Magnetoresistance: Measurement, Types, And Applications

Introduction

Magnetoresistance is defined as the change in the electrical resistance of a material when an external magnetic field is applied. This property is important for various technological applications, for example, magnetic sensors, data storage devices and automotive systems.

Types of Magnetoresistance

Ordinary Magnetoresistance

Ordinary magnetoresistance occurs in non-magnetic materials and usually varies linearly with the applied magnetic field. It is caused by the classical motion of charge carriers in the presence of a magnetic field.

Giant Magnetoresistance (GMR)

Giant magnetoresistance is observed in multilayer structures that consist of alternating ferromagnetic and non-magnetic conductive layers. GMR has allowed the development of hard disk drives with high storage capacity, thereby reducing the size of read/write heads and increasing storage density.

Colossal Magnetoresistance (CMR)

Colossal magnetoresistance is characterised by an exceptionally large change in resistance under a magnetic field, which is often observed in manganese oxides. CMR materials are of interest for future electronic and spintronic devices.

Bismuth and its Magnetoresistive Properties

Bismuth is a semimetal known for its high magnetoresistance. Its unique electronic structure and low charge carrier density make it a suitable candidate for investigating magnetoresistive phenomena and for developing sensitive magnetic field detectors.

Measuring Magnetoresistance

Experimental Setup

In measuring magnetoresistance, a magnetic field is applied to a material and the resulting change in electrical resistance is measured. This process typically requires a stable magnetic field source, such as a superconducting magnet, and precise electrical measurement instruments, for example, a four-point probe.

Measurement Techniques

• Longitudinal Magnetoresistance: Measures the resistance along the direction of the applied magnetic field.
• Transverse Magnetoresistance: Measures the resistance perpendicular to the magnetic field and provides information regarding the Hall effect of the material.
• Angular-Dependent Magnetoresistance: Varies the angle between the current and the magnetic field to investigate anisotropic properties.

Data Analysis

The change in resistance is frequently plotted against the magnetic field strength to analyse the magnetoresistive behaviour of the material. Key parameters, such as the magnetoresistance ratio and the saturation field, are extracted to characterise the performance of the material.

Further information can be found at Stanford Advanced Materials (SAM).

Applications of Magnetoresistance

Data Storage

GMR and CMR are used in the development of hard disk drives that offer high storage capacities. Smaller and more efficient read/write heads contribute to increased storage density.

Magnetic Sensors

Magnetoresistive sensors are utilised in various applications, for example in automotive systems to monitor wheel speed, as position sensors in robotics, and as read heads in magnetic storage devices.

Spintronics

Magnetoresistance is employed in spintronic devices. In these devices, the spin of electrons is used alongside their charge for information processing, thereby yielding faster and more efficient electronic systems.

Frequently Asked Questions

What is magnetoresistance used for? Magnetoresistance is used in data storage devices, magnetic sensors and spintronic applications.

How does giant magnetoresistance differ from ordinary magnetoresistance? Giant magnetoresistance involves a substantially larger change in resistance due to multilayer structures, whereas ordinary magnetoresistance occurs in single non-magnetic materials with smaller resistance changes.

Why is bismuth significant for magnetoresistance studies? Bismuth has a unique electronic structure with a low charge carrier density. This results in pronounced magnetoresistive effects that are valuable for both research and applications.

Which devices are required to measure magnetoresistance? A stable magnetic field source, such as a superconducting magnet, and precise electrical measurement instruments, for example a four-point probe, are required.

Can magnetoresistance be observed in all materials? No. Magnetoresistance is generally observed in materials with specific electronic properties, such as high mobility or particular band structures, and is more pronounced in materials like bismuth, multilayer ferromagnets and manganese oxides.