\mathrm{Fe}}_{2}{\mathrm{Al}}_{10}$, also reveal a significant influence of $f$-electron hybridization (largest in the case of Ce) on the crystal-field potential. As a function of the Rh concentration, a gradual change is observed from a Kondo-insulator to a metallic Kondo-lattice response, likely reflecting the decrease in the hybridization energy.

We have investigated the magnetic properties of a polycrystalline sample of NdOs2Al10 using neutron diffraction and inelastic neutron scattering, magnetic susceptibility and heat capacity measurements. The magnetic susceptibility data reveal an antiferromagnetic transition at T N1 = 2.2 K while the heat capacity data which extend to lower temperatures show a further transition at T N2 = 1.1 K. The INS measurements detect four well-resolved crystal field excitations at 7.4, 12.4, 17.6 meV and 19.2 meV at 5 K. The positions and intensities of the observed CEF excitations and the temperature dependence of previously published single crystal susceptibility data are analysed based on the orthorhombic CEF model of the J = 9/2 ground state multiplet of Nd3+ ion. The neutron diffraction study reveals the magnetic structure at T = 1.6 K to be of sine wave type (κ = [0, 0.723, 0]) with an ordered state moment of μ Nd 3+ = 1.59(1) μ B aligned along the a-axis in agreement with the single ion crystal field anisotropy. This indicates that the magnetism of NdOs2Al10 is governed by the RKKY interactions in agreement with other RT 2Al10 (R = Nd, Sm, Tb, T = Fe, Ru and Os), but different to that of R = Ce based compounds where anisotropic two ions interaction as well as Kondo interaction govern the anomalous direction of the ordered state moment.

The recent discovery of topological Kondo insulating behaviour in strongly correlated electron systems has generated considerable interest in Kondo insulators both experimentally and theoretically. The Kondo semiconductors CeT2Al10 (T=Fe, Ru and Os) possessing a c-f hybridization gap have received considerable attention recently because of the unexpected high magnetic ordering temperature of CeRu2Al10 (TN=27 K) and CeOs2Al10 (TN=28.5 K) and the Kondo insulating behaviour observed in the valence fluctuating compound CeFe2Al10 with a paramagnetic ground state down to 50 mK. We are investigating this family of compounds, both in polycrystalline and single crystal form, using inelastic neutron scattering to understand the role of anisotropic c-f hybridization on the spin gap formation as well as on their magnetic properties. We have observed a clear sign of a spin gap in all three compounds from our polycrystalline study as well as the existence of a spin gap above the magnetic ordering temperature in T=Ru and Os. Our inelastic neutron scattering studies on single crystals of CeRu2Al10 and CeOs2Al10 revealed dispersive gapped spin wave excitations below TN. Analysis of the spin wave spectrum reveals the presence of strong anisotropic exchange, along the c-axis (or z-axis) stronger than in the ab-plane. These anisotropic exchange interactions force the magnetic moment to align along the c-axis, competing with the single ion crystal field anisotropy, which prefers moments along the a-axis. In the paramagnetic state (below 50 K) of the Kondo insulator CeFe2Al10, we have also observed dispersive gapped magnetic excitations which transform into quasi-elastic scattering on heating to 100 K. We will discuss the origin of the anisotropic hybridization gap in CeFe2Al10 based on theoretical models of heavy-fermion semiconductors.

We have measured the strain, magnetization, and specific heat of the antiferromagnetic (AFM) Kondo semiconductors $\mathrm{Ce}{T}_{2}\mathrm{A}{\mathrm{l}}_{10}$ ($T=\mathrm{Ru}$ and Os) under uniaxial pressures applied along the orthorhombic axes. We found a linear dependence of ${T}_{\mathrm{N}}$ on the $b$-axis parameter for both compounds under uniaxial pressure $P\ensuremath{\parallel}b$ and hydrostatic pressure. This relation indicates that the distance between the Ce-$T$ layers along the $b$ axis is the key structural parameter determining ${T}_{\mathrm{N}}$. Furthermore, the pressure dependence of the spin-flop transition field indicates that Ce-Ce interchain interactions stabilize the AFM state with the ordered moments pointing to the $c$ axis.

