Electric field effects on magnetotransport properties of multiferroic Py/YMnO3/Pt heterostructures

We report on the exchange bias between antiferromagnetic and ferroelectric hexagonal YMnO3 epitaxial thin films sandwiched between a metallic electrode (Pt) and a soft ferromagnetic layer (Py). Anisotropic magnetoresistance measurements are performed to monitor the presence of an exchange bias field. When the heteroestructure is biased by an electric field, it turns out that the exchange bias field is suppressed. We discuss the dependence of the observed effect on the amplitude and polarity of the electric field. Particular attention is devoted to the role of current leakage across the ferroelectric layer.Comment: Accepted for publication in Philosophical Magazine Letters (Special issue on multiferroics

Металографічний аналіз потенційних ділянок зародження руйнування зони термічного вливу низьковуглицевих сталей після лазерного зварювання

The work investigates the detection of dangerous areas of the zones of thermal impact on the basis of the research of welding joint structure formation after laser welding of low-carbon steels 09Mn2Si, 10CrNiCu, 10Mn2VNb. The complex of studies carried out showed that the welded joint is structurally divided into several zones. At the same time, metallographic analysis showed that in the zones of the welded joint there is a conglomerate of structures, which contains components characteristic both for metal in the cast state and for metal after accelerated cooling.Досліджено виявлення небезпечних ділянок зони термічного впливу на підставі дослідження формування структури зварного з'єднання після лазерного зварювання низьковуглецевих сталей 09Г2С, 10ХСНД, 10Г2ФБ. Проведений комплекс досліджень показав, що зварене з'єднання структурно розділити на кілька зон. При цьому, металографічний аналіз показав, що в зонах зварного з'єднання присутні конгломерат структур, який містить складові характерні як для металу в литому стані так і для металу після прискореного охолодження.Исследовано выявление опасных участков зоны термического влияния на основании исследования формирования структуры сварного соединения после лазерной сварки низкоуглеродистых сталей 09Г2С, 10ХСНД, 10Г2ФБ. Проведенный комплекс исследований показал, что сварное соединение структурно разделить на несколько зон. При этом, металлографический анализ показал, что в зонах сварного соединения присутствуют конгломерат структур, который содержит составляющие характерные как для металла в литом состоянии так и для металла после ускоренного охлаждения

Pressure dependence of the Shubnikov-de Haas oscillation pectrum of beta''-(BEDT-TTF)4(NH4)[Cr(C2O4)3].DMF

The Shubnikov-de Haas (SdH) oscillation spectra of the beta''-(BEDT-TTF)4(NH4)[Cr(C2O4)\_3].DMF organic metal have been studied in pulsed magnetic fields of up to either 36 T at ambient pressure or 50 T under hydrostatic pressures of up to 1 GPa. The ambient pressure SdH oscillation spectra can be accounted for by up to six fundamental frequencies which points to a rather complex Fermi surface (FS). A noticeable pressure-induced modification of the FS topology is evidenced since the number of frequencies observed in the spectra progressively decreases as the pressure increases. Above 0.8 GPa, only three compensated orbits are observed, as it is the case for several other isostructural salts of the same family at ambient pressure. Contrary to other organic metals, of which the FS can be regarded as a network of orbits, no frequency combinations are observed for the studied salt, likely due to high magnetic breakdown gap values or (and) high disorder level evidenced by Dingle temperatures as large as about 7 K.Comment: To be published in European Physical Journal

Slow oscillations of magnetoresistance in quasi-two-dimensional metals

Slow oscillations of the interlayer magnetoresistance observed in the layered organic metal $\beta$-(BEDT-TTF)$_2$IBr$_2$ are shown to originate from the slight warping of its Fermi surface rather than from independent small cyclotron orbits. Unlike the usual Shubnikov-de Haas effect, these oscillations are not affected by the temperature smearing of the Fermi distribution and can therefore become dominant at high enough temperatures. We suggest that the slow oscillations are a general feature of clean quasi-two-dimensional metals and discuss possible applications of the phenomenon.Comment: 11 pages, 3 figure

Indication for the coexistence of closed orbit and quantum interferometer with the same cross section in the organic metal (ET)4(H3O)[Fe(C2O4)3].C6H4Cl2: Persistence of SdH oscillations above 30 K

Shubnikov-de Haas (SdH) and de Haas-van Alphen (dHvA) oscillations spectra of the quasi-two dimensional charge transfer salt $\beta$"-(ET)$_4$(H$_3$O)[Fe(C$_2$O$_4$)$_3$]$\cdot$C$_6$H$_4$Cl$_2$ have been investigated in pulsed magnetic fields up to 54 T. The data reveal three basic frequencies F$_a$, F$_b$ and F$_{b - a}$, which can be interpreted on the basis of three compensated closed orbits at low temperature. However a very weak thermal damping of the Fourier component F$_b$, with the highest amplitude, is evidenced for SdH spectra above about 6 K. As a result, magnetoresistance oscillations are observed at temperatures higher than 30 K. This feature, which is not observed for dHvA oscillations, is in line with quantum interference, pointing to a Fermi surface reconstruction in this compound.Comment: published in Eur. Phys. J. B 71 203 (2009

