Thermal Agitation Energy Research Articles

Investigation of the Magnetic Refrigerant for the Ericsson Magnetic Refrigerator

In the temperature range above ∼20 K, the Ericsson magnetic refrigeration cycle has to be adopted instead of the Carnot cycle, because the lattice entropy becomes no longer negligible as compared with the magnetic entropy. Moreover, in this range since the thermal agitation energy ∼kT of spin also increases, the ferromagnetic materials have to be used for the refrigerant to obtain large entropy change enough to refrigerate. However, temperature variation of the magnetic entropy change of ferromagnetic material is not suitable for the Ericsson cycle. In the present paper we will give the answers to the following questions; (1) what kinds of ferromagnets must be used for the refrigerant? (2) what kind of method to compose the refrigerant using those ferromagnets is promising?

Magnetic properties and noise in cylindrical Permalloy thin-film magnetometers

The magnetic properties and low-frequency noise measurements of thin films of Permalloy are described. The films are obtained by electrodeposition. They are polycrystalline and single domain. The noise due to the film is shown to be an increasing function of the dispersion angle α <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</inf> . A model for the noise mechanism taking into account the magnetostatic stray field arising in the grain boundaries and the thermal agitation energy is given. It is in qualitative agreement with the experimental results.

Optical Observation of the Debye Heat Waves in Crystals

MANY years ago1, it was pointed out by one of us that Debye's concept identifying the thermal energy of a solid with the energy of elastic vibrations within it having a wide range of frequencies has an important optical consequence, namely, that a beam of light traversing a transparent solid would be scattered to an extent depending upon the energy of thermal agitation. This conclusion was also verified experimentally in a semi-quantitative fashion2. The principal experimental difficulty in studying the subject was that of obtaining crystals sufficiently large and at the same time free from imperfections or inclusions, these conditions being necessary to prevent the feeble thermal opalescence being overpowered by parasitic diffuse light. The same difficulty appears in attempting to investigate the thermal opalescence in crystals by spectroscopic methods. The elastic waves, longitudinal or transverse as the case may be, which scatter the light being progressive, they should give rise to Brillouin-Doppler shifts of optical frequency corresponding to their respective acoustic velocities. If parasitic light be present, the unmodified scattering and the hyper-fine structure components usually accompanying the same would overpower the Brillouin-Doppler components to be expected.

Dispersion of Sound Velocity in Liquids

As is now well known1, the spectral character of monochromatic light scattered by many liquids exhibits an observable change as the result of such scattering; an instrument of sufficiently high resolving power, for example, a Fabry-Perot etalon2, indicates the presence of Doppler-shifted components on either side of the main radiation. From this we are able to infer that sound waves of very high frequency represent a considerable part of the energy of thermal agitation in such liquids. The frequency of the sound-waves actually revealed by this method depends on the wave-length of the incident light, the angle of scattering and the liquid employed; in most actual cases, it lies within the frequency range 1,000–10,000 megacycles per second.

Dependence of Electron Emission from Metals Upon Field Strengths and Temperatures

This paper contains a full presentation of the reasons for believing, contrary to results recently obtained elsewhere, that field currents are only independent of temperature up to about 1100\ifmmode^\circ\else\textdegree\fi{}K, and that at that temperature the energy of thermal agitation begins to assist the fields appreciably in causing the escape of electrons from metals. The precise form of function describing this dependence is not accurately determinable experimentally, but the form originally suggested by us fits the facts of observation thus far known satisfactorily, not better, however, than does the theoretical form suggested by Houston.

Dependence of Electron Emission from metals upon Field Strengths and Temperatures

This paper contains a full presentation of the reasons for believing, contrary to results recently obtained elsewhere, that field currents are only independent of temperature up to about 1100°K, and that at that temperature the energy of thermal agitation begins to assist the fields appreciably in causing the escape of electrons from metals. The precise form of function describing this dependence is not accurately determinable experimentally, but the form originally suggested by us fits the facts of observation thus far known satisfactorily, not better, however, than does the theoretical form suggested by Houston.

The magnetic susceptibility of the alkali metals

In a recent paper, Miss L. Crow found the alkali metals to be diamagnetic: they seemed in this respect to resemble copper, silver and gold, which have in the vapour state one Bohr magneton per atom, but are diamagnetic when solidified. In view of the statement made by Miss Crow that the susceptibility of the glass containers used was negligibly small, it seemed to us necessary to repeat her work. The following paper gives the results of our investigation. In a series of experiments, Gerlach and Stern, and also Taylor, showed that for elements of the first column the vapour molecules possess one Bohr magneton m 0 = 5550/N gauss cm., N being Avogadro’s number. When placed in a magnetic field H the velocity of the valence electron increases, and the energy of the molecule changes by the amount ( m 0 H) + ( e 2 H 2 /8 mc 2 )Σ r 2 , m being the mass of the electrons, e its charge, c the velocity of light, and r the distance from the nucleus. The second member, the diamagnetic effect, is usually negligible. The first term, the paramagnetic effect, leads to an orientation of the molecule parallel to the magnetic field, an orientation which remains, however, incomplete on account of the energy of thermal agitation and the collisions of the atoms. In the case of the alkali vapours for which the molecules are free to orientate themselves in any direction, the molecular susceptibility may be shown to be X m = 1/3 N m 0 2 / k T. In solid bodies the number of positions which the molecule is free to assume is limited by the action of the neighbouring atoms with which it composes the crystal lattice, and the magnetic field may not be able to overcome the forces in the solid body and not succeed in orientating the magnetons. The paramagnetic properties are then hidden, and the diamagnetic factor may become predominant. Furthermore, lower electron shells become important, as is known in the case of the rare earths.

