Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA crossover from Kondo semiconductor to metallic antiferromagnet with $5d$-electron doping in CeFe$_2$Al$_{10}$
133
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report a systematic study of the $5d$-electron-doped system Ce(Fe$_{1-x}$Ir$_x$)$_2$Al$_{10}$ ($0 leq x leq 0.15$). 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 CeFe$_2$Al$_{10}$, the low-temperature energy gap which is proposed to be a consequence of strong $c mhyphen f$ 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 Neel 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)~$mu_mathrm{B}$/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 $c mhyphen f$ hybridization gap, which plays an important role in the unusually high ordering temperatures observed in Ce$T_2$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 Ce(Fe$_{1-x}$Ir$_x$)$_2$Al$_{10}$.
rate research
Read More
Magnetic ground state of Rh-doped Kondo semiconductor CeRu$_2$Al$_{10}$ [Ce(Ru$_{1-x}$Rh$_x$)$_2$Al$_{10}$] is investigated by muon-spin relaxation method. Muon-spin precession with two frequencies is observed in the $x$ = 0 sample, while only one frequency is present in the $x$ = 0.05 and 0.1 samples, which is attributed to the broad static field distribution at the muon site. The internal field at the muon site is enhanced from about 180 G in $x$ = 0 sample to about 800 G in the Rh-doped samples, supporting the spin-flop transition as suggested by macroscopic measurements, and the boundary of different magnetic ground states is identified around $x$ = 0.03. The drastic change of magnetic ground state by a small amount of Rh-doping (3%) indicates that the magnetic structure in CeRu$_2$Al$_{10}$ is not robust and can be easily tuned by external perturbations such as electron doping. The anomalous temperature dependence of internal field in CeRu$_2$Al$_{10}$ is suggested to be attributed to the hyperfine interaction between muons and conduction electrons.
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$_{10}$.
The Kondo semiconductor CeOs$_{2}$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 $0.3$ $mu_mathrm{B}/$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 $chi$, electrical resistivity $rho$, and specific heat $C$ on single crystals of Ce(Os$_{1-x}$Ir$_{x}$)$_{2}$Al$_{10}$($x le 0.15$) and Ce(Os$_{1-y}$Re$_{y}$)$_{2}$Al$_{10}$($y le 0.1$). The results of $M (B)$ indicates that the AFM ordered moment $mu_mathrm{AF}$ changes the direction 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 $mu_mathrm{AF}$ is increased to $1$ $mu_mathrm{B}/$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 $T_mathrm{N}$ is well correlated with the increase of the Sommerfeld coefficient $gamma$ in $C(T)$. Furthermore, the simultaneous suppression of $T_mathrm{N}$ and the semiconducting gap in $rho (T)$ at $T > T_mathrm{N}$ indicates that the presence of the hybridization gap is indispensable for the unusual AFM order in CeOs$_{2}$Al$_{10}$.
An anisotropic Kondo semiconductor CeOs$_2$Al$_{10}$ exhibits an unusual antiferromagnetic order at rather high transition temperature $T_0$ of 28.5 K. Two possible origins of the magnetic order have been proposed so far, one is the Kondo coupling of the hybridization between the conduction ($c$) and the $4f$ states and the other is the charge-density wave/charge ordering along the orthorhombic $b$ axis. To clarify the origin of the magnetic order, we have investigated the electronic structure of hole- and electron-doped CeOs$_2$Al$_{10}$ [Ce(Os$_{1-y}$Re$_y$)$_2$Al$_{10}$ and Ce(Os$_{1-x}$Ir$_x$)$_2$Al$_{10}$, respectively] by using optical conductivity spectra along the $b$ axis. The intensity of the $c$-$f$ hybridization gap at $hbaromegasim50$ meV continuously decreases from $y=0.10$ to $x=0.12$ via $x=y=0$. The intensity of the charge excitation observed at $hbaromegasim20$ meV has the maximum at $x=y=0$ as similar with the doping dependence of $T_{rm 0}$. The fact that the charge excitation is strongly related to the magnetic order strengthens the possibility of the charge density wave/charge ordering as the origin of the magnetic order.
Understanding the electron dynamics and transport in metallic and semiconductor nanostructures -- such as metallic nanoparticles, thin films, quantum wells and quantum dots -- represents a considerable challenge for todays condensed matter physics, both fundamental and applied. In this review article, we will describe the collective electron dynamics in metallic and semiconductor nanostructures using different, but complementary, approaches. For small excitations (linear regime), the spectral properties can be investigated via quantum mean-field models of the TDLDA type (time-dependent local density approximation), generalized to account for a finite electron temperature. In order to explore the nonlinear regime (strong excitations), we will adopt a phase-space approach that relies on the resolution of kinetic equations in the classical phase space (Vlasov and Wigner equations). The phase-space approach provides a useful link between the classical and quantum dynamics and is well suited to model effects beyond the mean field approximation (electron-electron and electron-phonon collisions). We will also develop a quantum hydrodynamic model, based on velocity moments of the corresponding Wigner distribution function: this approach should lead to considerable gains in computing time in comparison with simulations based on conventional methods, such as density functional theory (DFT). Finally, the magnetization (spin) dynamics will also be addressed.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
