Identification of microscopic spin-polarization coupling in the ferroelectric phase of a magnetoelectric multiferroic CuFe1-xAlxO2

We have performed synchrotron radiation X-ray and neutron diffraction measurements on magnetoelectric multiferroic CuFe1-xAlxO2 (x=0.0155), which has a proper helical magnetic structure with incommensurate propagation wave vector in the ferroelectric phase. The present measurements revealed that the ferroelectric phase is accompanied by lattice modulation with a wave number 2q, where q is the magnetic modulation wave number. We have calculated the Fourier spectrum of the spatial modulations in the local electric polarization using a microscopic model proposed by Arima [T. Arima, J. Phys. Soc. Jpn. 76, 073702 (2007)]. Comparing the experimental results with the calculation results, we found that the origin of the 2q-lattice modulation is not conventional magnetostriction but the variation in the metal-ligand hybridization between the magnetic Fe^3+ ions and ligand O^2- ions. Combining the present results with the results of a previous polarized neutron diffraction study [Nakajima et al., Phys. Rev. B 77 052401 (2008)], we conclude that the microscopic origin of the ferroelectricity in CuFe1-xAlxO2 is the variation in the metal-ligand hybridization with spin-orbit coupling.Comment: 11 pages, 9 figures, to be published in Phys. Rev.

Magnetic Structure and Interactions in the Quasi-1D Antiferromagnet CaV2_2O4_4

CaV$_2$O$_4$ is a spin-1 antiferromagnet, where the magnetic vanadium ions are arranged on quasi-one-dimensional (1D) zig-zag chains with potentially frustrated antiferromagnetic exchange interactions. High temperature susceptibility and single-crystal neutron diffraction measurements are used to deduce the non-collinear magnetic structure, dominant exchange interactions and orbital configurations. The results suggest that at high temperatures CaV$_2$O$_4$ behaves as a Haldane chain, but at low temperatures, orbital ordering lifts the frustration and it becomes a spin-1 ladder.Comment: 5 pages, 4 figure

Solitonic lattice and Yukawa forces in the rare earth orthoferrite TbFeO3

The control of domains in ferroic devices lies at the heart of their potential for technological applications. Multiferroic materials offer another level of complexity as domains can be either or both of a ferroelectric and magnetic nature. Here we report the discovery of a novel magnetic state in the orthoferrite TbFeO3 using neutron diffraction under an applied magnetic field. This state has a very long incommensurate period ranging from 340 Angstrom at 3K to 2700 Angstrom at the lowest temperatures and exhibits an anomalously large number of higher-order harmonics, allowing us to identify it with the periodic array of sharp domain walls of Tb spins separated by many lattice constants. The Tb domain walls interact by exchanging spin waves propagating through the Fe magnetic sublattice. The resulting Yukawa-like force, familiar from particle physics, has a finite range that determines the period of the incommensurate state.Comment: 11 pages 14 figure

Gradual localization of 5f states in orthorhombic UTX ferromagnets - polarized neutron diffraction study of Ru substituted UCoGe

We report on a microscopic study of the evolution of ferromagnetism in the Ru substituted ferromagnetic superconductor (FM SC) UCoGe crystallizing in the orthorhombic TiNiSi-type structure. For that purpose, two single crystals with composition UCo0.97Ru0.03Ge and UCo0.88Ru0.12Ge have been prepared and characterized by magnetization, AC susceptibility, specific heat and electrical resistivity measurements. Both compounds have been found to order ferromagnetically below TC = 6.5 K and 7.5 K, respectively, which is considerably higher than the TC = 3 K of the parent compound UCoGe. The higher values of TC are accompanied by enhanced values of the spontaneous moment mspont. = 0.11 mB/f.u. and mspont. = 0.21 mB/f.u., respectively in comparison to the tiny spontaneous moment of UCoGe (about 0.07mB/f.u.). No sign of superconductivity was detected in either compound. The magnetic moments of the samples were investigated on the microscopic scale using polarized neutron diffraction (PND) and for UCo0.88Ru0.12Ge also by soft X-ray magnetic circular dichroism (XMCD). The analysis of the PND results indicates that the observed enhancement of ferromagnetism is mainly due to the growth of the orbital part of the uranium 5f moment mL(U), reflecting a gradual localization of the 5f electrons with Ru substitution. In addition, the parallel orientation of the U and Co moments has been established in both substituted compounds. The results are discussed and compared with related isostructural ferromagnetic UTX compounds (T - transition metals, X - Si, Ge) in the context of a varying degree of the 5f-ligand hybridization

Magneticke struktury a souvisejici fyzikalni vlastnosti systemu s f elektrony.

