The study of the magnetic properties of matter in strong magnetic fields. Part V.— Experiments on magnetostriction in dia- and para-magnetic substances

Abstract

Introduction .—The bismuth rods used for the experiments were of circular cross section, the diameter being about 1 mm. and the length varying from 1 to 2 cm. The rods were prepared in the usual way by extrusion of the metal, and afterwards grown into crystals of the desired orientation by the method described by the author in a previous paper. Except where specially stated, the bismuth used was obtained from Hilger and was 99·993 per cent, pure, and was the same as that used for the experiments on magnetisation described in Part II of this paper. The rods of bismuth were fixed in the apparatus as shown in fig. 2. The two globes which held the rod were made of low melting point Newton alloy; the length of the rod was measured by a travelling microscope. The rods when placed in the extensometer were submitted to a stress produced by the weight of the piston 9, fig. 1, and by different connecting links. The force due to the weight of these parts amounted to 127 gm. which produced a stress of about 15 kg. per square centimetre on the specimen under examination. Later it will be seen that the phenomena observed are actually independent of the stress. The experimental results are represented by curves. The relative increase of length Δ l / l multiplied by 10 6 is taken for the ordinates, and the abscissæ as before, represent the field in kilogauss. In weak magnetic fields, for all orientations of the crystal, we found th at the increase in length followed the square law, and in this case the experimental results could be expressed by the moduli of magnetostriction as defined in Part III, expression (50). The magnetostriction effect was very large and the possible stray effects were small in comparison and could be regarded as negligible.