Information loss due to thermal activation is a major concern in ultrahigh-density magnetic recording media. The usually considered mechanism is thermally activated magnetization reversal over micromagnetic energy barriers. However, micromagnetic approaches ignore local anisotropy fluctuations, which translate into a time-dependent reduction of the remanent magnetization. The effect is negligib...

Monte Carlo simulations of diluted Ising-type antiferromagnets in a uniform external magnetic field in three dimensions show rather strong irreversibilities in the magnetization and a slow relaxation of the remanent magnetization of the domain state. A detailed investigation of the domain state and its relaxation shows that for low temperatures domains are strongly pinned at vacancies and that ...

Although recent studies have revealed more widespread occurrences of magnetofossils in pre-Quaternary sediments than have been previously reported, their significance for paleomagnetic and paleoenvironmental studies is not fully understood. We present a paleo- and rock-magnetic study of late Miocene marine sediments recovered from the Guadalquivir Basin (SW Spain). Well-defined paleomagnetic di...

Introduction: The aggregational texture and bulk chemical composition of chondrites demonstrate that they are not the products of planetary melting proceses. As a result, chondrites have traditionally been thought to samples bodies that have not undergone large-scale differentiation [1]. However, it has long been known that CV and other carbonaceous chondrites carry a stable natural remanent ma...

Andesitic pumice erupted in 1985 from Nevado del Ruiz volcano (Colombia) has been magnetized in opposite direction t o the present geomagnetic field. This self-reversal is probably due t o an exchange mechanism between two phases of the haematite-ilmenite series, which is similar to the magnetic coupling observed in synthetically grown antiferromagnetic-ferromagnetic FeMn-FeNi films produced un...