Robust isothermal electric switching of interface magnetization: A route to voltage-controlled spintronics

Roughness-insensitive and electrically controllable magnetization at the (0001) surface of antiferromagnetic chromia is observed using magnetometry and spin-resolved photoemission measurements and explained by the interplay of surface termination and magnetic ordering. Further, this surface in placed in proximity with a ferromagnetic Co/Pd multilayer film. Exchange coupling across the interface between chromia and Co/Pd induces an electrically controllable exchange bias in the Co/Pd film, which enables a reversible isothermal (at room temperature) shift of the global magnetic hysteresis loop of the Co/Pd film along the magnetic field axis between negative and positive values. These results reveal the potential of magnetoelectric chromia for spintronic applications requiring non-volatile electric control of magnetization.Comment: Single PDF file: 27 pages, 6 figures; version of 12/30/09; submitted to Nature Material

Comparison of coherent and weakly incoherent transport models for the interlayer magnetoresistance of layered Fermi liquids

The interlayer magnetoresistance of layered metals in a tilted magnetic field is calculated for two distinct models for the interlayer transport. The first model involves coherent interlayer transport and makes use of results of semi-classical or Bloch-Boltzmann transport theory. The second model involves weakly incoherent interlayer transport where the electron is scattered many times within a layer before tunneling into the next layer. The results are relevant to the interpretation of experiments on angular-dependent magnetoresistance oscillations (AMRO) in quasi-one- and quasi-two-dimensional metals. We find that the dependence of the magnetoresistance on the direction of the magnetic field is identical for both models except when the field is almost parallel to the layers. An important implication of this result is that a three-dimensional Fermi surface is not necessary for the observation of the Yamaji and Danner oscillations seen in quasi-two- and quasi-one-dimensional metals, respectively. A universal expression is given for the dependence of the resistance at AMRO maxima and minima on the magnetic field and scattering time (and thus the temperature). We point out three distinctive features of coherent interlayer transport: (i) a beat frequency in the magnetic oscillations of quasi-two-dimensional systems, (ii) a peak in the angular-dependent magnetoresistance when the field is sufficiently large and parallel to the layers, and (iii) a crossover from a linear to a quadratic field dependence for the magnetoresistance when the field is parallel to the layers. Properties (i) and (ii) are compared with published experimental data for a range of quasi-two-dimensional organic metals and for Sr2RuO4.Comment: 21 pages, RevTeX + epsf, 4 figures. Published version. Subsection added. References update

Reversible Control of Magnetic Interactions by Electric Field in a Single Phase Material

Intrinsic magnetoelectric coupling describes the interaction between magnetic and electric polarization through an inherent microscopic mechanism in a single phase material. This phenomenon has the potential to control the magnetic state of a material with an electric field, an enticing prospect for device engineering. We demonstrate 'giant' magnetoelectric cross-field control in a single phase rare earth titanate film. In bulk form, EuTiO3 is antiferromagnetic. However, both anti and ferromagnetic interactions coexist between different nearest neighbor europium ions. In thin epitaxial films, strain can be used to alter the relative strength of the magnetic exchange constants. Here, we not only show that moderate biaxial compression precipitates local magnetic competition, but also demonstrate that the application of an electric field at this strain state, switches the magnetic ground state. Using first principles density functional theory, we resolve the underlying microscopic mechanism resulting in the EuTiO3 G-type magnetic structure and illustrate how it is responsible for the 'giant' cross-field magnetoelectric effect

Алгоритм проведення первинної статистичної обробки масивів експериментальних даних

Purpose. Construction of an algorithm for preliminary (primary) estimation of arrays of experimental data for further obtaining a mathematical model of the process under study. Methodology. The use of the main regularities of the theory of processing arrays of experimental values in the initial analysis of data. Originality. An algorithm for performing a primary statistical analysis of the arrays of experimental data is given. Practical value. Development of methods for revealing statistically unreliable values in arrays of experimental data for the purpose of their subsequent detailed analysis and construction of a mathematical model of the studied processes.Цель статьи. Построение алгоритма предварительной (первичной) оценки массивов экспериментальных данных для дальнейшего получения математической модели исследуемого процесса. Методика. Использование основных закономерностей теории обработки массивов экспериментальных значений при первичном анализе данных. Научная новизна. Приведен алгоритм проведения первичного статистического анализа массивов экспериментальных данных. Практическая значимость. Разработка методов выявления статистически не достоверных значений в массивах экспериментальных данных с целью последующего их детального анализа и построения математической модели исследуемых процессов.Мета статті. Побудова алгоритму попередньої (первинної) оцінки масивів експериментальних даних для подальшого математичного моделювання процессу, що досліджується. Методика. Використання основних закономірностей теорії обробки масивів експериментальних значень для попереднього аналізу даних. Наукова новизна. Наведено алгоритм проведення первинного статистичного аналізу масивів експериментальних даних. Практична значимість. Розробка методів виявлення статистично не достовірних значень у масивах експериментальних даних із метою наступного детального аналізу та побудови математичних моделей процесів, що досліджуються