The Kondo semiconductors $\mathrm{Ce}{T}_{2}\mathrm{A}{\mathrm{l}}_{10}$ ($T=\mathrm{Ru}$ and Os) exhibit antiferromagnetic (AFM) orders at unexpectedly high temperatures ${T}_{\mathrm{N}}=27.0$ and 28.5 K, respectively, whose mechanism remains in debate. We report the break-junction experiments on $4f/5d$-hole and $5d$-electron doped $\mathrm{CeO}{\mathrm{s}}_{2}\mathrm{A}{\mathrm{l}}_{10}$ as well as nondoped $\mathrm{CeR}{\mathrm{u}}_{2}\mathrm{A}{\mathrm{l}}_{10}$. The differential conductance spectra $dI/dV$ for $T=\mathrm{Os}$ and Ru show three gap structures; two hybridization gaps ${V}_{1}, {V}_{2}$ and an AFM gap ${V}_{\mathrm{AF}}$, whose magnitudes for $T=\mathrm{Os}$ are $15\ensuremath{-}50%$ larger than for $T=\mathrm{Ru}$. Doping of $4f/5d$ holes and $5d$ electrons in $\mathrm{CeO}{\mathrm{s}}_{2}\mathrm{A}{\mathrm{l}}_{10}$ changes the $dI/dV$ spectrum in very different ways. Nevertheless, in all cases, the suppression of ${V}_{1}$ is well correlated with those of ${V}_{\mathrm{AF}}$ and ${T}_{\mathrm{N}}$. Furthermore, the zero-bias conductance decreases on cooling below ${T}^{*}$ ($g{T}_{\mathrm{N}}$) only in the doping region where ${V}_{1}$ and ${V}_{\mathrm{AF}}$ coexist. This fact indicates that the unusual AFM order is preceded by the decrease in the density of states in the presence of ${V}_{1}$.

We succeeded in synthesizing single crystals of the tetragonal antiferromagnet CeCoSi, which shows an anomalous pressure induced ordered phase (PIOP) with an extraordinary high transition temperatu...

We report a single-crystal study on the Kondo semiconductor CeFe2Al10 in which we measured the magnetic susceptibility, electrical resistivity, thermopower and thermal conductivity. The highly anisotropic behavior in all measurements indicates an anisotropic electronic structure that could originate from a c–f hybridization in an orthorhombic YbFe2Al10-type structure. The anisotropic c–f hybridization effect is manifested in the different peak temperatures of the electrical resistivity and the thermopower along the three principal axes.

We present bulk-sensitive hard x-ray photoelectron spectroscopy (HAXPES) data of the Ce3d core levels and lifetime-reduced L edge x-ray absorption spectroscopy (XAS) in the partial fluorescence yield (PFY) mode of the CeMIn5 family with M = Co, Rh, and Ir. The HAXPES data are analyzed quantitatively with a combination of full multiplet and configuration interaction model which allows correcting for the strong plasmons in the CeMIn5 HAXPES data, and reliable weights wn of the different fn contributions in the ground state are determined. The CeMIn5 results are compared to HAXPES data of other heavy fermion compounds and a systematic decrease of the hybridization strength Veff from CePd3 to CeRh3B2 to CeRu2Si2 is observed, while it is smallest for the three CeMIn5 compounds. The f-occupation, however, increases in the same sequence and is close to one for the CeMIn5 family. The PFY-XAS data confirm an identical f-occupation in the three CeMIn5 compounds and a phenomenological fit to these PFY-XAS data combined with a configuration interaction model yields consistent results., 9 pages, 5 figures

The La-substitution and pressure effects on antiferromagnet CeCoSi with a tetragonal crystal structure were investigated in order to clarify the origin of the pressure induced ordered phase (PIOP) with an enormously high transition temperature of T0 ∼ 38 K. By substituting Ce with La, the PIOP shifts to high pressures, and the maximum value of T0 is suppressed, indicating that the PIOP originates from a Ce–Ce interaction. At T0, the magnetic susceptibility exhibits not a cusp, but an increase with decreasing temperature, as is frequently observed in antiferroquadrupolar (AFQ) ordering. Based on these results, we propose that a possible origin of the PIOP is an AFQ ordered phase of Ce-4f electron. Due to the lack of local inversion symmetry at the Ce sites, the AFQ order could be accompanied by odd parity multipolar moments. Since there is no clear evidence of successive transitions below T0, the remaining Kramers degeneracy could be lifted by the Kondo coupling.

