Studies of the magnetic axis switching in magnetite

The influence of the external magnetic field on magnetic and crystallographic structure of magnetite was studied. We have confirmed, by means of vibrating sample magnetometer measurements, that external magnetic field can switch the easy magnetic axis to the new crystallographic direction. We have also proved by the direct observation of the crystalline structure that this phenomenon is strictly related to the crystallographic structure relaxation

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

Magnetite Fe 3

In the paper the influence of magnetic as well as electron-lattice interactions on the Verwey transition in magnetite related compounds is discussed based on the authors' experimental activity and available literature. While magnetism was proved to only reflect the transition, the results of nuclear inelastic scattering show that lattice dynamics actively participates in it. The studies of diffuse neutron scattering and heat capacity suggest also that the low temperature lattice properties of slightly doped magnetite are distinct from those with higher dopant concentration. Finally, recent theoretical results strongly suggest that the Verwey transition in magnetite cannot be understood and described without strong involvement of electron-lattice interactions

Magnetite Fe3\text{}_{3}O4\text{}_{4}: the Correlated Electron-Phonon System

In the paper the influence of magnetic as well as electron-lattice interactions on the Verwey transition in magnetite related compounds is discussed based on the authors' experimental activity and available literature. While magnetism was proved to only reflect the transition, the results of nuclear inelastic scattering show that lattice dynamics actively participates in it. The studies of diffuse neutron scattering and heat capacity suggest also that the low temperature lattice properties of slightly doped magnetite are distinct from those with higher dopant concentration. Finally, recent theoretical results strongly suggest that the Verwey transition in magnetite cannot be understood and described without strong involvement of electron-lattice interactions

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

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

Inter- and Intragrain Magnetization of Thallium-Based Superconductors

We report on magnetization and magnetic hysteresis measurements for the (Tl$\text{}_{0.6}$Bi$\text{}_{0.5}$)(Sr$\text{}_{0.9}$Ba$\text{}_{0.1}$)$\text{}_{2}$Ca$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{y}$ Ag-sheathed superconducting tape as well as for the powdered and bulk (Tl$\text{}_{0.6}$Pb$\text{}_{0.5}$)(Sr$\text{}_{0.9}$Ba$\text{}_{0.1}$)$\text{}_{2}$Ca$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{y}$ superconductors. For the investigated tape and bulk specimens the low field magnetization showed a deviation from the ideal linear M(H) dependence, which was attributed to the superposition of inter- and intragrain superconducting currents. Fitting of the theoretical magnetization curves to the experimental data allowed for the independent determination of the intragrain critical current densities for the superconducting grains and intergrain critical current densities for the weak link system at 77K

Supercritical extraction of plant material with carbon dioxide. Scaling up from laboratory to 1/4 technical scale

Na podstawie wyników ekstrakcji nadkrytycznej za pomocą CO2 wykonanej w skali laboratoryjnej dla wsadu wynoszącego ok. 100 g, prowadzonej pod ciśnieniem 20 MPa, wyznaczono najkorzystniejsze temperatury procesu i potwierdzono zasadność dodawania w trakcie procesu rozpuszczalnika organicznego. Uzyskane wyniki wykorzystano przy powiększaniu skali procesu i wykonaniu ekstrakcji wsadu o wadze ok. 5 kg w aparaturze % technicznej pod ciśnieniem 25 MPa. Ekstrakcji poddawano dwa znacznie różniące się surowce roślinne: makuchy lniane i liście zielonej herbaty.Yelocity and yield of the extraction of linseed cake and leafs of green tea with supercritical carbon dioxide were tested. Initially both processes were tested in the laboratory scalę (150 cm3) under pressure of 20 MPa, using a dried and grinded plant feed (90-140 g). The influence of an entrainer was also tested. Optimized conditions such as temperaturę were used in scaling up the extraction. The !/4 scalę process was carried out in the extractor of 10 dm3 volume and under pressure of 25 MPa. Results achieved in the large scalę experiments confirmed conclusions from the laboratory experiments

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