Paleomagnetism and nonlinear magnetization processes in rocks
Paleomagnetism and nonlinear magnetization processes in rocks
V.I. Trukhin, 0.L. Bagina, V.A. Zhilyaeva, V.Yu. Safroshkin
It is shown that Fe-Ti oxides of rocks undergo complex evolution in the course of geologic time which affects their magnetic properties. In some cases there is a nonlinear relationship between natural remanent magnetization and geomagnetic field $H_g$ resulting from strong internal interaction in multiphase ferrimagnetic minerals, including those that determine the self-reversal of their magnetization. Consideration for nonlinear magnetization processes in rocks is required to increase the accuracy of paleomagnetic data.
Show AbstractThe effect of atomic volume on exchange interaction integrals in R-Fe amorphous alloys and crystalline compounds
The effect of atomic volume on exchange interaction integrals in R-Fe amorphous alloys and crystalline compounds
A.S. Andreenko, S.A. Nikitin, Yu.I. Spichkin
Magnetization and magnetic susceptibility under applied hydrostatic pressures of up to 10 kbar were studied for R-Fe amorphous alloys and crystalline compounds, where R is a heavy rare-earth metal. The results are discussed in terms of the molecular field theory. The difference in exchange integral versus applied pressure relationships between R-Fe amorphous alloys and crystalline compounds are explained by the difference in the short-range order. Hydrostatic pressure induces a noncollinear magnetic structure in $Y_2Fe_{17}$ and $Er_2Fe_{17}$ crystals and transforms two paramagnetism-asperomagnetism-reversible spin-glass phase transitions into a single paramagnetism-spin-glass phase transition in the amorphous $Y_{19}Fe_{81}$ alloy. This is explained by a reversal of the ratio between the positive and negative exchange interactions within the iron subsystem.
Show AbstractSpecific features of magnetic and magnetoelastic properties of Jahn-Teller magnets
Specific features of magnetic and magnetoelastic properties of Jahn-Teller magnets
V.I. Sokolov, Z.A. Kazei
Magnetic and magnetoelastic properties of a series of rare-earth zircons exhibiting the cooperative Jahn-Teller (JT) effect have been systematically studied. Typical anomalies of magnetic susceptibility, magnetization, and magnetic anisotropy in the basal plane have been observed, which are caused by the JT interaction and the cooperative JT effect. It is shown that the magnetoelastic properties of rare-earth zircons become much more pronounced due to JT correlations. The behavior of these characteristics in crystals differs qualitatively depending on whether the JT correlations are suppressed or enhanced by the magnetic field.
Show AbstractA study of spin-reorientation transitions in rare-earth orthoferrites and orthochromites
A study of spin-reorientation transitions in rare-earth orthoferrites and orthochromites
A.M. Kadomtseva, I.B. Krynetskii, D.V. Belov, V.N. Milov, Yu.F. Popov
Magnetization, magnetostriction, rotation moments, thermal expansion, Young's modulus, and internal friction were measured in rare-earth orthoferrites (orthochromites) to study spontaneous and induced magnetic phase transitions in them. The measurements were conducted in fields not exceeding 60 kOe, in the 1.7-140 K temperature range. New orientation phase transitions are found, experimental phase (H, T)-diagrams are constructed, and microscopic mechanisms of the phase transitions are discussed.
Show AbstractMagnetoelectric effects in terbium and gadolinium molybdates
Magnetoelectric effects in terbium and gadolinium molybdates
B.K. Ponomarev, S.A. Ivanov, B.S. Red'kin, V.N. Kurlov
The effect of a magnetic field H<110 kOe on the electric polarization of single-crystal samples of metastable ferroelectric rare-earth metal molybdates $Тb_1(МоO_4)_3, Gd_2(MoO_4)_3$, and $TbGd(MoO_4 )_3$ was studied at 78 K. The experiments showed that at 78 K the applied magnetic field changes the electric polarization and the ferroelectric domain structure of $TbGd(MoO_4)_3$ and $Tb_2(MoO_4)_3$. Effects of two types were observed: a) a magnetic field-induced deflection of the spontaneous polarization vector from its equilibrium orientation (rotation processes), and b) a field-induced nucleation and growth of domains with opposite electric polarization directions in initially single-domain samples (displacement processes). It is most likely that the observed effects are related to the properties of rare-earth metal ions.