Resonant polarised soft x-ray scattering at the cerium M-edge has been used to refine the magnetic structure of CeRu2Al10. A strong resonant feature at the cerium MIV-edge was observed at the disallowed \((0,1,0)\) Bragg position, consistent with previous neutron diffraction refinement of the moment pointing along the c-axis. The magnetic peak was found to have a temperature dependence expected for the paramagnetic–antiferromagnetic transition, disappearing above around 30 K. The polarisation dependence of the scattered x-rays conclusively shows that the low-temperature antiferromagnetic structure is non-collinear in nature. Fitting the polarisation dependence of the obtained Stokes parameters was undertaken with models for canting along either the a-axis or the b-axis. The experimental data agrees better with the model involving canting towards the a-axis. However, this is inconsistent with the Cmcm space group, suggestive of a symmetry lowering to either Pmnm or Cm2m. The resulting model is then achieve...

${\mathrm{CeOs}}_{2}{\mathrm{Al}}_{10}$ exhibits Kondo semiconducting properties, yet orders antiferromagnetically at a rather high temperature, ${T}_{\mathrm{N}}=28.5$ K. We have performed break-junction tunneling measurements on single crystals of ${\mathrm{CeOs}}_{2}{\mathrm{Al}}_{10}$ and the nonmagnetic Kondo semiconductor ${\mathrm{CeFe}}_{2}{\mathrm{Al}}_{10}$. Upon cooling ${\mathrm{CeFe}}_{2}{\mathrm{Al}}_{10}$, two hybridization gaps successively appear in the tunneling spectra, while another gap opens in ${\mathrm{CeOs}}_{2}{\mathrm{Al}}_{10}$ below ${T}_{\mathrm{N}}$. For both compounds, the ratio of the two hybridization gap widths is approximately 4, in agreement with the hybridization gap model for the crystal-field ground state of ${\mathrm{Ce}}^{3+}$ with $|{J}_{z}\ensuremath{\rangle}=|\ifmmode\pm\else\textpm\fi{}3/2\ensuremath{\rangle}$. Furthermore, we found that the gap widths are well scaled by the Kondo temperature among Ce-based Kondo semimetals/semiconductors with orthorhombic structures.

The opening of a spin gap in the orthorhombic compounds CeT$_2$Al$_{10}$ (T = Ru and Os) is followed by antiferromagnetic ordering at $T_N$ = 27 K and 28.5 K, respectively, with a small ordered moment (0.29$-$0.34$\mu_B$) 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 Ce$_{1-x}$La$_x$T$_2$Al$_{10}$ (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 $\mu_B$ along the $b-$axis (moment direction changed compared with the undoped compound), in Ce$_{0.9}$La$_{0.1}$Ru$_2$Al$_{10}$, however a moment of 0.23 $\mu_B$ still along the $c-$axis in Ce$_{0.9}$La$_{0.1}$Os$_2$Al$_{10}$. This contrasting behavior can be explained by a different degree of hybridization in CeRu$_2$Al$_{10}$ and CeOs$_2$Al$_{10}$, being stronger in the latter than in the former. Muon spin rotation ($\mu$SR) studies on Ce$_{1-x}$La$_x$Ru$_2$Al$_{10}$ ($x$ = 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 CeT$_2$Al$_{10}$.

A Kondo semiconductor ${\mathrm{CeRu}}_{2}{\mathrm{Al}}_{10}$ with an orthorhombic crystal structure shows unusual antiferromagnetic ordering at a rather high temperature ${T}_{0}$ of 27.3 K, which is lower than the Kondo temperature ${T}_{\mathrm{K}}\ensuremath{\sim}60$ K. In optical conductivity [$\ensuremath{\sigma}(\ensuremath{\omega})$] spectra that directly reflect the electronic structure, a $c\text{\ensuremath{-}}f$ hybridization gap between the conduction and $4f$ states is observed at around 40 meV along the three principal axes. However, an additional peak at around 20 meV appears only along the $b$ axis. By increasing $x$ to 0.05 in $\mathrm{Ce}{({\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{x})}_{2}{\mathrm{Al}}_{10}$, the ${T}_{0}$ decreases slightly from 27.3 to 24 K, but the direction of the magnetic moment changes from the $c$ axis to the $a$ axis. Thereby, the $c\text{\ensuremath{-}}f$ hybridization gap in the $\ensuremath{\sigma}(\ensuremath{\omega})$ spectra is strongly suppressed, but the intensity of the 20 meV peak remains as strong as for $x=0$. These results suggest that the change in the magnetic moment direction originates from a decrease in the $c\text{\ensuremath{-}}f$ hybridization intensity. The magnetic ordering temperature ${T}_{0}$ is not directly related to $c\text{\ensuremath{-}}f$ hybridization but is related to the charge excitation at 20 meV observed along the $b$ axis.

