Y. Tabata

Non-fermi-liquid scaling in Ce(Ru0.5Rh)2Si2.

We study the temperature and field dependence of the magnetic and transport properties of the non-Fermi-liquid (NFL) compound Ce(Ru0.5Rh0.5)2Si2. For fields H less, similar0.1 T the results suggest that the observed NFL behavior is disorder driven. For higher fields, however, magnetic and transport properties are dominated by the coupling of the conduction electrons to critical spin fluctuations. The temperature dependence of the susceptibility as well as the scaling properties of the magnetoresistance are in very good agreement with the predictions of recent dynamical mean-field theories of Kondo alloys close to a spin-glass quantum critical point.

Spin density wave and heavy electrons in Ce(Ru1−xRhx)2Si2 and Ce1−xLaxRu2Si2

Abstract We study the magnetic properties of heavy electrons in Ce(Ru 1− x Rh x ) 2 Si 2 and Ce 1− x La x Ru 2 Si 2 associated with ordering of a spin density wave. One of the short-range orders in CeRu 2 Si 2 is stabilized as a long-range order. Anisotropic gap opening occurs in partial Fermi surfaces below the ordering temperature T N and the rest of the Fermi surfaces contribute to heavy-fermion properties.

Crossover between “localized” and “itinerant” antiferromagnetic states in Ce(Ru0.9Rh0.1)2(Si1−yGey)2 driven by chemical pressure

We have investigated the magnetization process of the pseudobinary Kondo-lattice system Ce(Ru0.9Rh0.1)2–(Si1−yGey)2. The base material Ce(Ru0.9Rh0.1)2Si2, which has a spin density wave (SDW) phase below , shows two-step metamagnetic behavior at Hc and HM; the SDW-Fermi liquid (FL) transition occurs at Hc, and FL state becomes unstable and localized spin character recovers at HM. By substituting Ge for Si, HM reduces very rapidly and disappears for y>0.08, where the magnetization curve is quite similar to those of localized Ising spin antiferromagnets (AF). This observation is interpreted as a manifestation of crossover of the character of the AF state from “itinerant” to “localized” induced by the negative chemical pressure.

Non-Fermi-liquid-like behavior in Ce(Ru1− xRhx)2Si2 (0.3 ⩽ × ⩽ 0.5)

Abstract We have studied the magnetic properties of the mixed-compound system Ce(Ru 1− x Rh x ) 2 Si 2 (0.3 ⩽ × ⩽ 0.5) by means of specific heat and magnetization measurements with single-crystalline samples. In the intermediate concentration range,0.3 ⩽ × ⩽ 0.5, we observed non-Fermi-liquid-like behavior in the temperature dependence of the magnetic specific heat. We compare the temperature dependence of the susceptibilities with the results of the calculation by the crystalline electric field model. Below about 100 K the susceptibilities deviate downward from the calculation; this means that the Kondo effect exists in the intermediate concentration range.

Anisotropy dependence of anomalous Hall effect in canonical spin glass alloys

The influence of the Dzyaloshinsky–Moriya (DM) anisotropy on the extraordinary Hall coefficient , where ρex is the extraordinary Hall resistivity and M is the magnetization, is investigated in canonical spin-glass (SG) alloys. The strength of the DM anisotropy in the alloys is changed systematically by doping with a third impurity that is non-magnetic. The Hall resistivity ρH, the magnetization M and the resistivity ρ were measured in the series of (Ag1−xAux)0.9Mn0.1 alloys with x = 0, 0.007, 0.03, and 0.05. The difference ΔRs between the values of zero-field-cooled and field-cooled Rs, below the SG transition temperature, clearly increased with the amount of Au impurities. The dependence of the chirality contribution to Rs on the DM anisotropy is discussed in relation to the theoretical work for the chirality-driven anomalous Hall effect in the weak coupling regime.

