DMRG Analysis of Magnetic Order in the Zigzag Edges of Hexagonal CrN Nanoribbons

TL;DR

This study combines advanced computational methods to analyze magnetic order and spin transport in zigzag CrN nanoribbons, revealing their potential as spin filters but highlighting limitations for room temperature applications.

Contribution

It introduces a comprehensive approach combining DFT, DMRG, and Boltzmann transport theory to understand magnetic and electronic properties of CrN nanoribbons.

Findings

Zigzag edges are energetically favorable over armchair edges.

Zigzag CrN nanoribbons exhibit half-metallicity similar to 2D monolayers.

Spin correlation length drops sharply with temperature, limiting room temperature spintronic use.

Abstract

We investigate the finite temperature magnetic order at the edges of hexagonal CrN nanoribbons by using the density-functional theory combined with the density-matrix renormalization group method. Moreover, the spin-dependent transport in nanoribbons is calculated within the semi-classical Boltzmann transport theory. We find out that the zigzag edges have lower energy with respect to armchair edges. The zigzag edge of CrN nanoribbon shows half metallic electronic character which is the same as for the 2D monolayer. The localized electronic states on the zigzag edges reduce the electronic band gap energy for spin down electrons. The ab-initio electronic results are mapped into an effective 1D Heisenberg spin model up to the next nearest neighbor exchange interaction term. For zigzag ribbons, the nearest neighbor and next nearest neighbor magnetic exchange are around $10$ to $12$, and $-2$ to $0$~meV/Cr atom, respectively. The finite spin correlation length in 1D nanoribbons drops sharply to zero with temperature. The absence of long range spin correlations at the edges is a practical drawback for future room temperature 2D spintronic devices. The maximally localized Wannier functions are used for band interpolation and spin-dependent transport calculations by using the semi-classical Boltzmann equation. We show that zigzag edges of CrN are perfect spin filter under both electron and hole doping.