Verwey transition in Fe3_{3}O4_{4} at high pressure: quantum critical behavior at the onset of metallization

We provide evidence for the existence of a {\em quantum critical point} at the metallization of magnetite Fe$_{3}$O$_{4}$ at an applied pressure of $p_{c} \approx 8$ GPa. We show that the present ac magnetic susceptibility data support earlier resistivity data. The Verwey temperature scales with pressure $T_{V}\sim (1-p/p_{c})^{\nu}$, with $\nu\sim 1/3$. The resistivity data shows a temperature dependence $\rho(T)=\rho_{0}+AT^{n}$, with $n\simeq 3$ above and 2.5 at the critical pressure, respectively. This difference in $n$ with pressure is a sign of critical behavior at $p_{c}$. The magnetic susceptibility is smooth near the critical pressure, both at the Verwey transition and near the ferroelectric anomaly. A comparison with the critical behavior observed in the Mott-Hubbard and related systems is made.Comment: 5 pages, 5 figure

On topological properties of Fréchet locally convex spaces

[EN] We describe the topology of any cosmic space and any N-o-space in terms of special bases defined by partially ordered sets. Using this description we show that a Baire cosmic group is metrizable. Next, we study those locally convex spaces (lcs) E which under the weak topology sigma(E, E') are N-o-spaces. For a metrizable and complete lcs E not containing (an isomorphic copy of) l(1) and satisfying the Heinrich density condition we prove that (E, sigma(E,E')) is an N-o-space if and only if the strong dual of E is separable. In particular, if a Banach space E does not contain l(1), then (E, sigma(E, E')) is an N-o-space if and only if E' is separable. The last part of the paper studies the question: Which spaces (E, sigma(E, E')) are N-o-spaces? We extend, among the others, Michael's results by showing: If E is a metrizable lcs or a (DF)-space whose strong dual E' is separable, then (E, sigma(E, E')) is an N-o-space. Supplementing an old result of Corson we show that, for a Cech-complete Lindelof space X the following are equivalent: (a) X is Polish, (b) C-c(X) is cosmic in the weak topology, (c) the weak*-dual of C-c(X) is an N-o-space.The second and fourth named authors were supported by Generalitat Valenciana, Conselleria d'Educacio, Cultura i Esport, Spain, Grant PROMETEO/2013/058.Gabriyelyan, S.; Kakol, JM.; Kubzdela, A.; López Pellicer, M. (2015). On topological properties of Fréchet locally convex spaces. Topology and its Applications. 192(1):123-137. https://doi.org/10.1016/j.topol.2015.05.075S123137192

Influence of chosen habitable agents on planting tendril willow Salix viminalis in mountain conditions

W opracowaniu przedstawiono aspekty siedliskowe upraw wierzby wiciowej w warunkach górskich. Na podstawie badań własnych i stosownej literatury, uzasadniono, że mimo mało sprzyjających czynników siedlisk górskich, do produkcji roślinnej, celowa jest dalsza uprawa roli, aby utrzymać glebę w dobrej kulturze i zahamować rozprzestrzenianie się wieloletnich chwastów na odłogowanych polach. Uwzględnienie i osłabienie wpływu niekorzystnych czynników siedliska, poprzez odpowiedni dobór roślin, na przykład optymalnych dla tych warunków klonów wierzby oraz stosowanie przy jej uprawie i zbiorze właściwych zabiegów agrotechnicznych, może mieć pozytywne skutki ekologiczne, ekonomiczne i społeczne dla mieszkańców gmin górskich.Study presents habitable aspects of cultivation tendril willow in mountain conditions. On the basis of personal research and suitable literatures justified, that in spite of weak agents of mountain habitations for vegetable production, it is necessary to continue cultivation of mountain lands to keep this land in good condition and stop the spreading of perennial weed on uncultivated land in mountain villages. Taking into consideration and reduction of influence of unfavorable agents of habitation, by the proper selection of plants, for example using the appropriate clones of willow for this conditions and specific agro technical procedures, during raising and harvesting, it could leads to positive ecological, economic and social results on inhabitants of mountain villages

Cation Distribution in Fe3(1−δ)\text{}_{3(1-\delta)}O4\text{}_{4} and Low Level Doped Fe3−x\text{}_{3-x}Mx\text{}_{x}O4\text{}_{4}, M=Ti, Zn, Al

