Giant magnetoresistance

Giant Magnetoresistance in Magnetic Multilayered Systems The giant magnetoresistance effect is the change of electric conductivity in a system of metallic layers when an external magnetic field changes the magnetization of the ferromagnetic layers relative to each other.

The GMR read head "flys" over the hard disk and senses the magnetic field made by an array of tiny magnetic domains arranged in a circular pattern.

The drawing shows two ferromagnetic layers separated by a nonmagnetic layer. This discovery triggered an extensive research activity in this field in order to understand the underlying physical phenomenon as well as to exploit its technological potential. BoxBielefeld, Germany; ed.

The value of the stored bits can be encoded via the magnetization direction in the sensor layer; it is read by measuring the resistance of the structure. Thus, the potential of magnetoresistive technology seems to be far from being exhausted.

Such a sensor has an asymmetric hysteresis loop owing to the presence of the magnetically hard, fixed layer.


Three phases are anticipated for spintronics: A cell of magnetoresistive random-access memory MRAM has a structure similar to the spin-valve sensor.

Changing the direction of the external Giant magnetoresistance field deflects the magnetization in the sensing layer. When the field tends to align the magnetizations in the sensing and fixed layers, the electrical resistance of the sensor decreases, and vice versa.

Antiferromagnetic Pinning layer, Protective layer. Electrons act like tiny magnets. Ellipses with arrows denote the magnetic field lines around the row and column lines when electric current flows through them. Bunches of oriented electrons already have been shown to preserve their orientation as they move through a wire over short distances, and this effect could become the basis of future computer processing See BBC article in Links.

Thereafter, we will have a look at different systems in which GMR can occur, with emphasis on the application-relevant side. The major problem in spin valve structures is the interface scattering of spins between magnetic and nonmagnetic layers. If the value of the field exceeds some critical value, the latter changes its direction.

The orientation of the magnetization in the ferromagnetic layers strongly influences the resistance of the system. The effect size is defined as: Such devices were reported in and may be used as rectifiers with a linear frequency response. To read the direction of the magnetic field above the domain wall, the magnetization direction is fixed normal to the surface in the antiferromagnetic layer and parallel to the surface in the sensing layer.

These conductors are called lines of rows and columns.

Giant Magnetoresistance: Basic Concepts, Microstructure, Magnetic Interactions and Applications

By separating two ferromagnetic layers with a thin nonmagnetic layer, Gruenberg observed that with no applied magnetic field, the magnetic fields in the two layers were opposite. In this review, we intend to provide an overview of different aspects of the GMR effect.

To fabricate a clean defect-free interface, where there is no scattering, is a great technological challenge. Because the GMR effect is so much stronger than AMR, the domains can be smaller and much more information can be packed onto the disk. A spintronics-based computer would store information in the spins of electrons rather in charges or voltages and process information through interaction among the oriented spins and magnetic domains.

In thin metallic film systems, they observed that the magnetization of adjacent ferromagnetic films, separated by a thin Giant magnetoresistance interlayer, spontaneously align parallel or antiparallel, depending on the thickness of the interlayer.

GMR devices spin valves basically consist of artificial thin film materials of alternate ferromagnetic and nonmagnetic layers. He immediately recognized the technological possibilities in this discovery and obtained broad patents for GMR-based read heads.

This property was finally realized in graphene, which is composed of a single atomic layer of carbon atoms arranged in a honeycomb lattice. And when Gruenberg applied an external magnetic field, the magnetic fields in both layers lined up, so the external field could control the relative directions of the internal magnetic fields see drawing.

About years ago, the British physicist Lord Kelvin discovered that iron and nickel exhibit a small increase in electrical resistance along the direction of an applied magnetic field and a similar decrease in resistance in the transverse direction.

Nowadays the underlying physics of GMR and the interlayer exchange coupling are broadly understood. The electrons oriented parallel to this field scatter far less than those oriented anti-parallel to it, reducing the electrical resistance for these electrons.

The direction of the field produced by the line of the column is almost parallel to the magnetic moments, and it can not reorient them. In another scheme, the information is kept in the fixed layer, which requires higher recording currents compared to reading currents.

This drawing shows a spin valve with two ferromagnetic FM layers separated by a nonmagnetic NM layer; when the magnetic fields in the two ferromagnetic layers are aligned, as shown in the diagram on the left, half the electrons experience relatively little scattering, leading to a substantial reduction in resistance.

Resistance of the materials is at a minimum when the magnetic moments in ferromagnetic layers are aligned and maximum when they are anti-aligned. Imagine a current of electrons inside a ferromagnet--their velocities point in all different directions, but the average electron velocity points in the direction of the current.

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Giant Magnetoresistance

A parallel orientation is characterized by an electrical state of low resistance, while an antiparallel orientation is a state of high resistance. In the sensing layer, magnetization can be reoriented by the external magnetic field; it is typically made of NiFe or cobalt alloys.The giant magnetoresistance effect is the change of electric conductivity in a system of metallic layers when an external magnetic field changes the magnetization of the ferromagnetic layers relative to each other.

The physicists whose fundamental research made these devices possible, Albert Fert and Peter Gruenberg, won the Nobel Prize in physics in for their discovery of giant magnetoresistance (GMR), the large change in the resistance of a material produced by an external magnetic field.

Giant Magnetoresistance. Giant magnetoresistance is the observation that current flows differently across a multilayer stack consisting of alternating metallic FM/metal bilayers if the magnetization of adjacent ferromagnetic layers is aligned or anti-aligned (Barthélémy et al., ).

Giant magnetoresistance (GMR) is a quantum mechanical magnetoresistance effect observed in multilayers composed of alternating ferromagnetic and non-magnetic conductive layers.

Giant magnetoresistance

The Nobel Prize in Physics was awarded to Albert Fert and Peter Grünberg for the discovery of GMR. Giant magnetoresistance (GMR) is a very small magnetic effect found in thin layers of iron and other materials. It is used to read and write information in hard drives. The GMR effect can be measured when a magnet is used to change the flow of electricity.

Abstract: Giant magnetoresistance (GMR) is a quantum mechanical magnetoresistance the power of the Giant Magneto resistive effect []. Like other magnetoresistive effects, GMR is the change in electrical resistance in response to an applied magnetic field.

Transition metals are extensively studies in many.

Giant magnetoresistance
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