Low-temperature properties of a heavy fermion compound YbAgGe have been investigated by electrical resistivity, specific heat and magnetization measurements on a single crystalline sample. This compound, crystallizing in the hexagonal ZrNiAl-type structure, undergoes two magnetic phase transitions at T M1 =0.8 K (second order) and T M2 =0.65 K (first order). Below T M2 , the jump of the resistivity along the a axis indicates gap formation on the Fermi surface along the a axis. The extremely small magnetic entropy of 0.6 J/mol K released at T M1 is attributed to the combination of the Kondo effect and magnetic frustration effect. When the magnetic field B ∥ a is increased to 5 T, T M1 is depressed to 0 K. At this critical magnetic field, the magnetic susceptibility χ follows the Curie–Weiss law, χ -1 -χ 0 -1 ∝ T , in a wide temperature range from 0.45 K to 300 K.

We have studied the valence states and thermoelectric properties of Yb2T3Sn5 (T = Pt and Pd) with two inequivalent Yb sites. For Yb2Pt3Sn5, the 4f -hole occupation number nf is estimated to be 0.4 at 300 K from the magnetic susceptibility and LIII-edge absorption spectrum. Intermediate-valence behaviors manifest themselves in a largely negative value of the paramagnetic Curie temperature, � 216 K, a broad peak at 300 K in the magnetic part of the resistivity, and a large minimum in the thermopower, � 38 mV/K at 60 K. The specific heat shows no transition down to 0.6 K. These results are explained by a model in which Yb ions in one site are divalent and those in the other site are in a valence fluctuating state with a Kondo temperature of 200 K. Thus, Yb2Pt3Sn5 is a rare example of the heterogeneous mixed-valence system. An isostructural compound Yb2Pd3Sn5 has a larger unit-cell volume by 2.4%, which allows the Yb ions in both the sites to be divalent.

The thermoelectric properties of the binary quasicrystal Cd84.6Yb15.4 and its approximant Cd6Yb are reported. The thermopowers decrease linearly from 14 and 12 µV/K, respectively, with decreasing temperature from 300 K. The resistivities at 300 K are 180 and 150 µΩcm, respectively, and decrease rapidly on cooling below 100 K. These results indicate that Cd–Yb compounds possess a metallic nature, in contrast to the semiconductor-like behavior of conventional ternary quasicrystals. The phonon thermal conductivity κph(T) of Cd–Yb compounds shows no maximum, but is described by a power law, κph∝Tn, with n=0.5 and 1.0, respectively, for Cd84.6Yb15.4 and Cd6Yb. The thermoelectric dimensionless figures of merit ZT are estimated to be 0.003 and 0.004 at 300 K, respectively.

We have studied the effects of dilution of Ce sublattice on the unusual antiferromagnetic (AFM) order in the Kondo semiconductor CeOs2Al10 at 28.5 K by the magnetic, transport and specific-heat measurements of single crystals of Ce1-zLazOs2Al10. The effective magnetic moment and paramagnetic Curie temperature hardly change with z up to 0.5, indicating that the 4f state remains unchanged at high temperatures. The suppression of the Neel temperature TN is much weaker than that in 5d hole doped system, Ce(Os1-yRey)2Al10. Therefore, the AFM interaction is robust against the violation of the coherent Ce sublattice. The activation energy in the resistivity decreases in parallel with TN, confirming the argument that the presence of the c-f hybridization gap is a requisite for the unusual AFM order in this system.

