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Spin-torque oscillators (STOs) are unique spintronic devices in which spin current induces the precession of magnetization in the oscillation layer. In this study, we demonstrate coupled out-of-plane oscillation between two oscillation layers within an STO. The coupled oscillation state is observed in the magnetoresistance spectra as well as its degradation due to the mixing of the free oscillation state depending on the bias current. These behaviors are analytically described and numerically reproduced based on the Landau–Lifshitz–Gilbert equation. Since the STO is fabricated in the write head of a hard disk drive, the coupled oscillation state and the subsequent microwave magnetic field are applicable for microwave-assisted magnetic recording for high-density recording. [ABSTRACT FROM AUTHOR]

A free bubble reaching the liquid surface usually bursts and then forms a liquid jet with drops ejected. While bubble-mediated jetting is a topic widely studied, few investigations deal with the jet produced by a growing bubble. Here, we report and characterize a novel phenomenon, named periodic bubbling-bursting, that can develop when a continuous stream of gas penetrates through a thin liquid layer. This behavior is complex with a characteristic frequency and can be divided into three stages from bubbling to cavity collapse and jetting. We show that increasing the liquid layer thickness and gas velocity leads to a larger bubble. However, the effect is strongly coupled with the orifice diameter and a scaling law of the bubble rupture radius is derived. Subsequently, we demonstrate that the collapsing cavities exhibit shape similarity and deduce the dependence of pinch-off height and opening angle of the conical cavity on the bubble rupture radius and liquid layer thickness. This enables us to disentangle three different neck-pinching mechanisms at play in pinch-off. Accordingly, gravity shapes the cavity and participates in the capillary wave selection that strongly modulates the jet formation. With increasing layer thickness, the jet first becomes fat and small and then ends up thinner and higher, detaching more and smaller droplets. We present a simple scaling law for the jet velocity which involves the liquid layer thickness to the power 1/2. Finally, a phase diagram for jet breakup and no breakup is built with respect to the initial Weber and Bond numbers. [ABSTRACT FROM AUTHOR]

Spin-transfer-induced magnetic excitation in large magnetic field applied perpendicular to the thin film junction surface reveals both a current threshold Ic and a voltage threshold. The current threshold follows the Slonczewski-type of magnetic field dependence [J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996)]. The voltage step at Ic is ΔV which appears to scale with the applied field with a prefactor of the order of 2μB/e, suggesting a threshold to magnetic excitation. Furthermore, experimentally it is observed that ΔV≈IcδR, where δR is the magnetoreistance between the parallel and the antiparallel states. This apparent coincidence can be unified when one includes the effect of spin-pumping-related nonlocal damping. The spin-pump damping relates magnetic instability threshold Ic to δR, producing (dIc /dH)δR that is about 2μB/e, explaining the origin of the coincidence. [ABSTRACT FROM AUTHOR]