MR Element Free Layer with 4f Elements for Spin Transfer Torque

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Solution Overview

Problem

The miniaturization of CPP-GMR elements in hard disk drives leads to increased current density, causing spin transfer torque that suppresses the output of magneto-resistance effect elements, making it difficult to maintain high sensitivity and recording density.

Innovation Solution

A magneto-resistance effect element is designed with a free layer having a multilayer constitution that includes a magnetic body mixed with elements having 4f electrons, such as Nd, Sm, or Gd, which are incorporated into the CoFe alloy, reducing the influence of spin transfer torque and enhancing the damping constant to prevent magnetization inversion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the CPP-GMR element is miniaturized to increase recording density, then the recording density is improved, but the current density increases causing spin transfer torque that suppresses the output

Engineering Contradiction:

Improverecording densityVSAvoidoutput performance

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The invention changes the material composition parameter of the free layer by mixing elements with 4f electrons (Nd, Sm, Gd) into the CoFe alloy. This parameter change increases the damping constant of the free layer, which suppresses magnetization inversion caused by spin transfer torque, thereby maintaining output performance despite miniaturization

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention creates a composite magnetic layer by combining CoFe alloy with elements having 4f electrons (such as Nd, Sm, or Gd). This composite structure leverages the high damping constant of 4f elements to counteract spin transfer torque effects while preserving the magnetic properties needed for GMR operation

Inventive Principle:

Principle #40Composite materials

2Measurement precision

If the current density is increased due to miniaturization, then the sensitivity is improved, but the spin transfer torque increases causing magnetization inversion

Engineering Contradiction:

ImprovesensitivityVSAvoidmagnetization stability

Core Design Contradiction:

Measurement precisionVSStability of the object's composition

Solution Approach 1:

The invention modifies the damping constant parameter of the free layer by incorporating 4f elements into the CoFe alloy composition. This parameter change increases resistance to spin transfer torque, preventing magnetization inversion even at high current densities required for sensitive detection

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention converts the potentially harmful spin transfer torque effect into a beneficial interaction by using the same spin-polarized electrons to exert a stabilizing torque through the high damping constant of 4f elements, preventing magnetization inversion while maintaining the detection function

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This configuration effectively suppresses magnetization inversion and maintains high output performance by ensuring the magnetic body is less affected by spin transfer torque, thereby achieving reliable operation under external magnetic fields.

Implementation Method 1

When the current density is increased, there arises a problem that spin transfer torque is generated to suppress the output of the magneto-resistance effect element

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 2

A CIP-GMR (Current in Plane-Giant Magneto-resistance) element which is a giant magneto-resistance effect element

Methodology Applied

Scientific EffectMagnetoresistance effect:

Implementation Method 3

a pinned layer is formed not into a single-layer constitution of ferromagnetic material but into a three-layer constitution (synthetic pinned layer) consisting of a ferromagnetic layer (inner layer)/a nonmagnetic metal layer (nonmagnetic intermediate layer)/a ferromagnetic layer (outer layer), thereby imparting strong exchange coupling between the two ferromagnetic layers

Methodology Applied

Scientific EffectExchange coupling:

Implementation Method 4

A CIP-GMR (Current in Plane-Giant Magneto-resistance) element which is a giant magneto-resistance effect element

Methodology Applied

Scientific EffectGiant magneto-resistance effect:

Implementation Method 5

a magnetic head that uses a TMR (Tunnel Magneto-resistance) element

Methodology Applied

Scientific EffectTunnel magneto-resistance effect:

Data Source

PatentUS8203808B2Magneto-resistance effect element including free layer having multilayer constitution including magnetic body mixed with element having 4F electrons

Publication Date: 2012.06.19 TDK CORP

AI summary

In an MR element constituted in such a manner that a pinned layer whose magnetization direction is fixed, a nonmagnetic spacer layer, and a free layer whose magnetization direction is changed according to an external magnetic field, are laminated in this order; the free layer has a multilayer constitution including a magnetic body mixed with an element having 4f electrons at a certain ratio. Specifically, the first layer in contact with the spacer layer, the third layer, the fifth layer, and the seventh layer of the free layer are formed by mixing Nd, Sm, Gd, or Tb into CoFe. The second layer and the sixth layer of the free layer are formed by mixing Nd, Sm, Gd, or Tb into NiFe. The third layer of the free layer is Cu. A damping constant of the free layer is greater than 0.018.