An Experimental Demonstration of the Production of Chemical Remanent Magnetization with Cu-Co Alloy

Abstract

Magnetization-blocking process in chemical remanent magnetization was demonstrated through the size development of ferromagnetic precipitates generated by an aging of Cu-Co alloy, the magnetic behaviour of which changes from superparamagnetic to stable single domain and then to multidomain one, according to the increase in the size of the precipitates. It has been shown that a remanent magnetization is acquired during the transition from a superparamagnetic to stable ferromagnetic state and that the remanent magnetization thus obtained decreases as a result of the formation of domain walls if the size of the precipitates exceeds the critical single domain grain size. The result can be well explained by Neel's thermal fluctuation theory of single domain grains and the domain structure theory of ferromagnetics. The particle sizes at various stages of aging were estimated by different granulometry methods with roughly consistent results. The general idea confirmed in the present study has been successfully extended to the CRM phenomena in synthetic and natural ferromagnetic minerals. It was suggested that specimens produced by low temperature chemical changes can be classified into four groups, i.e. the superparamagnetic stage, magnetically-stable single domain stage, the transient stage from single domain to multidomain structure and the perfectly developed multidomain stage from the view-point of the nucleation of ferromagnetic minerals. The magnetic behaviour of several specimens already reported can be consistently interpreted on the basis of the present experiment.