Tuning spin one channel to exotic orbital two-channel Kondo effect in ferrimagnetic composites of LaNiO₃ and CoFe₂O₄

We report the tuning from spin one channel to orbital two-channel Kondo (2CK) effect by varying CoFe₂O₄ (CFO) content in the composites with LaNiO₃ (LNO) along with the presence of ferrimagnetism. Although there is no signature of resistivity upturn in the case of pure LNO, all the composites exhibit a distinct upturn in the temperature range of 30-80 K. For composites with lower percentage of CFO (10%), the electron spin plays the key role in the emergence of resistivity upturn which is affected by external magnetic field. On the other hand, when the CFO content is increased (15%), the upturn shows strong robustness against high magnetic field (14 T) and a crossover in temperature variation from to T ^1/2 at the Kondo temperature, indicating the appearance of orbital 2CK effect. The orbital 2CK effect originates due to the scattering of conduction electrons from the structural two-level systems which is created at the interfaces between the two phases (LNO and CFO) of different crystal structures as well as inside the crystal planes. The specific heat data at low temperature (40 K), deviates from the usual linear temperature variation of the electronic contribution. With higher CFO content it shows more deviation which also indicates the increasing amount of two-level system. A negative magnetoresistance (MR) is observed at low temperature (<30 K) for composites containing both lower (10%) and higher percentage (15%) of CFO. We have analyzed the negative MR using Khosla and Fisher semi-empirical model based on spin dependent scattering of conduction electrons from localized spins.