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| Neel temperature | |
|---|---|
| Name | Néel temperature |
| Other names | Neel point |
| Typical range | few kelvin – several hundred kelvin |
| First reported | 1936 |
| Discoverer | Louis Néel |
Neel temperature The Néel temperature is the characteristic temperature at which an antiferromagnetic material undergoes a phase transition from an ordered antiferromagnetic state to a disordered paramagnetic state. It marks a thermodynamic boundary analogous to the Curie temperature for ferromagnets and is central to the study of magnetism in condensed matter physics, materials science, and solid-state chemistry.
The Néel temperature, denoted T_N, identifies the temperature above which long-range antiparallel spin order collapses and thermal fluctuations dominate, producing paramagnetic behavior. In the context of crystalline solids and magnetic compounds, T_N is influenced by exchange interactions, crystal symmetry, and magnetic anisotropy; these factors are central to analyses by figures such as Louis Néel, and concepts developed within institutions like the French Academy of Sciences and laboratories at the University of Oxford or Bell Labs. The transition at T_N often accompanies changes in thermodynamic observables measured in facilities including the National Institute of Standards and Technology and appears in phase diagrams used by researchers at the Max Planck Society and Argonne National Laboratory.
Theoretical descriptions of T_N derive from models including the Heisenberg model, the Ising model, and the Hubbard model, all of which were extensively studied by theorists at the Institute for Advanced Study and universities such as Princeton University and Cambridge University. Mean field theory yields a first approximation for T_N by relating exchange constants to ordering temperatures; refinements use renormalization group methods developed by proponents like Kenneth Wilson and the framework of Landau theory of phase transitions. Quantum Monte Carlo simulations performed on supercomputing centers like the Oak Ridge National Laboratory and cluster algorithms from groups at MIT provide numerical estimates for T_N in low-dimensional and frustrated lattices, while spin-wave theory and linear response calculations are applied in publications from the Journal of Physics C and Physical Review Letters.
Experimental determination of T_N employs magnetometry in instruments from manufacturers such as Quantum Design and neutron scattering at user facilities like the Institut Laue–Langevin and the Oak Ridge National Laboratory Neutron Sciences. Techniques include DC and AC susceptibility measurements, specific heat calorimetry in cryostats used by groups at CERN and Brookhaven National Laboratory, Mössbauer spectroscopy associated with researchers at Columbia University, muon spin rotation studied at the Paul Scherrer Institute, and nuclear magnetic resonance methods developed in laboratories at Stanford University and Harvard University. Elastic and inelastic neutron diffraction patterns reveal magnetic Bragg peaks that vanish at T_N, a method pioneered in experiments at the Los Alamos National Laboratory and described in reports from the European Synchrotron Radiation Facility.
Near T_N materials display critical phenomena characterized by power-law divergences of susceptibility and correlation length, with critical exponents that belong to universality classes investigated by scholars at Cornell University and the University of California, Berkeley. Renormalization group analysis links these exponents to dimensionality and symmetry groups such as O(3) relevant to Heisenberg antiferromagnets; studies published in Reviews of Modern Physics and Nature Physics compare experimental exponents from compounds measured at facilities like the ISIS Neutron and Muon Source and theoretical predictions from teams at the Perimeter Institute. Finite-size scaling observed in thin films and heterostructures fabricated at centers like IBM Research and Samsung Advanced Institute of Technology modifies the apparent T_N, as reported in collaborations with the National High Magnetic Field Laboratory.
T_N varies widely across classes of materials: transition metal oxides such as NiO and FeO often have high Néel temperatures, rare-earth intermetallics investigated at the Paul Scherrer Institute show complex magnetic ordering with lower T_N values, and low-dimensional quantum magnets including chains and ladders studied at ETH Zurich and Tokyo Institute of Technology exhibit reduced or suppressed ordering due to enhanced quantum fluctuations. In strongly correlated electron systems like cuprates researched at MIT and Bell Labs, antiferromagnetic parent compounds set the stage for superconductivity upon doping; heavy fermion materials probed at Los Alamos National Laboratory and organic salts examined at University of Tokyo display interplay between Kondo screening and antiferromagnetism that shifts T_N.
Knowledge of T_N informs design and operation of spintronic devices developed at Hitachi, NEC Corporation, and research groups at University of Cambridge, where antiferromagnets are exploited for high-frequency dynamics and stability against external magnetic fields. Magnetic refrigeration concepts evaluated at Los Alamos National Laboratory and sensing technologies used by companies like Honeywell consider the magnetic entropy changes near ordering temperatures. Antiferromagnetic materials with tailored T_N are integrated into heterostructures for exchange bias in magnetic recording studied at Seagate Technology and spin-transport experiments at Oak Ridge National Laboratory.
Category:Magnetism