The Kondo semiconductor CeOs2Al10 undergoes an antiferromagnetic (AFM) order at an unexpectedly high temperature 28.5 K. We have performed break junction tunneling measurements for the hole-doped system Ce(Os1-yRey)2Al10 (y ≤ 0.1). The tunneling spectrum dI/dV for y = 0 displays successive openings of a hybridization gap V1, an AFM gap VAF and another hybridization gap V2 in the density of states (DOS). On cooling from 36 K to TN, both the gap value V1 and the DOS at the Fermi level, EF, decrease by 8% of the values at 36 K. This fact indicates that the development of short-range magnetic correlations reduces the c-f hybridization gap. For y = 0.02, a peak appears in dI/dV at V = 0 concurrently with the disappearance of V2. With increasing y further, the in-gap states develop at EF, in good agreement with the increase in the Sommerfeld coefficient of the heat capacity. Thereby, TN, V1 and VAF decrease and disappear at y = 0.05. These facts provide compelling evidence that the presence of V1 is necessary for the AFM order in CeOs2Al10.

We have studied the relation between the unusual antiferromagnetic (AFM) ordering and anisotropic c-f hybridization in CeOs2Al10 by measuring the magnetic susceptibility χ under uniaxial pressures P up to 0.45 GPa. For P // B // a and P // B // c, the AFM ordering temperature TN = 28.5 K hardly changes with increasing P, while the value of χ decreases and the maximal temperature of χ(T) shifts to higher temperatures. These findings suggest that the intensity of c-f hybridization is enhanced along the pressurized a and c axes. On the other hand, for P // b, TN increases up to 30 K at 0.15 GPa, while the value of χ remains unchanged. This observation for P // b suggests that the net intensity of c-f hybridization decreases, while the c-f hybridization along the b-axis hardly changes. We discuss these results in terms of the atomic displacements of Os, Al(3) and Al(4) under uniaxial pressures.

We have measured the electrical resistivity (ρ), the Hall coefficient (RH) and transverse magnetoresistance (MR) of single crystals for heavy-fermion ferromagnet CeAgSb2. These quantities are strongly anisotropic reflecting the two-dimensional electronic structure. At higher temperature, temperature dependence of ρ and RH are dominated by the impurity Kondo scattering. Anomalous positive contribution is observed in MR for j//c-axis and H//a-axis around 30K, which is not explainable by the usual orbital magnetoresistance.

The Kondo semiconductor ${\text{CeOs}}_{2}$${\text{Al}}_{10}$ exhibits an antiferromagnetic (AFM) order at ${T}_{\mathrm{N}}=28.5$ K, whose temperature is unexpectedly high for the small ordered moment of ${\ensuremath{\mu}}_{\mathrm{AF}}=0.3$${\ensuremath{\mu}}_{\mathrm{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 $\ensuremath{\chi}$, electrical resistivity $\ensuremath{\rho}$, and specific heat $C$ on single crystals of Ce(${\text{Os}}_{1\ensuremath{-}x}$${\text{Ir}}_{x}$)${}_{2}$${\text{Al}}_{10}$($x\ensuremath{\le}0.15$) and Ce(${\text{Os}}_{1\ensuremath{-}y}$${\text{Re}}_{y}$)${}_{2}$${\text{Al}}_{10}$($y\ensuremath{\le}0.1$). The results of $M(B)$ indicate that the direction of ${\ensuremath{\mu}}_{\mathrm{AF}}$ changes from the $c$ axis for $x=0$ to the $a$ axis for $x=0.03$. With increasing $x$ up to 0.15, ${T}_{\mathrm{N}}$ gradually decreases although the $4f$ electron state becomes localized and the magnitude of ${\ensuremath{\mu}}_{\mathrm{AF}}$ is increased to 1${\ensuremath{\mu}}_{\mathrm{B}}/$Ce. With increasing $y$, on the contrary, 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 ${T}_{\mathrm{N}}$ is well correlated with the increase of the Sommerfeld coefficient $\ensuremath{\gamma}$ in $C(T)$. Furthermore, the simultaneous suppression of ${T}_{\mathrm{N}}$ and the semiconducting gap in $\ensuremath{\rho}(T)$ at $Tg{T}_{\mathrm{N}}$ indicates that the presence of the hybridization gap is necessary for the unusual AFM order in ${\text{CeOs}}_{2}$${\text{Al}}_{10}$.