Illustrations of the Dual Theory of Metallic Conduction

The occurrence of a Peltier effect with change of direction within a metal crystal, which effect Bridgman has recently noted and which he has considered incapable of explanation by any of "our ordinary pictures of electrical conduction," is readily explained by the dual theory, through a formula published several years ago. Millikan's recent announcement that, according to experiments and reasoning of his own, most of the conductive electrons within metals do not share the energy of thermal agitation, while the "thermions," "presumably responsible for the Peltier and thermo-electric effects," do share this energy, tends to confirm views which the author has long held and repeatedly expressed. These facts seem to indicate that the time is opportune for a more continuous and better illustrated statement of the dual theory of metallic conduction than has yet been given. This statement reviews briefly what the theory has had to say concerning the Volta effect, Richardson's derivation of his formula for thermionic emission, and the thermo-electric pseudo equation $P=T$ $\frac{\mathrm{dV}}{\mathrm{dT}}$, applying everywhere the mass law of equilibrium between electrons, ions and atoms within a metal. It then undertakes to show how the Thomson effect, the Peltier effect, the electric conductivity and the thermal conductivity of a given metal may be rationally connected by means of a set of six equations containing six constants characteristic of the metal, the equations serving for the determination of the constants. It shows in particular how a theory of heat conduction, with a definite formula for thermal conductivity, grows out of the more fundamental conceptions of the dual theory. It applies the machinery of the dual theory to the results of Bridgman's experiments on changes of electrical, thermal and thermoelectric properties of metals under high pressure, showing explicitly how the corresponding changes of the "characteristic constants" can be found and what is the nature of these changes in particular instances. Two general results of importance appear from this discussion. The first, which was predicted, is that, as a rule, compression of a metal reduces the latent heat of the ionization process within it. The conception of thermal conductivity as the product, in a general way, of electric conductivity and heat of ionization, goes far to explain why the two conductivities, though so closely related, are so differently affected by certain changes of condition. The second general conclusion from the study of Bridgman's data is that, contrary to expectation, compression of a metal increases, as a rule, the ratio of free-electron conductivity to total electric conductivity. This evidence seems to give support to the idea, already familiar, that the free electrons may go through, not necessarily between, the atoms in their progress through a metal. This conception, taken with the consideration that latent heat of ionization diminishes with fall of temperature, suggests that the supraconductive state may be one in which the distinction between "free" electrons and "associated" electrons disappears, the metal being, as regards all the conductive electrons, in a state of flux.The theory here set forth, if it is to account for the whole of thermal conduction in metals, appears to require the heat of ionization within a metal to increase with increase of temperature, even when expansion is prevented by increase of pressure.The dual theory indicates that photo-electric emission should be nearly independent of temperature but suggests the following revision of Richardson's thermionic emission formula, $a$ being a constant: $i=A{T}^{\frac{1}{2}}{\ensuremath{\epsilon}}^{\frac{\ensuremath{-}{b}_{0}}{R}}=A{T}^{\frac{1}{2}}{\ensuremath{\epsilon}}^{\ensuremath{-}a}{\ensuremath{\epsilon}}^{\frac{\mathrm{aT}}{T}}{\ensuremath{\epsilon}}^{\frac{\ensuremath{-}{b}_{0}}{T}}={A}^{\ensuremath{'}}{T}^{\frac{1}{2}}{\ensuremath{\epsilon}}^{\frac{\ensuremath{-}({b}_{0}\ensuremath{-}aT)}{T}}$

Laws Governing the Pulling of Electrons out of Metals by Intense Electrical Fields

Current from thoriated tungsten filaments in vacuum, due to radial fields of up to two million volts per cm. — Three filaments were tested, each .00123 cm in diam. and suspended under tension in the axis of a copper cylinder of 1.6 cm diam. From the dimensions, the radial field at the surface of the filament was 228 times the applied potential difference. The electron currents pulled from the tungsten by the high fields (field currents) rise steadily from 10^-12 to 10^-3 amp. as the field is increased from about 400 to 1100 kv/cm. In the dark, luminous spots were seen on the anode, indicating that these currents come from a few active surface spots. The field current (for a given voltage) depends on the value of the maximum field current previously drawn from it (conditioning current), being reversibly reproducible below the conditioning current. The higher the conditioning current, the lower the field current. A previous heating to high temperatures (2400°C) decreases the field current and also decreases the slope of the current-voltage curve. Both effects (current and heating) show fatigue. Variation with temperature of the filament, to 800°C. The field currents are completely independent of temperature up to 700°, but a temperature of 800° increases the currents due to a given field when this is sufficiently large, by a factor which is roughly independent of the current (10-8 to 10-4 amp.). Electron theory. In explanation of these results, it is suggested that the field currents are due to conduction electrons pulled from minute peaks on the surface, the fatigue effects of both current treatment and heat treatment being due to the rounding off of these peaks by positive ion bombardment or by temperature. Chemical changes may also alter the surface. The lack of dependence of field currents upon temperature furnishes strong evidence that most of the conduction electrons do not share in the energy of thermal agitation. The thermions, however, do share in this energy; they are presumably responsible for the Peltier and thermo-electric effects. In this theory it is assumed that conduction electrons follow the same sort of quantum laws in their escape from the solid as do atoms of a light element at temperatures far below the boiling point.

An Experimental Confirmation of the Kinetic and Molecular Theories of Magnetism

CURIE'S law states that ferromagnetics above the critical temperature behave in such a way that the susceptibility (k) is inversely proportional to the absolute temperature (T), in short, that the product k. T is a constant. The physical meaning of this law is that when the molecular magnets have complete freedom of rotational movements, the energy of magnetisation is then only opposed by the energy of thermal agitation and, consequently, any given state is a state of equilibrium.