Kondo effect


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Kondo effect

An unusual, temperature-dependent effect displayed in the thermal, electrical, and magnetic properties of nonmagnetic metals containing very small quantities of magnetic impurities. A striking example is the anomalous, logarithmic increase in the electrical resistivity with decreasing temperature. Other properties, such as heat capacity, magnetic susceptibility, and thermoelectric power, also display anomalous behavior because of the Kondo effect. For these properties, the temperature dependence of a typical dilute magnetic metal (Kondo alloy) differs greatly from the behavior expected of an ordinary metal containing no magnetic impurities.

The Kondo effect has been observed in a wide variety of dilute magnetic alloys. Usually these alloys are made from a nonmagnetic host such as copper, silver, gold, magnesium, or zinc and a small amount of a magnetic metal impurity such as chromium, manganese, iron, cobalt, nickel, vanadium, or titanium. Typical concentrations range from about one to a few hundred magnetic atoms per million host atoms. At higher concentrations, the dilute magnetic alloys may display spin-glass behavior. See Spin glass

The Kondo effect is used in thermometry applications, especially thermocouple thermometers at very low temperatures (that is, millikelvin temperatures). In other applications where the properties of pure metals are studied, the Kondo effect serves as a useful indicator of the metal's magnetic-impurity level.

The problem of understanding the Kondo effect is considered important since it is recognized to be a simpler version of the more complex problem of understanding ferromagnetism in magnetic materials, which is one of the great challenges in physics. Basically the Kondo effect is an example of the most simple possible magnetic system—a single magnetic atom in a nonmagnetic environment. (The alloys used are so dilute that the interaction between different magnetic impurities can be safely ignored.) Although this involves a simple physical model, the problem has required some of the most sophisticated mathematical techniques known to advance its understanding.

An important step in this direction was the development of a partial mathematical solution of the Kondo problem using renormalization field theory techniques. Information gained in this step helped with the final development of a mathematically exact solution of the Kondo problem. The exact solution permits a systematic calculation of all properties (resistivity, thermal conductivity, thermopower, specific heat, magnetic susceptibility, neutron scattering behavior, and so forth) and provides a physical understanding of these properties. The theoretical work on the Kondo problem has been connected with new understanding in a variety of other scientific disciplines such as condensed-matter physics, surface physics, critical phenomena, elementary particle physics, magnetism, molecular physics, and chemistry, where parallels and analogs to the Kondo problem can be identified and utilized. See Critical phenomena, Ferromagnetism, Renormalization

Kondo effect

[′kän·dō i‚fekt]
(metallurgy)
The large anomalous increase in the resistance of certain dilute alloys of magnetic materials in nonmagnetic hosts as the temperature is lowered.
References in periodicals archive ?
For example, we will look at the direct coupling between the spin and molecular vibrational modes, or to the effect of the spin on the Kondo effect.
On the other hand, the Kondo effect favors the formation of singlet states between localized moments and conduction electrons generating a non-magnetic ground state.
Like their larger cousin dots, the atomic-scale transistors exhibit curious electron behaviors, including currents made of electrons moving single file and a phenomenon called the Kondo effect.
4], CdS Nanotubes (nanotubules or fibrils) (329 references) Keywords: actuator, array, atomic force microscopy (AFM) tip, bundles, chemical doping, circuit, color display, composite, conical, crossed, deformed, electronics, electron transport, field-emission display, fullerene, functionalization, junctions, Kondo effect, mesoporous, molecular transistor, molecular wire, multi-walled, nanocable, nanocage, nanocapillarity, nanocoils, nanocomposite, nanofiber, nanomechanic, nanoreactor, nanotube tip, nanotweezers, nanowire, network, phonon spectrum, pipes, quantum dot, quantum resistor, random access memory, ribbons, ropes, Schottky barrier, self-assembling, semiconducting, single-walled, scanning tunneling microscope (STM) tip, synthesis, thermal conductivity Types: Alumina, B, B[C.
Gregory attributes this large current to a remarkable magnetic interaction, the Kondo effect, which in some way orchestrates and facilitates the passage of electrons across the junction.
It also provides a direct means of experimentally studying the Kondo effect itself, which plays a role in superconductivity and other solid-state phenomena.
However, another form of relation between ion and electron spins, called the Kondo effect, could lead to either a magnetic or a non-magnetic low-temperature state and might facilitate the appearance of superconductivity.
Ueda says a consensus is now emerging among theorists that the Kondo effect can dominate and overcome the RKKY effect, provided certain conditions of electron density and electron energy states are met in the band of orbits that contributes most to the magnetic effects of the rare-earth ions, the so-called f band.