Anisotropic Kondo Effect in Molybdenum/Carbon Nanotube Array Heterostructures.

The Kondo effect in dilute magnetic alloys is characterized by two key signatures: a resistivity minimum and a logarithmic temperature-dependent contribution to resistivity. Its essential ingredients are localized magnetic moments and itinerant conduction electrons, which are traditionally described by s-d exchange interaction between conduction electrons and localized d-electron moments. Here, we report an anisotropic Kondo effect in molybdenum/carbon nanotube array heterostructures, where partially unzipped CNT edges are formed at the Mo/CNT interface. In this system, the localized magnetic moments originate from p electrons at the partially unzipped CNT edges, while the itinerant conduction electrons are provided by the Mo strip. When the Mo strip is oriented perpendicular to an underneath highly aligned, partially unzipped CNT array, the Kondo effect and negative magnetoresistance (NMR) are observed. In contrast, when the Mo strip is parallel to the unzipped CNT array, the Kondo contribution is suppressed and positive magnetoresistance (PMR) emerges. The Kondo response depends systematically on the relative orientation between the Mo current direction and the aligned CNT array, following a sin2α angular dependence. This anisotropic Kondo effect is distinct from the conventional s-d exchange-induced Kondo effect and can be interpreted within a theoretical model based on effective s-p exchange interactions between Mo conduction electrons and localized carbon p-electron magnetic moments.These findings highlight the potential for carbon-based magnetism and spintronic application.