The delafossite material PdCoO2 received considerable attention due to its highly conducting Pd layers which are embedded between layers of insulating and non-magnetic CoO2. Substituting the non-magnetic Co3+ by magnetic Cr3+ ions leads to antiferromagnetic (AF) order in PdCrO2. Recent results of angle resolved photoemission demonstrate the presence of a Kondo coupling between localised Cr spins and Pd electrons yielding a Kondo-lattice type conductivity in the Pd layers being influenced by the periodic potential due to AF order [1]. A decrease of the Cr content will suppress the Kondo-lattice effects and finally, in the highly diluted limit, the magnetism of the Cr spins may be determined by single-ion Kondo physics.

The focus of this project will be an investigation of these Kondo coupling effects by substituting non-magnetic Co up to a few parts per thousand with magnetic Cr. To this end electron spin resonance (ESR) will be employed for measuring the Cr spin dynamics directly. This should provide valuable information not only on the dynamical Kondo screening of the Cr spins but also on the electronic properties of the conducting Pd layers.

The project will be subdivided as follows:

-  sample characterization (magnetic susceptibility, electrical resistivity)

-  ESR measurements at various microwave frequencies (L-, X-, Q-band) and at temperatures down to 3K

The interpretation of the ESR results will be based on the notion that the Cr spins in the insulating CoO2 layers are well localized and only weakly coupled to the conductive Pd layer. Therefore, this layered system may serve as an ideal model to investigate the Kondo concept, which assumes well localized magnetic moments in a metallic environment.  In contrast, in previous investigations of the Kondo effect in standard metals doped with magnetic ions the spins were often not well localized, making an interpretation within a single-ion Kondo scenario difficult.

[1] V. Sunko et al., arXiv 1809.08972 (2018)

For further details please contact

Jörg Sichelschmidt (joerg.sichelschmidt@cpfs.mpg.de),

Andrew Mackenzie (andy.mackenzie@cpfs.mpg.de)

Go to Editor View