Quasi-Ferromagnet Spintronics in Graphene Nanodisk-Lead System

TL;DR

This paper explores the thermodynamical and spintronic properties of zigzag graphene nanodisks, revealing quasi-phase transitions, lead effects described by Kondo physics, and potential applications in various spintronic devices.

Contribution

It introduces a detailed analysis of nanodisk thermodynamics and spintronic functionalities, including lead effects and device proposals, advancing graphene-based spintronics.

Findings

Identification of a quasi-phase transition in nanodisks

Lead attachment modifies thermodynamic properties and enhances ferromagnetism

Proposal of various spintronic devices using nanodisks

Abstract

A zigzag graphene nanodisk can be interpreted as a quantum dot with an internal degree of freedom. It is well described by the infinite-range Heisenberg model. We have investigated its thermodynamical properties. There exists a quasi-phase transition between the quasi-ferromagnet and quasi-paramagnet states, as signaled by a sharp peak in the specific heat and in the susceptability. We have also analyzed how thermodynamical properties are affected when two leads are attached to the nanodisk. It is shown that lead effects are described by the many-spin Kondo Hamiltonian. There appears a new peak in the specific heat, and the multiplicity of the ground state becomes just one half of the system without leads. Another lead effect is to enhance the ferromagnetic order. Being a ferromagnet, a nanodisk can be used as a spin filter. Furthermore, since the relaxation time is finite, it is possible to control the spin of the nanodisk by an external spin current. We then propose a rich variety of spintronic devices made of nanodisks and leads, such as spin memory, spin amplifier, spin valve, spin-field-effect transistor, spin diode and spin logic gates such as spin-XNOR gate and spin-XOR gate. Graphene nanodisks could well be basic components of future nanoelectronic and spintronic devices.