Transient magnetization dynamics of spin-torque oscillator and magnetic dot coupled by magnetic dipolar interaction: Reading of magnetization direction using magnetic resonance

• Published in: Journal of applied physics 2018-01, Vol.123 (4)
• Main Authors: Kanao, Taro, Suto, Hirofumi, Kudo, Kiwamu, Nagasawa, Tazumi, Mizushima, Koichi, Sato, Rie
• Format: Article
• Language: English
• Subjects: Applied physics; Ferromagnetic resonance; Ferromagnetism; Magnetic fields; Magnetic recording; Magnetization; Response time; Spin dynamics; Torque
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.5004632

We study the magnetization dynamics of a spin-torque oscillator (STO) and a magnetic dot coupled by a magnetic dipolar field using micromagnetic simulation with the aim of developing a read method in magnetic recording that uses magnetic resonance. We propose an STO with a perpendicularly magnetized free layer and an in-plane-magnetized fixed layer as a suitable STO for this resonance read method. When the oscillation frequency of the STO is near the ferromagnetic resonance (FMR) frequency of the magnetic dot, the oscillation amplitude of the STO decreases because FMR excited in the magnetic dot causes additional dissipation. To estimate the read rate of the resonance read method, we study the transient magnetization dynamics to the coupled oscillation state from an initial state where the STO is in a free-running state and the magnetic dot is in a stationary stable state. The STO shows transient dynamics within a time scale of 1 ns, which means that the STO can perform resonance reading with a response time within this time scale. This response time is shorter when the separation length between the STO and the magnetic dot is shorter, which indicates that the response speed can become faster by increasing the strength of the interaction between the STO and the magnetic dot. Successive reads are demonstrated by moving the STO over an array of magnetic dots.