This work is testing a new empirical scaling law showing that the efficiency of acquisition of Thermal Remanent Magnetization (TRM) exhibits a power low field dependence, with offsets for different materials according to the saturation magnetization M(s) (Kletetschka et al. 2004). The most remarkable aspect of the new results is that the law holds over the range of domain states from single domain to multidomain for titanomagnetite. Thus, although many of the initial samples were large and multidomain, the results from magnetite suggest that the law may have universal application.
The first key problem in investigating the scaling law in rocks is the nature of the demagnetizing factor (N) of distributions of particles in synthetic samples and rocks. N is most often encountered in discussions of weak field susceptibility, where the apparent susceptibility can be strongly controlled by demagnetizing effects.
Because the demagnetizing factor is such an important part of the acquisition process, TRM and IRM in distributions of particles is being determined in rocks whosedemagnetizing factors are known. The key observations that are required are to test the power law for well-controlled distributions of fine particles whose demagnetization factors are known. Given the sensitivity of modern magnetometers, this can be done using relatively small and controllable number of particles. They will be examined microscopically and dispersed in high temperature cement and "slides" prepared. Initially, interactions are being avoided, but eventually distribution with interactions will be generated. The dispersions are being aligned using strong magnetic fields, relative to which the sample can be kept stationary or rotated. The final synthetic samples are then reexamined with optical and scanning electron microscopy. ARM and TRM are then being given in a variety of fields and the analysis by IRMs normalization carried out.
Comparison of the paleointensity estimates from IRMs normalization is done with classical standard double heating methods for the synthetic samples and the major collection of rocks available. Our results show possible uses of the IRMs normalization method and provide motivation to delve deeper in to the topic of the fundamental law that the analyses are based upon. The NRM, ARM, v IRMs plots are by no means the only means of selection of samples for suitability for paleointensity observations. However, they are quite simply obtained data and easy to read.
Thermoremanent Magnetization (TRM) is one of the most important carriers of the paleomagnetic record and therefore to develop a convincing model of it has ramifications for geophysics and planetary physics. Such a simple empirical law describing the efficiency of acquisition of TRM is very remarkable. One of the most intriguing results in lunar magnetism came from an application of this idea and other possible applications in the magnetism of meteorites hold major promise.
This work is in an excellent research area for undergraduate work. There are measurements of a relatively routine kind, so that they are not overwhelmed by the necessary laboratory techniques. Yet students learn that the measurements must be made carefully. Students also eventually learn plenty of basic laboratory techniques and some practical electromagnetism.
