Paramagnetic Body Research Articles

Contemporary Advances in Physics, XXX-The Theory of Magnetism*

The topic of this article is the explanation of magnetism as ordinarily observed — to wit, the magnetization of pieces of matter of ordinary dimensions — by ascribing magnetic moment to the individual molecules, atoms, and electrons of which matter is composed. For paramagnetic bodies it is postulated that the individual atoms are magnets of which the orientation, but not the strength, is altered in the presence of a magnetic field; the theory is so successful as to make it possible to calculate, from magnetization-curves, values for the magnetic moments of these atoms which agree admirably with those deduced from spectroscopic theory and from experiments of other types. For ferromagnetic bodies the same postulate is made, but it is necessary in addition to recognize the existence of huge interatomic forces of which very little is known, so that a large proportion of the science of ferromagnetism still lies beyond the scope of atomic theory. For diamagnetic bodies the phenomena are interpreted in a simple and effective manner, as an immediate corollary of the well-known structure of the atom.

The study of the magnetic properties of matter strong magnetic fields.—I.—The balance and its properties

In several previous communications the author has described a method by which magnetic fields up to 300,000 gauss could be obtained for a duration of time of the order of 1/100 of a second. It was shown that these magnetic fields, in spite of the shortness of their duration, can be applied to the study of different phenomena such as the change of resistance, the Zeeman effect, and others. The present paper describes a number of investigations which have been made on different substances, extending the application of intense magnetic fields to the study of magnetic susceptibility and magnetostriction. The interest in measuring the susceptibility of different substances in strong magnetic fields lies mainly in seeing whether the linear law of magnetisation for ordinary para- and diamagnetic substances holds for higher fields, and also in the investigation of the saturation of paramagnetic bodies at low temperatures, with a view to determining the elementary magnetic moments. In the present communication a method of measuring the magnetic susceptibility is described and experimental results are given which verify the linear law of magnetisation for several paramagnetic and diamagnetic substances. The saturation of iron and nickel in strong fields is also studied. As will be seen later, the possibility of making these measurements in such a small fraction of time results from the increased magnitude of the phenomenon itself. The most direct method for measuring the magnetic susceptibility is to record the force on a magnetised body in an inhomogeneous magnetic field. In the usual experiments at room temperature this force is only a few hundred dynes, but when fields reach the magnitude of 300 kilogauss the force becomes several grams, and is then sufficiently large to be measured with fair accuracy even in short times of the order of 1/100 of a second. In this paper a special type of balance will be described by which these measurements are made possible.

Molecular and Cosmical Magnetism

DR. CHAPMAN'S important letter (NATURE, November 25, 1920) bases a theory of cosmical magnetism on the presence of gyroscopic magnetic elements proved to exist in ferro-magnetic substances by my investigations on magnetisation by rotation. But he considers my fundamental theory to require serious modification. As I understand his letter, however, his theory is identical with mine (see Science, Vol. xlviii., p. 304, 1918, and references) except as to paramagnetic and diamagnetic bodies. He has, I think, confused my treatments of magnetic intensity and intensity of magnetisation.

Molecular and Cosmical Magnetism

I FULLY agree with Prof. Barnett's statement of the theory of magnetisation by rotation, and regret that through misunderstanding his treatment of magnetic intensity I suggested that his theory required modification. I am glad to know that he contemplates experiments on the rotation of hot bodies; this point, and the greater possibilities afforded if the magnetic elements remain intact at high temperatures, are the matters to which chiefly I wished to direct attention. Experiments made here with Dr. Oxley have negatived my suggestion that diamagnetic and paramagnetic bodies should also show magnetisation on rotation, thus confirming the previous results mentioned by Prof. Barnett; experiments on hot ferro-magnetic bodies are not yet advanced sufficiently to state whether they support the view that the earth's magnetism may depend on its high internal temperature. Further trial seems to preclude the possibility of trustworthy calculation at present, and the view must be tested by experiment. Until this is done it seems useless to enter into further details of the earth's field and its secular variation.

The Magnetic Balance of MM. P. Curie and C. Cheneveau

This balance is intended for the determination of the coefficient of specific magnetization, susceptibility, and permeability of feebly paramagnetic and diamagnetic bodies. The body under investigation is suspended from one arm of a torsion balance, which measures the force exerted on the body when it is placed in the non-uniform field of a permanent magnet. The torsion balance is formed by a horizontal rod suspended by a long fine platinum wire and carrying at one end a hook from which the substance under investigation can be suspended in a small enclosing glass tube. On the other end of the torsion arm a copper sector is fixed which moves between the poles of an auxiliary magnet and thus provides efficient damping. A second branch arm is also provided upon which may be placed suitable counterweights to balance the specimen. The suspension carries a mirror, and the movements are read on a translucent scale in the ordinary way. The magnetic field is that of a large circular permanent magnet mounted in such a way that the vertical gap may be made to describe a semicircle of radius equal to the length of the torsion arm, and the movements of this magnet are controlled by the observer at the screen by means of cords. An empty containing tube is first mounted on the balance, and the maximum deviation on both sides of the zero is obtained by bringing up the magnet towards each side of the specimen. The tube is now filled to a given mark with a known mass of pure distilled water and the variations observed as before. The water is now replaced by a known mass of the substance to be examined occupying the same volume or the same vertical height, and again the deviations are observed. The paper indicates how the value of K may be calculated from these observations. Experiments have been performed with various metals and alloys, and the results are tabulated and discussed in the paper.

Note on the use of the electro-magnet for the extraction of para-magnetic foreign bodies in the air passages

Note on the use of the electro-magnet for the extraction of para-magnetic foreign bodies in the air passages

Experimental researches in electricity. Twenty-sixth series. On magnetic conducting power and atmospheric magnetism

The remarkable results respecting oxygen and nitrogen described in the last Series, and the absence of any change of volume under strong magnetic action, led the author to apply for a time the idea of conducting power to the magnetic phenomena there described, meaning by that phrase the capability which bodies possess of affecting the transmission of the magnetic force without any reference to the process by which that transmission is effected; and assuming that two bodies are at the same time in the magnetic field, and that one displaces the other, he considers the result as a differential effect of their difference in conducting power. If a free portion of space be considered with lines of equal magnetic force passing across it, they will be straight and parallel lines. If a sphere of paramagnetic matter be placed in such a space, they will gather upon and in the sphere, being no longer parallel in their course, nor of equal intensity in every part; or if a sphere of diamagnetic matter replace the former sphere, the lines of force will open out where the sphere is, being again no longer parallel in direction nor uniform in force. When the field of magnetic force is formed between the opposite flat ends of two large magnetic poles, then these are affected, and the globes also, and there are mutual actions; a paramagnetic body, if a little elongated, points axially and tends to go to the iron walls of the field, whilst a similar diamagnetic body points equatorially, and tends to go to the middle of the field. Paramagnetic bodies repel each other, and so also do diamagnetic bodies; but one of each class being taken, they attract one another.