Supermagnetism

• Published in: Journal of physics. D, Applied physics Vol. 42; no. 1; pp. 013001 - 013001 (28)
• Main Authors: Bedanta, Subhankar, Kleemann, Wolfgang
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 07.01.2009; Institute of Physics
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Diamagnetism, paramagnetism and superparamagnetism; Exact sciences and technology; Magnetic properties and materials; Magnetic properties of nanostructures; Physics; Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.); Dipole dipole interaction; Spin glasses; Magnetization; Strong interactions; Tunnel effect; Superspin glass; Magnetic hysteresis; Superparamagnetism; Superferromagnetism; Nanoparticles; Magnetic particles; Particle interactions; Magnetic anisotropy; Magnetic domains; Ferromagnetism; Exchange interactions
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/42/1/013001

An ensemble of nanoparticles in which the inter-particle magnetic interactions are sufficiently weak shows superparamagnetic behaviour as described by the Neel-Brown model. On the contrary, when inter-particle interactions are non-negligible, the system eventually shows collective behaviour, which overcomes the individual anisotropy properties of the particles. At sufficiently strong interactions a magnetic nanoparticle ensemble can show superspin glass (SSG) properties similar to those of atomic spin glass systems in bulk. With a further increase in concentration, but still below physical percolation, sufficiently strong interactions can be experienced to form a superferromagnetic (SFM) state. SFM domains in a non-percolated nanoparticle assembly are expected to be similar to conventional ferromagnetic domains in a continuous film, with the decisive difference that the atomic spins are replaced by the superspins of the single-domain nanoparticles. In this review we highlight the most important developments in the field of supermagnetism, which comprises three fascinating subjects: superparamagnetism, SSG and superferromagnetism.