64 



EXPLORATION GEOPHYSICS 



DIAMAGNETIC 

 FORCE LINES DIVERGE FROM BODY 

 REPULSION 



PARAMAGNETIC 

 FORCE LINES CONVERGE INTO BODY 

 ^ ATTRACTION 



DIVERGENT 

 FIELD 



DIVERGENT 



FIELD 



UNIFORM FIELD 



UNIFORM FIELD 



Fig. 5. — Showing the behavior of diamagnetic and paramagnetic bodies in a divergent 

 and in a uniform magnetic field. Forces acting on bodies tend to cause rotation or 

 movement, as shown by arrows. (After Loeb.) 



field acting on them. The lines of the field converge into such bodies. 

 Examples of paramagnetic materials are platinum, aluminum, and 

 manganese. 



Ferromagnetic materials show such pronounced paramagnetic reactions 

 that few substances have been designated by this term, which means 

 literally magnetic like iron. Test pieces of magnetite, steel, iron, nickel, or 

 Huesler's alloy, for example, will show their ferromagnetic character by 

 being strongly attracted into a divergent magnetic field or actively con- 

 strained to lie parallel to a uniform magnetic field, as shown in Figure 5. 



Paramagnetic and diamagnetic reactions of test samples in magnetic 

 fields are detectable, although feeble in comparison to the relatively strong 

 force with which the earth's magnetic field acts on a steel (ferromagnetic) 

 compass needle. Paramagnetic and diamagnetic characteristics of materials 

 are also, in a sense, relative. It has been observed that if a substance is 

 less magnetic that the medium surrounding it, it acts as a diamagnetic 

 substance. For example, a ferric chloride solution (FcoCle) is magnetic. 

 A capsule filled with such a solution, if placed in a basin containing ferric 

 chloride of a higher concentration (and hence more magnetic than the 

 solution in the capsule) will act as though it were diamagnetic. If, however, 

 the same capsule is placed in a basin of distilled water or of weaker ferric 

 chloride solution, it will align itself with the force lines of a magnetic field 

 and react as a magnetic substance. 



Geomagnetically this experiment is significant. In northern Michigan, 

 certain diabase dikes act as lenticular diamagnetic bodies, because of the 



