Charge carriers (blue electrons and red holes) in a conductor are deflected from their original flow (green arrow) by a magnetic field (black arrows). “The faster the electrons are moving, the more strongly they are deflected from the original direction of flow and the greater is the electric resistance,” said researcher Yulin Chen of the University of Oxford. “This effect is especially large in niobium phosphide, as the material possesses especially fast electrons.” Note: The red arrow may be the wrong way around.
German scientists have discovered giant magnetoresistance – the effect used in hard drive read heads – in niobium phosphide. They also identified graphene-like carriers in the 3D material.
“Until now, the computer industry has used various materials stacked on top of each other in a filigree structure to achieve this effect. Now, Max Planck scientists in Dresden have observed a rapid increase in resistance by a factor of 10,000 in a non-complex material, namely niobium phosphide,” said the Max Planck Institute for Chemical Physics of Solids
Magnetoresistance of 850,000% was seen at 1.85K, and 250% at room temperature, in a magnetic field of up to 9T, without any signs of saturation, and with 5x106cm2/Vs carrier mobility – according to ‘Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal candidate NbP‘, a paper in Nature Physics.
The reason the team picked NbP was its high carrier mobility. It has ‘relativistic electrons’ that move 300km/s – one thousandth the speed of light.
In a magnetic field, charge carriers are deflected by the Lorentz force which causes electrons to start flowing in the ‘wrong’ direction, according to the Institute, as the magnetic field is ramped up – increasing electric resistance.
“The faster the electrons in the material move, the greater the Lorentz force and thus the effect of a magnetic field,” said Max Planck researcher Binghai Yan.
For their investigations, the scientists used the Dresden High Magnetic Field Laboratory, the High-Field Magnet Laboratory at Radboud University Netherlands, and the Diamond Light Source in Oxfordshire.
In the process, they discovered why the electrons are so fast and mobile – some electrons in this material, known as a Weyl metal, act as if they have no mass.
“The effect that we’ve discovered in niobium phosphide could certainly be improved by means of skilled material design. This material class therefore has enormous potential for future applications in information technology,” said Yan.
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