Thermagnonic spin-torque oscillator(STO) and sensor utilizing same to detect shifts in the free layer magnetization oscillation frequency

Abstract

A “thermagnonic” spin-torque oscillator (STO) uses heat flow alone to cause the spin-torque (ST) effect and generate the persistent oscillation of the free layer magnetization. In addition to the conventional free and reference layers, the thermagnonic STO also includes a magnetic oxide layer having a fixed in-plane magnetization, a ferromagnetic metallic layer on one surface of the magnetic oxide layer, a nonmagnetic electrically conductive layer between the free layer and the metallic layer, and an electrically resistive heater on the other surface of the magnetic oxide layer. Due to the thermagnonic effect, heat flow from the magnetic oxide layer through the metallic layer, conductive layer and free layer ultimately results in a spin transfer torque (STT) to the free layer. Electrical sense current flowing in the opposite direction as the heat flow is used to monitor the frequency of oscillation of the free layer magnetization.

Description

FIELD OF THE INVENTION[0001]The invention relates generally to a spin-torque oscillator (STO), and more particularly to a magnetic field sensor and sensing system that uses a STO sensor.BACKGROUND OF THE INVENTION[0002]One type of conventional magnetoresistive (MR) sensor used as the read head in magnetic recording disk drives is a “spin-valve” sensor based on the giant magnetoresistance (GMR) effect. A GMR spin-valve sensor has a stack of layers that includes two ferromagnetic layers separated by a nonmagnetic electrically conductive spacer layer, which is typically copper (Cu). One ferromagnetic layer adjacent the spacer layer has its magnetization direction fixed, such as by being pinned by exchange coupling with an adjacent antiferromagnetic layer, and is referred to as the reference layer. The other ferromagnetic layer adjacent the spacer layer has its magnetization direction free to rotate in the presence of an external magnetic field and is referred to as the free layer. With...

AI Technical Summary

Benefits of technology

[0007]The STO according to the present invention is a “thermagnonic” STO that uses heat flow alone to cause the ST effect and generate the persistent oscillation of the free layer magnetization. The thermagnonic STO can also function as an STO magnetic field sensor, such as a magnetic recording disk drive read head. In addition to the conventional free and reference layers, the thermagnonic STO also includes a magnetic oxide layer having a fixed in-plane magnetization, a ferromagnetic metallic layer on one surface of the magnetic oxide layer, a nonmagnetic electrically conductive layer between the free layer and the metallic layer, and an electrically resistive heater on the other surface of the magnetic oxide layer. Due to the thermagnonic effect, heat flow from the magnetic oxide layer through the metallic layer, conductive layer and free layer ultimately results in a spin transfer torque (STT) to the free layer. Electrical sense current flowing in the opposite direction as the heat flow is used to monitor the frequency of oscillation of the free layer magnetization. Because the sense current electron flow is in the same direction as the heat flow, the electron current does not exert appreciable spin-torque on the free layer. In this way the flow of heat provides a means of generating ST on the free layer that is independent of the charge current flow used to sense the oscillation. This allows for a large charge current to be applied which results in large STO power, much larger than if the spin current associated with charge current flow alone were used to generate oscillations.

Problems solved by technology

This allows for a large charge current to be applied which results in large STO power, much larger than if the spin current associated with charge current flow alone were used to generate oscillations.

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