Magnetic Clusters in Natural Ferro-Chromian Spinels

The results of investigations of natural iron-chromium spinels of variable composition Fe2+(Cr2-xFex3+)O4 of the chromite-bearing Klyuchevskoi massif (Middle Urals), which are the main carriers of the magnetization of rocks are presented. Substantial changes in the composition and in magnetic structure of accessory chrome-spinels scattered in the host rock are established, unlike the almost unaltered ore-forming chrome-spinels, under the influence of secondary geological processes. To establish the connection between the chrome-spinel changes at the microlevel and features of the geomagnetic field anomalies created by this carrier of magnetization of rocks, it is carried out a complex of investigations of Fe-Cr-spinels (thermomagnetic analysis over the temperature range (4÷1000) K; magnetic resonance (MR) spectroscopy and magnetic force microscopy (MFM) in addition to magnetomineralogical studies). As a result, in the relict areas of grains of the accessory chrome-spinels were first discovered the magnetic clusters (superparamagnetic phases) in the form of single or groups of 2 – 3 magnetic dipoles of tens nanometers in size, or in the form of chain-like structures of magnetic dipoles/single domains.