Systematic magnetic saturation moment and electrical resistivity measurements of the Fe$\text{}_{3(1-\delta)}$O$\text{}_{4}$ and Fe$\text{}_{3-x}$M$\text{}_{x}$O$\text{}_{4}$ (M = Ti, Zn, Al) are presented. Cation distributions for low level doping are proposed and compositional dependencies of the Verwey transition temperature are determined. The latter show striking similarities in their dependence on cation vacancies and dopant concentration for any extraneous cations. These data are the basis for the analysis of the correlation between the presented cations distributions and the Verwey transition

Rhombohedral Distortion in Fe3−y\text{}_{3-y}Zny\text{}_{y}O4\text{}_{4} at Verwey Transition

The time-of-flight neutron diffraction data were collected for two Fe$\text{}_{3-y}$Zn$\text{}_{y}$O$\text{}_{4}$ powder samples showing different order of the Verwey transition: y=0.0072 - first order, y=0.0249 - second order. Measurements were performed on spallation neutron source in ISIS Rutherford Appleton Laboratory. At low temperatures (below Verwey transition temperature T$\text{}_{V}$) clear splitting of certain reflections characteristic of rhombohedral distortion was observed for both samples. We found that this distortion is much bigger for the sample exhibiting first-order than for the sample showing second-order transition

Studies of magnetic axis switching phenomenon in magnetite

Abstract The results of magnetic and structural studies of magnetic easy axis switching in magnetite are presented. This phenomenon was first observed after the easy axis was established by the in-field cooling across the Verwey transition. Although the subsequent application of magnetic field at low temperatures along certain <1 0 0> is almost as effective in establishing the easy axis as field cooling, the repeated easy axis redirection below T V causes the field required to switch the axis to become lower. We have also shown that the change of magnetic easy axis is reflected in the change of crystallographic c direction. Finally, the energy required to switch the axis was calculated and was found comparable to the characteristic energy of the Verwey transition

Photoemission electronic states of epitaxially grown magnetite films

Abstract The valence band photoemission spectra of epitaxially grown 300Á single crystalline magnetite films were measured by the angle-resolved ultraviolet photoemission spectroscopy (ARUPS) at 300 K. The samples were grown either on MgO(0 0 1) (B termination) or on (0 0 1) Fe (iron-rich A termination), thus intentionally presenting different surface stoichiometry, i.e. also different surface electronic states. Four main features of the electron photoemission at about −1.0, −3.0, −5.5 and −10.0 eV below a chemical potential show systematic differences for two terminations; this difference depends on the electron outgoing angle. Our studies confirm sensitivity of angle resolved PES technique on subtleties of surface states

Magnetic and structural studies of magnetite at the Verwey transition

Abstract Studies of the Verwey transition in zinc doped magnetite (Fe 3−x Zn x O 4 , x = 0, 0.0097, 0.011, 0.036) by simultaneous ac magnetic susceptibility (χ) and electric resistance measurements are presented. The temperature hysteresis of the Verwey transition increases from 0.03 K for stoichiometric magnetite to 0.5 K for Zn doped samples, despite the continuous character of the transition. The results of introductory observations of structural changes are also presented

Magnetic AC susceptibility of stoichiometric and low zinc doped magnetite single crystals

Systematic studies of AC susceptibility in a stoichiometric magnetite single crystal, in a series of low zinc doped magnetite ($x_{\rm Zn} < 0.04$) and in nonstoichiometric magnetite samples (both single crystals and pellets) in the temperature range 4–300 K are presented. Measurements were performed in several AC fields ($H_{AC}=0.2{-}20\$Oe) and at different frequencies (15–6000 Hz). It is suggested that the signal is primarily due to magnetic domain wall movement, strongly influenced by structural domains (twins). Two sets of anomalies were found: the first is associated with the Verwey transition and the second involves two different effects, one at 28 K, observed only in stoichiometric magnetite, and the other at 50 K. While the temperature position of the first anomaly (28 K) does not depend on frequency, the effect at 50 K is associated with an activation process, shifting to higher temperatures with increasing frequency. This last effect may be linked to the low temperature magnetoelectric effects terminating approximately at those temperatures. Qualitatively similar results have been observed by the Magnetic After Effect technique presented in the literature, that is associated with relaxation times that are 104 higher than those characteristic of our technique