ferromagnetism

ferromagnetism
Name	Ferromagnetism
Type	Physical phenomenon
Discovered	Ancient times; quantified 19th century
Discoverer	William Gilbert, Hans Christian Ørsted, André-Marie Ampère, Michael Faraday

ferromagnetism Ferromagnetism is a class of magnetic behavior exhibited by certain materials that display spontaneous magnetization and strong, long-range interactions among magnetic moments. It underlies technologies from motors to data storage and has been studied by figures associated with Royal Society, University of Oxford, University of Copenhagen, École Polytechnique, University of Cambridge and institutions such as Max Planck Society, Bell Labs, MIT, Caltech and National Institute of Standards and Technology. Research on ferromagnetism connects to experimental landmarks including work by Charles-Augustin de Coulomb, James Clerk Maxwell, Pierre Curie, Paul Langevin, Ernest Rutherford, Niels Bohr, P. W. Anderson, Lev Landau and John Bardeen.

Introduction

Ferromagnetism manifests when atomic-scale magnetic moments align to produce a macroscopic magnetic moment similar to effects first noted by Pliny the Elder and later systematized by William Gilbert and measured by Hans Christian Ørsted, André-Marie Ampère and Michael Faraday. Modern descriptions build on concepts developed at institutions such as Royal Institution, Trinity College Dublin, University of Göttingen, University of Paris, University of Berlin and Oxford University Press-level scholarship. Historic experiments performed in locations like Greenwich Observatory, Royal Observatory, Edinburgh, Kew Observatory and laboratories at University College London helped establish empirical laws and materials catalogs used by industries including Siemens, General Electric, IBM, Intel and Hitachi.

Fundamental Concepts

Key elements include alignment of magnetic moments, domain formation, hysteresis loops, remanence and coercivity; early quantitative approaches were advanced at École Normale Supérieure, University of Vienna, Princeton University, Harvard University and University of Chicago. Magnetic domains were imaged in studies tied to instruments from Cambridge Scientific Instrument Company and techniques developed alongside work of Ernst Ruska, Robert Koch, Fritz Haber and Wilhelm Röntgen. The role of exchange interactions and spin degrees of freedom was elucidated in theoretical work associated with Heisenberg, Wolfgang Pauli, Enrico Fermi, Niels Bohr and experimental confirmations at CERN, Los Alamos National Laboratory, Brookhaven National Laboratory and Lawrence Berkeley National Laboratory.

Theoretical Models and Mechanisms

Models explaining alignment include the Heisenberg model, Ising model, mean-field (Weiss) theory and itinerant electron models developed at University of Leipzig, Institut Henri Poincaré, Columbia University, University of Illinois Urbana–Champaign and Johns Hopkins University. Contributions by Pierre Weiss, Erwin Schrödinger, Lev Landau, Felix Bloch, John Hubbard, Philip W. Anderson, Eugene Wigner and J. B. Goodenough tied magnetism to band structure and electron correlation studies performed at Bell Labs, AT&T Laboratories, IBM Research and national laboratories. Quantum mechanical descriptions draw on formalisms by Paul Dirac, Werner Heisenberg, Wolfgang Pauli and applications in condensed matter theory pursued by groups at Princeton Institute for Advanced Study, Perimeter Institute, Imperial College London and Weizmann Institute of Science.

Materials and Properties

Common ferromagnetic materials include iron, cobalt, nickel and their alloys; studies of steels and rare-earth magnets engaged firms and labs such as ThyssenKrupp, ArcelorMittal, Mitsubishi Heavy Industries and researchers at Toyota Central R&D Labs and Hitachi Global Storage Technologies. Rare-earth–transition-metal compounds explored at Bell Labs, Los Alamos National Laboratory and Toyota rely on elements cataloged by International Union of Pure and Applied Chemistry and procurement via suppliers linked to Rio Tinto and BHP. Microstructure, grain size, defects and impurity effects have been characterized using instrumentation from Bruker, JEOL, Thermo Fisher Scientific and beamlines at facilities like European Synchrotron Radiation Facility, SLAC National Accelerator Laboratory and Advanced Photon Source.

Temperature Effects and Phase Transitions

Curie temperature behavior and critical phenomena were investigated by Pierre Curie and later formalized in renormalization group work by Kenneth G. Wilson, Leo Kadanoff, Michael Fisher and Kenneth Wilson's collaborators affiliated with Brookhaven National Laboratory, Princeton University and Stanford University. Experiments on phase transitions used cryogenic systems developed at CERN, Brookhaven, National High Magnetic Field Laboratory and facilities supported by National Science Foundation, European Commission and national ministries. Applications of statistical mechanics to ferromagnetic ordering reference methods from John von Neumann, Kurt Gödel-era mathematics and computational advances at Los Alamos National Laboratory and Sandia National Laboratories.

Applications and Technology

Ferromagnetism enables electric motors, transformers, magnetic storage, spintronic devices and sensors used by companies such as Toyota, General Motors, Siemens, Bosch, Hitachi, Samsung, Western Digital and Seagate Technology. Spintronics and magnetoresistance research link to discoveries at IBM Research, University of Groningen, Tohoku University, Kobe University and projects funded by agencies like DARPA and European Research Council. Magnet-based medical imaging, magnetic resonance and nanoparticle therapies interface with hospitals and centers including Mayo Clinic, Johns Hopkins Hospital, Massachusetts General Hospital, Karolinska Institutet and Cleveland Clinic.

Experimental Techniques and Measurement Methods

Characterization techniques include vibrating-sample magnetometry, superconducting quantum interference devices, ferromagnetic resonance, Mössbauer spectroscopy and neutron scattering performed at Oak Ridge National Laboratory, Institut Laue–Langevin, ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Argonne National Laboratory and university laboratories at University of California, Berkeley, Imperial College London, ETH Zurich and Technical University of Munich. Instrumentation and standards are supported by organizations such as National Institute of Standards and Technology, International Electrotechnical Commission, IEEE and commercial vendors like Agilent Technologies and Oxford Instruments.

Category:Magnetism