Nabil M. Al-Aqtash

We report the theoretical study of the light-induced switching of magnetization in core–shell nanoparticles. The core of the nanoparticle is made of iron (Fe) coated with the shell of azobenzene. Azobenzene is a photochromic material with reversible trans–cis photoisomerization upon irradiation by UV and visible light. The magnetization of nanoparticles can be reversibly switched using specific wavelengths of light. Using an ab initio parameterization of magnetic interactions we performed Monte Carlo simulations of the magnetization of the core–shell nanoparticle as a function of temperature. The results show that Fe nanoparticle magnetization can be switched by at least 50% because of the photoisomerization of azobenzene at room temperature. Ab initio calculations show that the exchange interaction in Fe dimer is ferromagnetic (FM), and shows a strong modification of exchange interaction parameters by 40% because of the trans–cis photoisomerization of azobenzene. An infinite planar Fe monolayer mimicking the surface of nanoparticle shows a strong modification of exchange interaction parameters (up to 50%) in the monolayer due to trans–cis photoisomerization. The local magnetic moments of Fe sheet increase by only 0.5% due to photoisomerization.

Zigzag graphene nanoribbons (ZGNRs) are antiferromagnetic in the ground state with zero net magnetization due to the compensation of contributions from opposite edges. Uniform deformations (both shear and axial) do not produce magnetization due to symmetry restrictions. However, we report the results of first-principles calculations that predict the induction of spin density waves (SDWs) in ZGNRs under non-uniform periodic strain. Using the density functional theory (DFT) method, we show that a sinusoidal magnetization variation along the axis of the ribbon occurs under a sinusoidal transversal shear strain. SDWs appear due to the presence of a strain gradient that induced asymmetry of magnetization on opposite edges of ZGNRs which do not compensate each other. The amplitude of SDWs is estimated at ∼0.066μ_B when deformations transverse to the ZGNR axis have a sinusoidal profile with a period of 88.6 Å and an amplitude of 1 Å. Our study suggests that the periodic lattice deformations strongly affect the magnetic structure of ZGNRs in the case of acoustic phonons or mechanical waves.