Valence Fluctuations in CeCo2 and Ti-Doped CeCo2

Abstract

We report on the magnetic measurements of polycrystalline samples of CeCo2 and CeCo(2−x)Tix (x = 0.01, 0.02, 0.03, 0.04, and 0.05) which have been synthesized by an arc melting technique. All these compounds crystallize into the face-centered cubic (FCC) structure with the Fd\( \bar{3} \)m space group. The lattice parameter decreases linearly with increasing Ti content from 7.15808(5) A for x = 0 (CeCo2) to 7.15231(7) A for x = 0.05. The magnetic behavior of these compounds has been investigated in the temperature range 5–400 K. The zero field-cooled (ZFC) and field-cooled magnetization (FC) curves show irreversibility below T = 400 K. This result indicates that an inhomogeneous, dynamic magnetic state exists over a wide temperature range. The magnetic susceptibility for both ZFC and FC cases initially decreases with Ti content and then increases with further Ti addition. This behavior is interpreted in terms of band magnetism in the presence of magnetic clusters. This result indicates that the magnetic inhomogeneity of these alloys becomes dominant over a wide temperature range. The observed temperature dependence of the magnetic susceptibility leads us to suggest that these compounds are in a mixed-valence state of the magnetic Ce3+ ions and non-magnetic Ce4+ ions. This fact allows us to successfully interpret the ZFC magnetic susceptibility data with the two-level ionic inter-configuration fluctuations model. We also observe that the magnetic susceptibility increases by the addition of Ti, as evidenced by the enhancement of the formation of magnetic Co clusters due to local disorder. Finally, the magnetic state below the Curie temperatures are discussed based on Griffiths-like behavior.