Quantization from resistors in nano contacts

Researchers in the US and France have shown that the resistance of a magnetic wire with a thickness of only a few atomic layers can change in a step-by-step fashion under an external magnetic field.

This result is confirmed as the first validation experiment of the ballistic anisotropy magnetoresistance effect, first hypothesized in 2005. This leap can be exploited quickly. In the future, to increase the capacity of magnetic recording devices (According to the results just published in Nature Nanotechology ).

Ballistic electrons moving in a very thin wire are like a bullet in the barrel - they are forced to move on a certain dimension and are hardly touched or in other words no hindering along the transmission line. If the wire has a thickness of only a few atomic layers, the ability to conduct an electron - conductivity - will be quantized, an integer number (N) of the conductivity of an electron because the energy of the electron is imprisonment in strings in strings is narrow strips and N corresponds to the number of energy ranges above the Fermi level, where conductivity occurs.

Figure 1. Nano contact image with Au electrode, Co conductor and quantization of conductivity over time.

In 2005, Evgeny Tsymbal and colleagues at the University of Nebraska, Lincoln assumed that N numbers could be altered by placing a magnetic field into a very thin wire made of magnetic metals (According to publishing works). in Physical Review Letters 94 (2005) 127203). In those materials, the conduction electrons under the effect of the magnetic field will have to move the energy level against the Fermi level and thus lead to the change of N. Because the conductivity of the wire is proportional to N, the houses The study assumes that it is possible to observe a change in the order of jump of the conductor (in other words, resistance). They call this effect "the ballistic anisotropy magnetoresistance (BAMR) effect - the word" anisotropy "here because this effect depends on the relative angle between the magnetic field and the direction of the current. conduct electricity.

Figure 2. Quantization of conductivity when placed in a saturated magnetic field, pulse rotation contact
around perpendicular axis at a corner frequency.

Recently, Bernard Doudin of the Institute of Physics and Materials Chemistry (Strasbourg) and colleagues at the University of Nebraska, Lincoln observed the BAMR effect in a series of different wires at the atomic size made of Co. In one sample, the researchers measured the change in conductivity corresponding to N = 6, 7 when the direction of the magnetic field changed. The researchers say this reaction is related to the atomic scale deviation in the structure of nanowires and can be explained by Tsymbal's theory of BAMR.

Figure 3. Quantization of conductivity when changing between the angle of the magnetic field and the contact plane.

BAMR will quickly be exploited to create tiny readers for reading data written on magnetic disks and other types. In theory, this could push the density of magnetic information storage to the atomic limit. However, Doudin warns that the sensitivity of the effect to structural changes means that components will have to be manufactured to an atomic level - something that is very difficult at the present time.

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