Anomalous temperature dependence of the magnetic field induced antiferromagnetic moment in the antiferroquadrupolar ordered state of CeB6

The magnetic field induced antiferromagnetic moment M-AF at low magnetic fields in the antiferro-quadrupolar (AFQ) ordered phase of CeB6 was investigated by elastic neutron diffraction experiments for H parallel to [110]. The peak intensity at the AF magnetic reciprocal point (1/2, 1/2, 1/2) corresponding to M-AF(2) increases with decreasing temperature below the AFQ ordering temperature T-Q, and exhibits a broad maximum at T similar to 3 K and decreases with a further decrease of temperature. This unusual behavior of MF at low fields is explained as a result of the competition between the AF-octupolar and AF-exchange interactions in the O-xy type AFQ ordered state.