The effects of a weak microwave field in the magnetization dynamics driven by spin-transfer-torque in spin valves with perpendicular materials have been systematically studied by means of full micromagnetic simulations. In the system we studied, depending on the working point (bias field and current) in the dynamical stability diagram, we observe either resonant switching or injection locking. The resonant switching, observed in the switching region, occurs when the field frequency is approaching the frequency of the main preswitching mode giving rise to an asymmetric power distribution of that mode in the sectional area of the free layer. At the resonant frequency, the switching time is weakly dependent on the relative phase between the instant when the current pulse is applied and the microwave field. The injection locking, observed in the dynamical region, is characterized by the following properties: (i) a locking bandwidth which is linearly dependent on the force locking and (ii) a locking for integer harmonics of the self-oscillation frequency. We compare our numerical results with analytical theory for nonautonomous nonlinear system obtaining a good agreement in the current region where the oscillation frequency and output power are characterized by a linear relationship.
|Autori interni:||CARPENTIERI, Mario|
|Titolo:||Spin-transfer-torque resonant switching and injection locking in the presence of a weak external microwave field for spin valves with perpendicular materials|
|Rivista:||PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS|
|Data di pubblicazione:||2010|
|Digital Object Identifier (DOI):||10.1103/PhysRevB.82.094434|
|Appare nelle tipologie:||1.1 Articolo in rivista|