Evidence for nanosized magnetic clusters of Ce-ions in the archetypal heavy fermion metal CeB6

Abstract

Fine details of crystal structure of archetypal CeB6 hexaboride with heavy fermions are studied at temperatures 85 and 500 K by precise X-ray diffraction technique. Small static Jahn-Teller distortions of a simple cubic lattice are observed at these temperatures, leading to emergence of (i) dynamic charge stripes along selected directions <110>, <100>, and <111> in the crystals in combination with (ii) vibrationally coupled pairs of Ce ions. Instead of a Currie-Weiss type behavior, the temperature dependence of magnetization M∼(T − TCrand)−0.8 with TCrand∼TQ∼3.3 K was deduced in a wide temperature range 5–800 K for various directions of external magnetic field, which indicates the Griffiths phase formation with nanosized clusters of magnetic ions in CeB6. Moreover, in contrast to the scenario of a single-ion Kondo lattice, when revealing the power-law behavior of the magnetic contribution ρm(T)∼T−0.4 to the resistivity in the range of 8–90 K, we conclude in favor of the regime of weak localization of charge carriers in CeB6. Fourier maps of electron density confirm the conclusion about the nanosized magnetic clusters of Ce ions in this archetypal strongly correlated electron system with unusual magnetic ground state.