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Register a new userAnisotropic Transport Properties of CeRu$_2$Al$_{10}$
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We studied the transport properties of CeRu_2Al_10 single crystals. All the transport properties show largely anisotropic behaviors below T_0. Those along the a- and c-axes show similar behaviors, but are different from those along the b-axis. This suggests that the system could be viewed as a two-dimensional system. The results of the thermal conductivity and thermoelectric power could be explained by assuming the singlet ground state below T_0. However, the ground state is not simple but has some kind of structure within a spin gap.
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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.
A Kondo semiconductor CeRu$_2$Al$_{10}$ with an orthorhombic crystal structure shows an unusual antiferromagnetic ordering at rather high temperature $T_0$ of 27.3 K, which is lower than the Kondo temperature $T_{rm K}sim$ 60 K. In optical conductivity [$sigma(omega)$] spectra that directly reflect electronic structure, the $c$-$f$ 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. With increasing $x$ to 0.05 in Ce(Ru$_{1-x}$Rh$_x$)$_2$Al$_{10}$, the $T_0$ decreases slightly from 27.3 K to 24 K, but the direction of the magnetic moment changes from the $c$ axis to the $a$ axis. Thereby, the $c$-$f$ hybridization gap in the $sigma(omega)$ 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 of the magnetic moment direction originates from the decreasing of the $c$-$f$ hybridization intensity. The magnetic ordering temperature $T_0$ is not directly related to the $c$-$f$ hybridization but is related to the charge excitation at 20 meV observed along the $b$ axis.
We studied the physical properties of two Kondo-lattice compounds, CeRu$_2$As$_2$ and CeIr$_2$As$_2$, by a combination of electric transport, magnetic and thermodynamic measurements. They are of ThCr$_2$Si$_2$-type and CaBe$_2$Ge$_2$-type crystalline structures, respectively. CeRu$_2$As$_2$ shows localized long-range antiferromagnetic ordering below $T_N$=4.3 K, with a moderate electronic Sommerfeld coefficient $gamma_0$=35 mJ/mol$cdot$K$^2$. A field-induced metamagnetic transition is observed near 2 T below $T_N$. Magnetic susceptibility measurements on aligned CeRu$_2$As$_2$ powders suggest that it has an easy axis and that the cerium moments align uniaxially along $mathbf{c}$ axis. In contrast, CeIr$_2$As$_2$ is a magnetically nonordered heavy-fermion metal with enhanced $gamma_0$$>$300 mJ/mol$cdot$K$^2$. The initial onset Kondo temperatures of the two compounds are respectively 6 K and 30 K. We discuss the role of the crystal structure to the strength of Kondo coupling. This work provides two new dense Kondo-lattice materials for further investigations on electronic correlation, quantum criticality and heavy-electron effects.
The orthorhombic compound NdFe$_2$Al$_{10}$ has been studied by powder and single-crystal neutron diffraction. Below $T_N$ = 3.9 K, the Nd$^{3+}$ magnetic moments order in a double-$k$ [$mathbf{k}_1 = (0, frac{3}{4}, 0)$, $mathbf{k}_2 = (0, frac{1}{4}, 0)$] collinear magnetic structure, whose unit cell consists of four orthorhombic units in the $b$ direction.The refinements show that this structure consists of (0 1 0) ferromagnetic planes stacked along $b$, in which the moments are oriented parallel to $a$ (the easy anisotropy axis according to bulk magnetization measurements) and nearly equal in magnitude ($approx 1.7-1.9 mu_B$). The alternating 8-plane sequence providing the best agreement to the data turns out to be that which yields the lowest exchange energy if one assumes antiferromagnetic near-neighbor exchange interactions with $J_1 gg J_2, J_3$. With increasing temperature, the single-crystal measurements indicate the suppression of the $mathbf{k}_2$ component at $T = 2.7$ K, supporting the idea that the anomalies previously observed around 2--2.5 K result from a squaring transition. In a magnetic field applied along the $a$ axis, the magnetic Bragg satellites disappear at $H_c = 2.45$ T, in agreement with earlier measurements. Comparisons are made with related magnetic orders occurring in Ce$T_2$Al$_{10}$ ($T$: Ru, Os) and TbFe$_2$Al$_{10}$.
We report the discovery of CMA, a metal with strong magnetic anisotropy and moderate electronic correlations. Magnetization measurements find a Curie-Weiss moment of $0.83,mathrm{mu_B}$/Mn, significantly reduced from the Hunds rule value, and the magnetic entropy obtained from specific heat measurements is correspondingly small, only $approx 9$ % of $R mathrm{ln},2$. These results imply that the Mn magnetism is highly itinerant, a conclusion supported by density functional theory calculations that find strong Mn-Al hybridization. Consistent with the layered nature of the crystal structure, the magnetic susceptibility $chi$ is anisotropic below 20 K, with a maximum ratio of $chi_{[010]}/chi_{[001]}approx 3.5$. A strong power-law divergence $chi(T)sim T^{-1.2}$ below 20 K implies incipient ferromagnetic order, and an Arrott plot analysis of the magnetization suggests a vanishingly low Curie temperature $T_Csim 0$. Our experiments indicate that CMA~is a rare example of a Mn-based weak itinerant magnet that is poised on the verge of ferromagnetic order.
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