Spin wave free spectrum and magnetic field gradient of nanopatterned planes of ferromagnetic cobalt nanoparticles: key properties for magnetic resonance based quantum computing

TL;DR

This study investigates the magnetic properties of nanopatterned cobalt nanoparticle sheets, demonstrating their potential for creating strong magnetic field gradients for quantum computing, while addressing spin decoherence issues.

Contribution

It provides experimental and theoretical insights into the magnetic behavior of cobalt nanoparticle sheets and proposes methods to suppress spin decoherence for quantum computing applications.

Findings

Nanoparticle sheets are modeled as 2D ferromagnetic layers with reduced saturation magnetization.

Superparamagnetic behavior observed above 210 K, ferromagnetic below.

Strong magnetic field gradients (~0.1 G/nm) can be generated by nanostripes for quantum computing.

Abstract

We present a study by ferromagnetic resonance at microwave Q band of two sheets of cobalt nanoparticles obtained by annealing SiO2 layers implanted with cobalt ions. This ex- perimental study is performed as a function of the applied magnetic field orientation, tempera- ture, and dose of implanted cobalt ions. We demonstrate that each of those magnetic sheet of cobalt nanoparticles can be well modelled by a nearly two dimensional ferromagnetic sheet hav- ing a reduced effective saturation magnetization, compared to a regular thin film of cobalt. The nanoparticles are found superparamagnetic above around 210 K and ferromagnetic below this blocking temperature. Magnetostatic calculations show that a strong magnetic field gradient of around 0.1 G/nm could be produced by a ferromagnetic nanostripe patterned in such magnetic sheet of cobalt nanoparticles. Such a strong magnetic field gradient combined with electron para- magnetic resonance may be relevant for implementing an intermediate scale quantum computer based on arrays of coupled electron spins, as previously reported (Eur. Phys. J. B (2014) 87, 183). However, this new approach only works if no additional spin decoherence is introduced by the spin waves exitations of the ferromagnetic nanostructure. We thus suggest theoretically some possible magnetic anisotropy engineering of cobalt nanoparticles that could allow to suppress the spin qubit decoherence induced by the unwanted collective excitation of their spins.