Show AbstractMagnetic properties and kinetic effects in manganites with a narrow forbidden zone
Magnetic properties and kinetic effects in manganites with a narrow forbidden zone
E.P. Svirina, L.P. Shlyakhina
The results of a comprehensive investigation of magnetic and electric properties of $LaMnO_3$-based magnetic semiconductors with Mn ions replaced by ions of 3d metals (Fe, Co, and Ni) are presented. Also discussed are the available literature data on manganites with variously replaced La and Mn ions. The conclusion is drawn that the manganites studied are magnetic semiconductors with a narrow forbidden zone, whose magnitude is comparable with that of the exchange interaction energy. It is shown that the effect of the exchange energy on the structure of energy bands of current carriers results in (a) a correlation of the magnetic and electric properties, (b) anomalous behavior of kinetic effects, (c) a metal-semiconductor transition in the ferromagnetic region at a given temperature upon variation of the composition, and (d) a metal-semiconductor transition in the region of the Curie point.
Show AbstractOn low-temperature phase transitions in the $CoFe_2O_4$ and $MnFe_2O_4$ spinel ferrites
On low-temperature phase transitions in the $CoFe_2O_4$ and $MnFe_2O_4$ spinel ferrites
K.P. Belov, A.N. Goryaga
The data obtained in the studies on the temperature dependences of magnetization, magnetostriction, thermal expansion, magnetic anisotropy constant, and magnetoresistance for the $CoFe_2O_4$ and $MnFe_2O_4$ spinel ferrites are presented. The curves display anomalous behavior (maxima, inflections, etc.) below the Curie temperatures. The data suggest that ferrites with the spine! structure have several low-temperature structural and magnetic phase transitions. By low-temperature phase transitions we mean phase transitions at temperatures below the Curie point.
Show AbstractOn the mechanism of intersublattice exchange in intermetallic compounds of rare-earth metals and iron
On the mechanism of intersublattice exchange in intermetallic compounds of rare-earth metals and iron
A.K. Kupriyanov, V.A. Vasil'kovskii, V.F. Ostrovskii
Shifts of hyperfine fields are measured by the method of spin echo on the nuclei of gadolinium and yttrium in quasi-binary and ternary Laves phases containing impurity atoms of terbium and samarium. The analysis of the results obtained suggests the presence of negative 5d polarization in the neighborhood of gadolinium atoms. A new mechanism of intersublattice exchange, which is a version of hybrid exchange, is proposed.
Show AbstractThe nature of magnetic and anisotropic properties of yttrium iron garnets with substitutional Ce3+, $Sm^{3+}$, $Nd^{3+}$ and $Tm^{3+}$ ions
The nature of magnetic and anisotropic properties of yttrium iron garnets with substitutional Ce3+, $Sm^{3+}$, $Nd^{3+}$ and $Tm^{3+}$ ions
N.V. Volkova, L.A. Skipetrova
A great body of experimental data on the magnetic and anisotropic properties of yttrium iron garnets doped with $Ce^{3+}$, $Sm^{3+}$, $Nd^{3+}$, and $Tm^{3+}$ ions have been considered. The data obtained are compared with the available theoretical concepts concerning anisotropy and magnetostriction of ferrimagnetics. The possible nature of magnetic anisotropy in these compounds is suggested. It is shown that for all the ferrites studied, the magnetic anisotropy at small concentrations of rare-earth ions can be explained within the framework of the single-ion model, whereas at high concentrations the two-ion model must be used because the anisotropic exchange interaction between pairs of magnetic ions must be taken into account.
Show AbstractThree-gluon recombination of charmonium in quark-gluon plasma
Three-gluon recombination of charmonium in quark-gluon plasma
R.N. Faustov, I.G. Vasilevskaya
It is established that, when determining the relationship between the contributions from the various possible mechanisms of suppression of birth of $J/\Psi$ charmonium in collisions of heavy ions, it is necessary to consider, along with the $J/\Psi$ dissociatiqn in the quark-gluon plasma, the competitive recombination process $3g \to J/\Psi$ of the three-gluon annihilation.
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