Electron microscopy, magnetoclimatology, archaeomagnetic secular variation

五十年来，地质和考古材料的磁性已被证明是有关地球历史和动态的丰富信息来源。南北磁极的转换（地磁极性反转），海底的形成和破坏以及由此导致的大陆漂移（板块构造），大冰盖的盛衰（过去的全球变暖和变冷）都是我们脑海中浮现的主要例子。然而，我们对导致捕获这些信号的基本物理机制的理解仍然存在严重的缺陷。其中一个棘手的问题是不同自然档案中单个磁性晶体之间的相互作用。这些使磁性变得如此复杂，以至于路易斯·纳姆泽尔（1970年诺贝尔物理学奖得主）在他的经典论文中明智地避免了这个问题，他考虑了一种微小的不相互作用的磁性粒子的稀释组合。不幸的是，我们感兴趣的矿物（铁钛氧化物）通常以纳米级的共生体的形式出现，其中磁性区域彼此靠近。最近的三个事态发展使我们有可能对这一问题进行新的努力。首先，电子显微镜现在能够提供感兴趣的样品内部磁场模式的详细图像。其次，现在大大提高的计算能力使得计算相互作用的磁性粒子阵列的行为成为可能。第三，新实验室技术的发展为相互作用的强度提供了直接的实验测量。除了这些矿物物理研究外，还将进行古气候和考古地磁调查。前者将涉及已经从世界各地几个地点收集的样本，并将试图阐明气候信息在自然沉积档案中被磁编码的机制。后者将涉及从伊比利亚和埃及的考古结构中收集的新样本，以便扩大早先在希腊和意大利开展的运动的地理覆盖范围。

For fifty years, the magnetic properties of geological and archaeological materials have proven to be a rich source of information concerning our planet's history and dynamics. The switching of the north and south magnetic poles (geomagnetic polarity reversals), the creation and destruction of the ocean floor and the resulting drift of the continents (plate tectonics), the waxing and waning of the great ice sheets (past global warming -- and cooling) are prime examples that spring to mind. And yet there remain serious shortcomings in our understanding of the basic physical mechanisms that lead to the capture of these signals. One of the knotty problems involved is that of interactions between the individual magnetic crystals in the various natural archives in question. These complicate the magnetic properties so much that in his classic papers Louis Néel (Nobel Prize in Physics 1970) wisely avoided this problem by considering a dilute assemblage of tiny non-interacting magnetic particles. Unfortunately, the minerals of interest (iron-titanium oxides) often occur as nanometre-scale intergrowths in which magnetic regions lie in close proximity to one another. Three recent developments make it possible to undertake a renewed attack on this problem. First, electron microscopy is now able to provide detailed images of the magnetic field pattern inside samples of interest. Second, vastly increased computing power now makes it possible to calculate the behaviour of arrays of interacting magnetic particles. Third, the development of new laboratory techniques provides a direct experimental measure of the strength of the interactions. In addition to these mineral physics studies, palaeoclimatic and archaeomagnetic investigations will also be carried out. The former will involve samples already collected from several sites around the world and will attempt to elucidate the mechanisms by which climatic information is magnetically encoded in natural sedimentary archives. The latter will involve new samples collected from archaeological structures in Iberia and Egypt in order to extend the geographic coverage of earlier campaigns in Greece and Italy.