Persistent current

In resistive materials, persistent currents can appear in microscopic samples due to size effects.

Therefore, in the macroscopic Maxwell's equations, it is purely a choice of mathematical convenience, whether to represent persistent currents as magnetization or vice versa.

[1] This principle is used in superconducting electromagnets to generate sustained high magnetic fields that only require a small amount of power to maintain.

The persistent current was first identified by H. Kamerlingh Onnes, and attempts to set a lower bound on their duration have reached values of over 100,000 years.

This hypothesis has been offered for explaining the singular magnetic properties of nanoparticles made of gold and other metals.

[6] This kind of persistent current was first predicted to be experimentally observable in micrometer-scale rings in 1983 by Markus Büttiker, Yoseph Imry, and Rolf Landauer.

[6] Experimental evidence of the observation of persistent currents were first reported in 1990 by a research group at Bell Laboratories using a superconducting resonator to study an array of copper rings.

"These are ordinary, non-superconducting metal rings, which we typically think of as resistors, yet these currents will flow forever, even in the absence of an applied voltage.

Persistent current schematic. The green arrow indicates the direction of static applied magnetic field B which allows a net current I (blue arrow) to flow and create a magnetization M (black arrow) by breaking the symmetry between clockwise and counterclockwise currents. The yellow dot represents an electron traversing the disordered material of the ring (green stars) without dissipation . A typical ring current is 1 nanoampere for a ring diameter of 0.6 micrometer at a temperature below 0.5 kelvin . [ 3 ]