USE OF RENORMALIZATION-GROUP THEORY TO EXPLAIN THE LARGE VARIATION OFDOMAIN STATES OBSERVED IN TITANOMAGNETITES AND IMPLICATIONS FOR PALEOMAGNETISM

Important experiments by Halgedahl (1991) demonstrate that a material can reach dramatically different domain states on cooling when the exp eriment is repeated many times. Renormalization group theory is applie d to show that small thermal fluctuations close to the magnetic orderi ng temperature produce ''predomain'' structures. These predomain struc tures usually vary from one experiment to the next, even when the expe rimental conditions do not change. On cooling, these predomain structu res are primarily responsible for determining the final domain states. Transdomain processes also occur during cooling, but these processes appear to be less important. Theory is presented to show that domain o bservations might be very useful to discriminate between primary therm al remanent magnetization and many forms of secondary magnetizations. In particular, a grain growth chemical remanent magnetization on the a verage will be characterized by a narrower distribution of magnetic do mains in a given size grain than that associated with a thermal remane nt magnetization.