Аннотация:Paleomagnetic research of rocks earth crust show that the reverse magnetization of ferromagnetic minerals occur as
often as the direct magnetization. One possible reason is the reverse magnetization occurred in the past geomagnetic
field inversions. There is an alternative theory of magnetization rock opposite to the direction of the geomagnetic
field, - reversal of magnetization, which may occur either during cooling ferrimagnetic or by oxidation during the
succeeding life of rock geology.
Possible mechanisms of inverse magnetization were considered theoretically L. Neel [1]. For single-phase ferrimagnetics
they were offered several options for behavior of the temperature dependence of the spontaneous
magnetization, which is the sum of the magnetizations of the two sublattices oppositely directed a change in temperature
can vary from positive to negative values ??associated with different temperature variation of spontaneous
sublattice magnetizations.
Neel mechanism self-reversal supposes the compensation point. Ferrimagnetic minerals (1-x) Fe3O4xMg2TiO4,
the most common arrays alkaline ultrabasic rocks and carbonatites have a spinel structure in which
metal cations occupy octahedral and tetrahedral sites. According to the most probable distribution of
Fe3+[Mg2xTixFe2+
1����xFe3+
1����2x]O4 for compositions x<0.3 according to the Neel’s theory can calculate the value
of «x», in which the magnetic moments of saturation of the sublattices are equal and therefore compensated. This
value is x = 0.286 [2].
Chromospinelide series (1-x) Fe2CrO4 xFeCrMgO4 compose a number of types of chromite deposits. They are
the bearers of rock magnetization some kimberlite pipes are widely distributed in deep gabbro and peridotite, and
lunar rocks and meteorites. On the proposed cation distribution - Fe3+[Fe2+
1����xMgxCr]O4 magnetic moments of the
sublattices be compensated for the composition Fe1:5Mg0:5CrO4 (x=0.5) [2].
The magnetic properties of the synthesized minerals above series of experimental data show an
incompatibility with the alleged theoretical concepts according ferrimagnetism Neel. For chromespinelides
Fe2CrO4 - FeCrMgO4 depending on s (x) minimum is observed spontaneous magnetization at x = 0.7, indicating
that the proximity of this composition to composition with compensated ferrimagnetic sublattices [3]. Compositional
dependence of s(x) for magnesian titanomagnetite Fe3O4 - Mg2TiO4 shows a linear decrease of the
spontaneous magnetization of the composition, i.e. for this series sublattice compensation absent [4].
At the same time, self-reversal of magnetization for some compositions presented a series of spinels observed after
heating to 6000C ferrites in the air. Self-reversal of thermoremanent magnetization chromespinelides explained the
formation of a gradient in the distribution of metal cations, which occurs when a single-phase oxidation of minerals
[3]. In magnesia titanomagnetites is due to the self- spin exchange interaction decay phases - hemoilmenites
magnesia having a different degree of ordering of the ions [4].
In natural minerals rather characterized by the presence of inhomogeneities caused by the phase transformation
occurring for a long time. Consequently, self-reversal on the proposed mechanisms is quite possible for natural
minerals and can occur at any stage of life rock.
1. Néel L. Propriétés magnétiques des ferrites: ferrimagnétisme et antiferromagnétisme // Ann. Phys. 1948. V. 3,
N 2. P.137–198.
2. Kudryavtseva G.P., Ferrimagnetizm of Natural Oxides // Moscow, 1988 [in Russian].
3. Maksimochkin V.I., Gubaidullin R.R., Gareeva M.Ya. Magnetic properties and structure of Fe2����xMgxCrO4
chromites // Moscow University Physics Bulletin 2013. V 68, N 3, pp 241-248
4. Bugaev M.S., Zverintsev A.G., Belobrova I.A. Magnetization self-reversal in magnesian titanomagnetites // Izv.
AN SSSR. Ser. Fizika Zemli 1972. N 5. 53.
The work was supported by the Russian Foundation for Basic Research (projects no. 13-05-00514).