A combination of the dense Kondo effect and Ruderman–Kittel–Kasuya–Yoshida interaction exhibited by an antiferromagnetic (AF) heavy-Fermion compound CeCuSb 2 ( T N =8 K) was investigated with the magnetic susceptibility χ and 63 Cu magnetic resonance measurements in the temperature range between 1.4 and 210 K. For temperatures above ∼25 K, characteristics of the localized 4 f spins are observed in the Curie–Weiss-type behavior of the Knight shift K and the strongly enhanced relaxation rate T 1 -1 . For the temperature below ∼25 K, the χ data tend toward a constant value, which is an indication of the onset of the heavy-Fermion state. The slope of the Knight shift versus susceptibility ( K -χ) plots decreases below ∼100 K, which is ascribed to the difference in the anisotropic hyperfine coupling to the crystal-field-split Γ 7 (ground state) and Γ 8 (excited state) wave functions of the Ce ions. The K -χ plots below ∼25 K exhibit another deviation from the linearity in opposite direction. We speculate that ...

The resonant inverse photoemission study (RIPES) at the Ce $4\stackrel{\ensuremath{\rightarrow}}{d}4f$ absorption edge of ${\mathrm{CeRh}}_{3},$ ${\mathrm{CePd}}_{3},$ and ${\mathrm{CeSn}}_{3}$ has been carried out. The RIPES spectra show the wide variety of the $4f$ electron character in these compounds, indicating the characteristic Kondo temperature and $4f$ electron number. The excitation energy dependence of $4f$-spectral resonance, especially in ${4f}^{2}$ final-state structure, indicates a large $4d\ensuremath{-}4f$ multiplet splitting and strict selection rule in the final state of the RIPES process. Constant final-state spectra of the ${f}^{1}$ final state show the $4f$ spin-orbit splitting components. A calculation is carried out by the impurity Anderson model with full multiplet effects and explains well the excitation energy dependence of the RIPES spectra.

Specific-heat, magnetic-susceptibility and electrical-resistivity measurements were carried out on four Ce compounds of tetragonal BaNiSn 3 -type, CeTSi 3 and CeTGe 3 ( T= Rh and Ir). All these compounds show magnetic transitions at low temperatures. CeRhSi 3 and CeIrSi 3 are a Kondo-lattice compound with a relatively high Kondo temperature of the order of 100 K, while CeRhGe 3 and CeIrGe 3 exhibit a very weak Kondo effect, and three magnetic phase transitions below 14.6 K and 8.7 K, respectively. These contrasting behaviors in the silicides and germanides are discussed by comparing with properties of other BaNiSn 3 -type Ce compounds, like CeFeGe 3 and CeCoGe 3 .

We have investigated several ternary compounds of cerium in the Ce-Pd-X (X=Si, Ge and Al) systems and their La counterparts by measuring the magnetic susceptibility, electrical resistivity and specific heat. The Ce ions in these compounds are in the nearly trivalent state and most of them show magnetic order of either long-range or spin-glass type at low temperatures. None of them distinctly exhibits the heavy fermion behavior, although it may be obscured by atomic disorder in some compounds. The relation between several isostructural ternary compounds of Ce-Pd-(Si and Ge) or Ce-Pd-(Al and Ga) system is qualitatively discussed in the framework of the Doniach phase diagram. The variation of the unit cell volume suggests that the former group is consistent with this phase diagram but the latter is not seemingly so. We found that LaPdSi 3 and LaPd 0.6 Ge 1.4 among the La counterparts are superconducting below 2.6 and 2.8 K, respectively.

We have investigated the magnetic and transport properties of RTSb 2 (R=La and Ce: T=Ni, Cu, Pd and Ag) by magnetic susceptibility, electrical resistivity and specific heat. These compounds crystallize in the ZrCuSi 2 -type structure and the resistivity of each Ce compound shows dense Kondo-type behavior. For CeCuSb 2 and CeAgSb 2 , magnetic order was found at 8 and 10 K, respectively. Other Ce compounds did not show any transition down to 0.5 K, while a superconducting transition was found in LaTSb 2 (T=Ni, Cu and Pd) at 1.0, 0.9 and 2.7 K, respectively.

We report the measurements of resistivity ρ , specific heat C, and magnetization M on single crystals of the heavy-fermion weak-ferromagnet YbRhSb ( T M = 2.7 K ) in various magnetic fields B as well as ρ ( T ) under pressures. Both the decrease of T M with increasing B and the peaking of M / B at T M in modest fields confirm that the weak ferromagnetism is the consequence of canted antiferromagnetism. For B ∥ a , T M disappears at B C = 5 T . Above B C , ρ , C and M/B show a Fermi-liquid behavior. The results of ρ ( T ) under pressures reveal a broad maximum and a deep minimum of T M ( P ) at 0.8 and 1.6 GPa, respectively. This minimum suggests the competition of distinct-type of magnetic interactions.

