First-principles calculation of monitoring spin states of small magnetic nanostructures with IR spectrum of CO

Abstract

Abstract. A fully ab initio controlled ultrafast magnetooptical switching mechanism in small magnetic clusters is achieved through exploiting spin-orbit-coupling enabled Λ processes. The idea is that in the magnetic molecules a fast transition between two almost degenerate states with different spins can be triggered by a laser pulse, which leads to an electron excitation from one of the degenerate states to a highly spin-mixed state and a deexcitation to the state of opposite spin. In this paper a CO molecule is attached to one magnetic center of the clusters, which serves as an experimental marker to map the laser-induced spin manipulation to the IR spectrum of CO. The predicted spin-state-dependent CO frequencies can facilitate experimental monitoring of the processes. We show that spin flip in magnetic atoms can be achieved in structurally optimized magnetic clusters in a subpicosecond regime with linearly polarized light. IntroductionIn recent years there has been a continuous strain to increase the storage capacity as well as to minimize as much as possible the time needed to record data on magnetic materials. However, the tremendous increase in the storage density and read-write speed in magnetic storage media is reaching its physical limits. Manipulation of the spin degree of freedom is attracting more and more attention due to its potential to increase the information density and speed in computational device applications. Many light-driven scenarios and mechanisms of demagnetization have already been proposed [1,2,3], and it has been demonstrated that subpicosecond magnetic switching can be achieved by exploiting the ultrafast electron-photon interaction [4,5]. Laser manipulation has been well understood in atomic and molecular systems, which stimulates the implementation of these mechanisms in practical device applications.At the same time, monitoring spin manipulation is another important and necessary aspect in device realization. Although it is possible to theoretically predict the spin state of matter, it is still one of the significant problems that experiment will encounter. Here a possible solution to this problem is proposed. We use a CO molecule as an experimental marker attached to the investigated magnetic clusters. The CO marker changes the electronic structure of the magnetic cluster only minimally, however it lowers its symmetry. If certain magnetic states of the cluster correspond to specific CO vibrational frequencies, experiment can reveal the spin state indirectly from the infrared (IR) spectrum of CO, which is a common and reliable technique in experiment.