The paramagnetic properties (in particular the resonance data) of the rare earth ethyl sulfates are considered in the light of a theory in which each ion is assumed to be in a static electric field of $C_{3h}$ symmetry. It is found that this is consistent with the observations in cerium ethyl sulfate, and it is possible to solve that problem to find the magnitude of the interaction of this field with an ion. It is then shown that similar fields give good agreement with the observations in other salts.

Experimental results are reviewed for Fe, Co, Ni, the Co-Ni and Ni-Cu alloy series. Most of the measurements were made at room temperature. In the case of Ni, data are available from about 10°K to 800°K.

In every case studied, the Hall emf consists of a sum of two terms. The first term is proportional to the magnetizing field and has been called the ordinary Hall effect. Its order of magnitude and sensitivity to variations in temperature and in composition are comparable with the Hall effect in nonferromagnetic metals. The second term is proportional to the magnetization and has been called the extraordinary Hall effect.

At room temperature, the extraordinary effect is usually much larger than the ordinary effect. Large changes in the extraordinary effect may be produced by variations in temperature or composition.

In the theory of the ordinary effect, a representation is employed in which conduction may take place in both the $s$- and $d$-bands. This theory appears to be moderately successful in interpreting the experimental data.

Various proposals that have been advanced to account for the extraordinary effect are considered briefly. We consider that a satisfactory physical basis for this phenomenon has not yet been established.

This paper discusses investigations into the detailed changes in domain structure of ferromagnetic material under externally applied stress. The changes in the domain pattern of grain-oriented silicon steel with large grain size were observed and photographed while the specimen was stressed in tension.

Experiments in which the grain under observation had the {110} plane in the surface of the specimen and the $〈110〉$ direction parallel to the specimen axis, along which tension was applied, are discussed in detail. At a load of approximately 0.2 kg/${\mathrm{mm}}^2$ the original domain pattern vanishes. After a transition stage in which, over a certain range of loads, no pattern is visible at all, a new stress-induced domain pattern appears. The behavior of these patterns in horizontal and vertical magnetic fields was studied, and an interpretation of both the transition stage and the stress-induced pattern is given. In these experiments the applied stresses are all within the elastic range of the material. In the plastic range, the knowledge of the stress-induced pattern permits the detection of residual lattice strains in suitably oriented materials.

A striking connection has been found between the magnetic properties and the ultrasonic attenuation properties of a nickel single crystal. The magnetic anisotropy has been detected by measuring the attenuation as a function of applied field intensity. Information about the vibrations of Bloch walls and the number of vibrating walls per unit length has also been obtained. The dependence of the attenuation on magnetic induction for 5-100 mc shear and longitudinal waves propagated in the [110] direction was the same for $B$ parallel to both the [111] and [001] directions. The shear modes induce much greater losses than the longitudinal mode.

Similar measurements on a 3.8 percent Si-Fe crystal showed that the walls in this alloy are not as easily vibrated, i.e., there is a small difference in attenuation between the magnetized and unmagnetized states. At these frequencies this indicates that there is a direct connection between the magnetostrictive constants and the dynamic behavior of Bloch walls.

The elastic constants were computed from velocity measurements, but no $\Delta E$ effect was observed.

Pulsed ultrasonic techniques as described by Roderick and Truell (see reference 4) were used in taking the measurements. The single crystals used were grown from the melt in a hydrogen atmosphere and then oriented so that pure modes of vibration could be propagated.

Measurements of the $\Delta E$ effect and the decrement made by Bozorth, Mason, and McSkimin and by Johnson and Rogers are compared with that expected from a calculation of domain wall relaxations for a distribution of domain sizes as determined by the optical measurements of Williams and Walker. At low frequencies the agreement is good but at high frequencies a second relaxation region is indicated. It is shown that this region is consistent with a domain rotation relaxation and introducing this effect, a good agreement is obtained between theory and experiment for the entire frequency range.

Present theories of magnetization are based largely on energy formulas. These are incomplete because they rely on a calculation of magnetization work in the absence of strain and of strain work in the absence of magnetization. The present paper summarizes and relates to magnetization theory a calculation, already published elsewhere, in which magnetization and strain are assumed from the start to be present simultaneously; furthermore forces are calculated directly, without use of energy arguments until the properties special materials are considered. An important result is that the separation of the force on part of a body into a "magnetic" force and a force derivable from "stresses" can be accomplished in more than one way. the theory confirms the traditional results for fluids; but for elastic solids, it yields terms not present in the formulas of the traditional theory. These terms may be important in the magnetization process. For a uniformly magnetized ellipsoid they lead to a nonuniform magnetostriction "form effect" with a mean strain equal to the strain calculated by Becker.

The temperature range of magnetic susceptibility measurements has been extended from 1450°C to 1850°C. In the range from 25°C to the highest temperature measured, the susceptibilities of V, Nb, and Ta decrease with increasing temperature, while the susceptibilities of Mo and W increase. A periodicity in the sign of the temperature coefficient of the magnetic susceptibility of the transition elements is discussed in relation to various theories of metals.