47 research outputs found
Temperature-Dependent Cycloidal Magnetic Structure in GdRuAl Studied by Resonant X-ray Diffraction
We have performed resonant X-ray diffraction experiments on the
antiferromagnet GdRuAl and have clarified that the magnetic
structure in the ordered state is cycloidal with the moments lying in the
plane and propagating along the axis. The propagation vector shows a
similar temperature dependence to the magnetic order parameter, which can be
interpreted as being associated with the gap opening in the conduction band and
the resultant change in the magnetic exchange interaction. Although the
state of Gd is almost isotropic, the moments show slight preferential ordering
along the axis. The axis component in the cycloid develops with
decreasing temperature through a tiny transition in the ordered phase. We also
show that the scattering involves the - process, which is
forbidden in normal - resonance of magnetic dipole origin. We discuss
the possibility of the - resonance originating from a toroidal moment
due to the lack of inversion symmetry at the Gd site. The spin-flop transition
in a magnetic field is also described in detail.Comment: 8 pages, 11 figures, accepted for publication in J. Phys. Soc. Jp
Effect of Nd substitution on the magnetic order in Ce_xNd_{1-x}B_6 solid solutions
Neutron powder diffraction measurements have been performed on
Ce_xNd_{1-x}B_6 (x = 0.5, 0.6, 0.7, and 0.8) solid solutions to determine the
type of magnetic order occurring in these compounds as a result of the
interplay between magnetic dipole exchange and antiferroquadrupolar
interactions. In the Ce-rich range, the sequence of two magnetic phases, with
an incommensurate order [k = (1/4 -\delta, 1/4 -\delta, 1/2)] forming below T N
followed by a lock-in--type transition at lower temperature, is quite similar
to that reported earlier for Ce_xPr_{1-x} B_6. For x = 0.5, on the other hand,
the same antiferromagnetic order as in pure NdB6 first occurs at TN, then
coexists with an incommensurate component below the lower transition
temperature. These results are in good agreement with previous resistivity
measurements and support the idea that Ce and Nd magnetic moments in this
system can be relatively decoupled.Comment: 7 page
Magnetic-Field-Induced 4f-Octupole in CeB6 Probed by Resonant X-ray Diffraction
CeB6, a typical Gamma_8-quartet system, exhibits a mysterious
antiferroquadrupolar ordered phase in magnetic fields, which is considered as
originating from the T_{xyz}-type magnetic octupole moment induced by the
field. By resonant x-ray diffraction in magnetic fields, we have verified that
the T_{xyz}-type octupole is indeed induced in the 4f-orbital of Ce with a
propagation vector (1/2, 1/2, 1/2), thereby supporting the theory. We observed
an asymmetric field dependence of the intensity for an electric quadrupole (E2)
resonance when the field was reversed, and extracted a field dependence of the
octupole by utilizing the interference with an electric dipole (E1) resonance.
The result is in good agreement with that of the NMR-line splitting, which
reflects the transferred hyperfine field at the Boron nucleus from the
anisotropic spin distribution of Ce with an O_{xy}-type quadrupole. The
field-reversal method used in the present study opens up the possibility of
being widely applied to other multipole ordering systems such as NpO2,
Ce_{x}La_{1-x}B_{6}, SmRu_{4}P_{12}, and so on.Comment: 5 pages, 4 figures, submitte
High-field magnetization and magnetic phase transition in CeOs2Al10
We have studied the magnetization of CeOs2Al10 in high magnetic fields up to
55 T for H // a and constructed the magnetic phase diagram for H // a. The
magnetization curve shows a concave H dependence below T_max \sim40 K which is
higher than the transition temperature T_0 \sim29 K. The magnetic
susceptibility along the a-axis shows a smooth and continuous decrease down to
\sim20 K below T_max \sim40 K without showing an anomaly at T_0. From these two
results, a Kondo singlet is formed below T_max and coexists with the antiferro
magnetic order below T_0. We also propose that the larger suppression of the
spin degrees of freedom along the a-axis than along the c-axis below T_max is
associated with the origin of the antiferro magnetic component.Comment: 4 pages, 4 figures, to appear in Phys. Rev. B, Rapid Commu