No abstract

In an array of spin-torque nano-oscillators (STNOs) that combine a perpendicular polarized fixed layer with strong in-plane anisotropy in the free layers, magnetic dipolar interactions can effectively phase-lock the array, thus further enhancing the power of the output microwave signals. We perform a qualitative analysis of the synchronization of an array based on the Landau-Lifshitz-Gilbert equation, with a spin-transfer torque that assumes strong in-plane anisotropy. Finally, we present the numerical results for four coupled STNOs to provide further evidence for the proposed theory.

This paper reviews the progress made over the last few years in understanding the development of perpendicular magnetic tunneling junctions (pMTJs). The material systems for making pMTJs, including rare-earth/transition metal alloys, L10-ordered (Co, Fe)–Pt alloys, Co/(Pd, Pt) multilayers, and CoFeB–MgO crystallized structures, are briefly introduced. The fabrication processes of the MTJ devices are focused on, consisting of open-trench, etch-back and self-aligned techniques. The authors also propose a spin-torque nano-oscillator based on pMTJ, for application in GHz range telecommunications.

Fabrication and magnetization characteristics of permalloy nanotube arrays that are in 100-nm-scale have been demonstrated. Permalloy nanotube array is made by using a standard electron-beam lithography combining with an ion-beam milling process. Geometric parameters of individual permalloy nanotube are fixed to be 300/20 nm for outer diameter/wall thickness, and the heights are varied from 180 to 600 nm. Height dependent magnetization reversal behaviors are investigated by using longitudinal magneto-optical Kerr effect with the external field applied perpendicular to the tubular axis. Micromagnetic simulations are performed to scrutinize the micromagnetization configurations. Up to two pairs of head-to-head and tail-to-tail domain walls on both tubular ends and vortex structure motion on the sidewall are identified during the magnetization reversal.

This study reports an alternative method for measuring the magnetoresistance of unpatterned magnetic tunnel junctions similar to the current-in-plane tunneling (CIPT) method. Instead of using microprobes, a series of point contacts with different spacings are coated on the top surface of the junctions and R-H loops at various spacings are then measured by the usual four-point probe method. The values of magnetoresistance and resistance-area products can be obtained by fitting the measured data to the CIPT theoretical model. The test results of two types of junctions were highly similar to those obtained from standard CIPT tools. The proposed method may help to accelerate the process for evaluating the quality of magnetic tunnel junctions when commercial CIPT tools are not accessible.