Substitution effect on the magnetic and transport properties of CeNi0.8−xMnxBi2

Abstract

We report the results of Mn substitution for Ni in CeNi0.8Bi2 (i.e., CeNi0.8−xMnxBi2). All the samples have an antiferromagnetic ordered state below TN = 5.0 K due to localized 4f-magnetic moment on the Ce ions. Besides this antiferromagnetic ordering caused by Ce, the magnetic and transport properties are abruptly changed with increasing Mn contents at the boundary composition of x = 0.4. The magnetic state is changed into a ferromagnetic state around 200 K for x > 0.4, where the electrical resistivity is strongly suppressed to become simple metallic. These results of ferromagnetism and metallicity can be explained by the double exchange mechanism, rather than the simple picture of Doniach phase diagram. The mixed valence states of Ni and Mn ions are confirmed by X-ray photoelectron spectroscopy. For x ≤ 0.4, the initial Ni3+ state gradually changes to the Ni2+ state with increasing x up to 0.4. On further increase of x > 0.4, the Ni2+ state is replaced by the Mn2+ state, which gradually changes to the final Mn3+ state. We also present an inelastic neutron scattering (INS) measurements on CeNi0.8Bi2 (i.e., x = 0) between 1.2 and 12 K. The high energy INS study reveals the presence of two well-defined crystal electric field (CEF) excitations near 9 meV and 19 meV at 1.2 K and 6 K, while the low energy INS study reveals the presence of quasielastic scattering above 4 K. We will discuss our INS results of CeNi0.8Bi2 based on the CEF model.