Magnon Bose condensation in symmetry breaking magnetic field

Magnon Bose condensation (BC)in the symmetry breaking magnetic field is a result of unusual form of the Zeeman energy, which has terms linear in the spin-wave operators and terms mixing excitations differ in the Wave-vector of the magnetic structure. The following examples are considered: simple easy-plane tetragonal antiferromagnets (AF), frustrated AF family$R_2Cu O_4$ where $R=Pr,Nd$ etc. and cubic magnets with the Dzyaloshinskii-Moriya interaction ($Mn Si$ etc.). In all cases the BC becomes important when the magnetic field becomes comparable with the spin-wave gap. The theory is illustrated by existing experimental results.Comment: Submitted to J. of Phys. Condens. Matter (Proceedings of International Conference "Highly Frustrated Magnets", Osaka (Japan), August 2006). 8 pages, 5 figure

Chiral criticality in doped Mn1−y_{1-y}Fey_ySi compounds

The critical spin fluctuations in doped compounds Mn$_{1-y}$Fe$_y$Si have been studied by means of ac-susceptibility measurements, polarized neutron small angle scattering and spin echo spectroscopy. It is shown that these compounds undergo the transition from the paramagnetic to helimagnetic phase through continuous, yet well distinguishable crossovers: (i) from paramagnetic to partially chiral, (ii) from partially chiral to highly chiral fluctuating state. The crossover points are identified on the basis of combined analysis of the temperature dependence of ac-susceptibility and polarized SANS data. The whole transition is marked by two inflection point of the temperature dependence of ac-susceptibility: the upper one corresponds to the crossover to partially chiral state at $T^*$, where the inverse correlation length $\kappa \approx 2 k$, the lower one corresponds to the transition to the spin helix structure. The intermediate crossover to the highly chiral phase is observed at the inflection point $T_k$ of the first derivative of ac-susceptibility, where $\kappa \approx k$. The temperature crossovers to the highly chiral fluctuating state is associated with the enhancing influence of the Dzyaloshinskii-Moria interaction close to $T_c$.Comment: 5 pages, 5 figures, 1 table, 13 cite

Magneto-elastic interaction in cubic helimagnets with B20 structure

The magneto-elastic interaction in cubic helimagnets with B20 symmetry is considered. It is shown that this interaction is responsible for negative contribution to the square of the spin-wave gap $\Delta$ which is alone has to disrupt assumed helical structure. It is suggested that competition between positive part of $\Delta^2_I$ which stems from magnon-magnon interaction and its negative magneto-elastic part leads to the quantum phase transition observed at high pressure in $Mn Si$ and $Fe Ge$. This transition has to occur when $\Delta^2=0$. For $Mn Si$ from rough estimations at ambient pressure both parts $\Delta_I$ and $|\Delta_{ME}|$ are comparable with the experimentally observed gap. The magneto-elastic interaction is responsible also for 2\m k modulation of the lattice where \m k is the helix wave-vector and contribution to the magnetic anisotropy. Experimental observation by $x$-ray and neutron scattering the lattice modulation allows determine the strength of anisotropic part of the magneto-elastic interaction responsible for above phenomena and the lattice helicity

An Electron Spin Resonance Selection Rule for Spin-Gapped Systems

The direct electron spin resonance (ESR) absorption between a singlet ground state and the triplet excited states of spin gap systems is investigated. Such an absorption, which is forbidden by the conservation of the total spin quantum number in isotropic Hamiltonians, is allowed by the Dzyaloshinskii-Moriya interaction. We show a selection rule in the presence of this interaction, using the exact numerical diagonalization of the finite cluster of the quasi-one-dimensional bond-alternating spin system. The selection rule is also modified into a suitable form in order to interpret recent experimental results on CuGeO$_3$ and NaV$_2$O$_5$.Comment: 5 pages, Revtex, with 6 eps figures, to appear in J. Phys. Soc. Jpn. Vol. 69 No. 11 (2000

Spin chirality induced by the Dzyaloshinskii-Moriya interaction and the polarized neutron scattering

We discuss the influence of the Dzyaloshinskii-Moriya (DM) interaction in the Heizenberg spin chain model for the observables in the polarized neutron scattering experiments. We show that different choices of the parameters of DM interaction may leave the spectrum of the problem unchanged, while the observable spin-spin correlation functions may differ qualitatively. Particularly, for the uniform DM interaction one has the incommensurate fluctuations and polarization-dependent neutron scattering in the paramagnetic phase. We sketch the possible generalization of our treatment to higher dimensions.Comment: 4 pages, REVTEX, no figures, references added, to appear in PR

Role of domain wall fluctuations in non-Fermi liquid behavior of metamagnets

We study resistivity temperature dependence of a three dimensional metamagnet near the metamagnet phase transition point in the case when magnetic structure tends to split into regions with high and low magnetization. We show that in the case of weak pinning the spin relaxation time of domain wall is much larger than that of the volume spin fluctuations. This opens a temperature range where resistivity temperature dependence is determined by scattering of conducting electrons by the domain wall fluctuations. We show that it leads to quasi-linear low temperature dependence of resistivity

Гормонально-иммунологический статус и особенности питания у лиц с ожирением

Nourishment peculiarities of 120 patients aged from 41 years having excess body mass and obesity were investigated. Interre-lations with changed hormonal-immune status were assessed. Method of food taking rate developed in the Institute of Nourishment, RAMS, taking into account nourishing peculiarities of Russian population was used. Study results revealed, that patients had imbal-ance concerning main macro- and micronutrients: nourishment regimen was disturbed in 90% of cases, taking main part of energy value was shifted to the second half of a day, increased calorie content of nourishment, excess of monosaccharides in the setting of decreased physical activity were seen which plays the main role in the development and advancing obesity, increased level of leuco-cytes, of TNF-α, IFN-γ, humoral immunity link imbalance, increased serum concentration of leptin and insulin which is closely cor-relates with excess body mass and nourishment peculiarities.Исследованы особенности питания 120 пациентов в возрасте от 18 до 41 года с избытком массы тела и ожирением. Оценены взаимосвязи с изменениями гормонально-иммунологического статуса. Применялся метод анализа частоты потребления пищи, разработанный в Институте питания РАМН с учетом особенностей питания населения России. По результатам исследования установлено, что у пациентов наблюдался дисбаланс по основным макро- и микронутриентам, примерно в 90% случаев нарушен режим питания, прием основной части энергетической ценности рациона смещен на вторую половину дня, отмечены рост общей калорийности питания, избыток моносахаридов, жиров на фоне прогрессирующего снижения физической активности, а значит и энергозатрат, что играет основную роль в развитии и прогрессировании ожирения, отмечается повышение уровня лейкоцитов, TNF-α, IFN-γ, дисбаланс гуморального звена иммунитета, повышение сывороточной концентрации лептина и инсулина, тесно коррелированное с ИМТ и особенностями питания