What is "nanomagnet"

n. (context physics English) A nanoscale magnet

A nanomagnet is a submicrometric system that presents spontaneous magnetic order ( magnetization) at zero applied magnetic field ( remanence).

The small size of nanomagnets prevents the formation of magnetic domains (see single domain (magnetic)). The magnetization dynamics of sufficiently small nanomagnets at low temperatures, typically single-molecule magnets, presents quantum phenomena, such as macroscopic spin tunnelling. At larger temperatures, the magnetization undergoes random thermal fluctuations ( superparamagnetism) which present a limit for the use of nanomagnets for permanent information storage.

Canonical examples of nanomagnets are grains of ferromagnetic metals ( iron, cobalt, and nickel) and single-molecule magnets. The vast majority of nanomagnets feature transition metal ( titanium, vanadium, chromium, manganese, iron, cobalt or nickel) or rare earth ( Gadolinium, Europium, Erbium) magnetic atoms.

Attending to the number of magnetic atoms, the smallest nanomagnets reported so far are double decker phthalocyanes with only one rare earth atom. Canonical single-molecule magnets are the so-called Mn12 and Fe8 systems, with 12 and 8 transition metal atoms each and both with spin 10 (S = 10) ground states.

The phenomenon of zero field magnetization requires three conditions:

1. A ground state with finite spin
2. A magnetic anisotropy energy barrier
3. Long spin relaxation time.

Conditions 1 and 2, but not 3, have been demonstrated in a number of nanostructures, such as nanoparticles, nanoislands, and quantum dots with a controlled number of magnetic atoms (between 1 and 10).

A nanomagnet can have enhanced electronic properties due to size effect, such as long spin relaxation time of conduction electron, which may be useful for nano-scale spintronic device.