We report the measurements of electrical resistivity ρ under various pressures for the single crystal of a heavy-fermion compound YbAgGe. This compound undergoes two magnetic phase transitions at T M 1 = 0.8 K (second order) and T M 2 = 0.65 K (first order). With applying pressure above 0.5 GPa, the resistive anomalies at T M 1 and T M 2 merge into a sharp drop at T M . In the range 0.5 P 1.5 GPa , T M is constant, whereas the concomitant increase of ρ ( 0.5 K ) suggests the development of spin fluctuations. For P > 1.5 GPa , ρ ( 0.5 K ) largely decreases and the anomaly in ρ ( T = T M ) becomes broader and shifts to higher temperatures. These significant changes at 1.5 GPa suggest a transition from a small-moment ordered state to a stable magnetic state with suppressed spin fluctuations.

Magnetic susceptibility and specific heat measurements on quasicrystalline approximants Au-Si-Gd and Au-Ge-Gd reveal that a ferromagnetic (FM) transition occurs at Tc = 22.5(5) K for Au-Si-Gd and at Tc = 13(1) K for Au-Ge-Gd, which are the first examples of ferromagnetism in crystalline approximants. In addition, a re-entrant spin-glass (RSG) transition is observed at TRSG = 3.3 K for Au-Ge-Gd in contrast to Au-Si-Gd. The different behaviors are understood based on the recent structural models reported by Gebresenbut et al (2013 J. Phys.: Condens. Matter 25 135402). The RSG transition in Au-Ge-Gd is attributed to a random occupation of the center of the Gd12 icosahedron by Gd atoms; a central Gd spin hinders the long-range FM order.

We report the nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements for non-centrosymmetric superconductors Re7B3, LaBiPt, and BiPd containing heavy elements. For all three compounds, the spin-lattice relaxation rate 1/T1 shows a coherence peak just below Tc and decreases exponentially at low temperatures, which indicates that an isotropic superconducting gap is dominant in these compounds. In BiPd, the height of the coherence peak just below Tc is much suppressed, which suggests that there exists a substantial component of gap with nodes in this compound. Our results indicate that heavy element is not the only factor, but the extent of inversion symmetry breaking is also important to induce a large spin-orbit coupling and an unconventional superconducting state., 11 pages, 7 figures

We have carried out muon spin relaxation (mu SR), neutron diffraction, and inelastic neutron scattering (INS) investigations on polycrystalline samples of Ce(Ru1-xFex)(2)Al-10 (x = 0, 0.3, 0.5, 0.8, and 1) to investigate the nature of the ground state (magnetic ordered versus paramagnetic) and the origin of the spin-gap formation as evident from the bulk measurements in the end members. Our zero-field mu SR spectra clearly reveal coherent two-frequency oscillations at low temperature in x = 0, 0.3, and 0.5 samples, which confirm the long-range magnetic ordering of the Ce moment with Neel temperature T-N = 27, 26, and 21 K, respectively. On the other hand, the mu SR spectra of x = 0.8 and x = 1 down to 1.4 K and 0.045 K, respectively, exhibit a temperature-independent Kubo-Toyabe term, confirming a paramagnetic ground state. The long-range magnetic ordering in x = 0.5 below 21 K has been confirmed through the neutron diffraction study. INS measurements of x = 0 clearly reveal the presence of a sharp inelastic excitation near 8 meV between 5 K and 26 K, due to an opening of a gap in the spin excitation spectrum, which transforms into a broad response at and above 30 K. Interestingly, at 4.5 K, the spin-gap excitation broadens in x = 0.3 and exhibits two clear peaks at 8.4(3) and 12.0(5) meV in x = 0.5. In the x = 0.8 sample, which remains paramagnetic down to 1.2 K, there is a clear signature of a spin gap of 10-12 meV at 7 K, with a strong wave-vector-dependent intensity. Evidence of a spin gap of 12.5(5) meV has also been found in x = 1. The observation of a spin gap in the paramagnetic samples (x = 0.8 and 1) is an interesting finding in this study, and it challenges our understanding of the origin of the semiconducting gap in CeT2Al10 (T = Ru and Os) compounds in terms of a hybridization gap opening only a small part of the Fermi surface, gapped spin waves, or a spin-dimer gap. (Less)