Spin correlation in kagomé ice state: Neutron scattering study of the dipolar spin ice Dy2Ti2O7 under magnetic field along [1 1 1]

Abstract We have investigated the kagome ice state in the frustrated pyrochlore oxide Dy 2 Ti 2 O 7 under magnetic field along a [1xa01xa01] axis. Spin correlations have been measured by neutron scattering and analyzed by Monte Carlo simulation. The kagome ice state, which has a non-vanishing residual entropy well established for the nearest-neighbor spin ice model by the exact solution, has been proved to be realized in the dipolar-interacting spin ice Dy 2 Ti 2 O 7 by observing the characteristic spin correlations. The simulation shows that the long-range interaction gives rise to only weak lifting of the ground state degeneracy and that the system freezes within the degenerate kagome ice manifold .

Instability of RKKY-type long-range order in Kondo-lattice compound Ce(Ru0.9Rh0.1)2(Si1−yGey)2 as studied by neutron diffraction

Neutron diffraction experiments have been made to study the response of the magnetic order of the heavy-fermion compound Ce(Ru0.9Rh0.1)2(Si1−yGey)2 to hydrostatic pressure and to the chemical-pressure. With changing the Ge concentration, both the magnitude of the magnetic moment and the value of the wave number shows rapid change at around y=0.08. The third harmonic component of the modulation of the y=0.2 compound clearly exhibits localized-electron nature at low temperature.

Low-temperature specific heat of Ce(Ru1-xRhx)2Si2 and (Ce1-xLax)Ru2Si2

Abstract We have measured the specific heat by a thermal relaxation method on about 10 mg single crystalline samples of Ce(Ru1-xRhx)2Si2 (x=0.1, 0.15, 0.3 and 0.4) and (Ce0.87La0.13)Ru2Si2 from 1.5 K to 20 K. Ce(Ru1-xRhx)2Si2 with x=0.1 and 0.15 and (Ce0.87La0.13)Ru2Si2 show magnetic phase transition and the temperature dependence of the magnetic specific heat, Cmag, obeys approximately the power law Cmag = ATn below the ordering temperatures with n=1.4 for both the Ce(Ru1-xRhx)2Si2 and with n=1.1 for (Ce1-xLax)Ru2Si2. The estimated electronic specific heat coefficient γ for x=0.1 is nearly of the same value (= 360 mJ/mol K2) as for CeRu2Si2. The Cmag/T for both x=0.3 and 0.4 diverges logarithmically for T → 0, which suggests the so-called non-Fermi liquid behavior.

Observation of field-induced magnetic and structural transitions in an antiferromagnet by means of synchrotron x-rays

In the first experiment of its kind, we have used x-ray diffraction to study magnetic and charge properties of an antiferromagnet as a function of an applied magnetic field H. The intensity of hard x-rays diffracted at the space-group-forbidden reflection (3, 0, 0) of MnF2 with H parallel to the easy axis at H = Hc /√2 shows evidence of a spin-flop transition associated with the surface magnetization, and at Hc = 9.3 T a spin-flop transition in the bulk. Above Hc we found intensity much larger than that predicted for purely magnetic scattering. We attribute the unexpected intensity to charge scattering created by a field-induced structural phase transition.

Synchrotron X-ray Diffraction Studies of the Incommensurate Phase of a Spin–Peierls System CuGeO3 in Strong Magnetic Fields

Synchrotron X-ray diffraction measurements on a spin–Peierls material CuGeO 3 in applied magnetic fields, H , up to 15 T are made. We find that the temperature, T , dependence of the incommensurate Bragg peak at a lower H is quite different from that at a higherxa0 H . At sufficiently high fields, we find that the lattice incommensurability, δ l , is almost independent of T , while at H slightly above the critical field = 12.25 T for the commensurate to incommensurate transition, δ l decreases with increasing T . We interpret that this finding is due to a stabilization of the incommensurate state by a strong magnetic field which suppresses thermal fluctuations.