Available from STL, Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi

E4: The 2-Axis Diffractometer at BER II

The double-axis diffractometer E4 is operated by the Helmholtz-Zentrum Berlin. It is suited for magnetic structure determinations and parametric studies on single crystals in a wide range of external conditions. Pyrolytic graphite and germanium focusing monochromators offer two fixed neutron incident wavelengths of about 1.0*106 ncm-2s-1

Elastic Neutron Diffraction on Magnetic Materials

The neutron as an elementary particle has been discovered in 1932 by Chadwick and soon it was recognized as being useful for studies of magnetic materials Bloch, 1936 . Since the first successful experiments in the mid of last century by Shull and Brockhouse, it has been used for studying various materials both were awarded in 1994 with the Nobel Prize for Physics, for the development of different neutron techniques . Today, neutron scattering and diffraction are among the most widely used microscopic tools in condensed matter research, especially in the field of magnetism, phase transitions, and elementary collective excitations. It was the technique of choice to prove the existence of an antiferromagnetic state predicted by Ne el, another Nobel Prize laureate 1970 . An experiment on MnO has disclosed additional Bragg reflections at temperatures below the magnetic phase transition proving the appearance of a new periodicity in this material Shull and Smart, 1949 . Since then, neutron sciences have contributed enormously to the knowledge of human beings in many different fields and continue to do so till present Brammer, 2003; Bru ck, 2005; Catalan and Scott, 2009; Tokura, 2006; Zaccai, 2000 . A vast variety of different techniques have been developed and it is simply impossible to mention them all at this place in detail. For more detailed information, we advise the reader to consult several very excellent books Bacon, 1975; Furrer et al., 2008; Izyumov and Ozerov, 1970; Marshal and Lovesey, 1971; Squires, 1978 . In this chapter we give merely a dense overview of the elastic neutron diffraction technique as tool for studying magnetic materials, along with several representative examples documenting the main notions of this technique. The chapter is meant to help the reader to understand the variety of advantages and also limitations of the method. By no means is it supposed to duplicate many useful textbooks and texts already existin

Combination of methods of thermal and radiation treatment of sediments associated with PCBs : the Delor type

An efficient method of burning polychlorinated biphenyls (PCBs) is often used to remove the environmental burden of PCBs. However, combustion produces toxic dioxins and furans (PCDD/F), so residents are increasingly rejecting this method. The heat treatment (HT) method does not burn PCBs but evaporates it from sediments. Even in this process, PCDD/Fs are formed to a lesser extent, which are destroyed by radiation processing (RP) following the HT. At the same time, the RP method degrades PCB congeners down to biphenyls, which decompose easily in the environment. A block assembly of a complex synergistic combination of equipment for methods of thermal (HT) and radiation (RP) destruction of PCBs in sediments is proposed. The efficacy of this complex was preliminarily determined at a level of 70-fold reduction in PCB concentration in sediments. To achieve a higher reduction factor in the concentration of PCBs, possible procedures for optimizing the settings of individual devices of this complex are presented

OPTIMEX: Měření detonační rychlosti pasivním vláknovým systémem

Detonation velocity (VOD) is one of the most important parameters describing the detonation process of a particular explosive. This article summarizes some peculiarities that we have come across when building and testing our new passive optical VOD meter - OPTIMEX. The advantages of using multiple probes with independent signal recording is discussed. The practical issues related to an explosive's translucency are solved. Finally, a new method for detonation velocity data evaluation is proposed and demonstrated.Detonační rychlost je jedním z nejdůležitějších parametrů popisujících proces detonace konkrétní výbušiny. Tento článek shrnuje nekteré poznatky, ke kterým jsme došli v průběhu vývoje našeho nového pasivního přístroje, nazvaného OPTIMEX, pro měření detonační rychlosti. Jsou rozebrány výhody využití více oddělených měřících kanálů. Je popsáno vyřešení problému s transparentností výbušin. V závěru je navržena nová metoda vyhodnocení naměřených dat

Tuning the orbital-lattice fluctuations in the mixed spin-dimer system Ba3−xSrxCr2O8Ba_{3−x}Sr_xCr_2O_8

Abstract: In A3Cr2O8, where A = Sr or Ba, the Cr5+ ions surrounded by oxygen ions in a tetrahedral coordination are Jahn-Teller active. The Jahn-Teller distortion leads to a structural transition and a related emergence of three twinned monoclinic domains below the structural phase transition. This transition is highly dynamic over an extended temperature range for A = Sr. We have investigated mixed compounds Ba3−xSrxCr2O8 with x=2.9 and x=2.8 by means of X-ray and neutron diffraction, Raman scattering and calorimetry. Based on the obtained evolution of the phonon frequencies, we find a distinct suppression of the orbital-lattice fluctuation regime with increasing Ba content. This stands in contrast to the linear behaviour exhibited by unit cell volumes, atomic positions and intradimer spin-spin exchange interaction