Neutron powder diffraction study of the magnetoelectric relaxor Pb(Fe 2/3 W 1/3 )O 3 (original) (raw)
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Materials Research Bulletin, 2008
The structural and magnetic properties of the complex metal oxides Pb(Mn 1/2 Nb 1/2 )O 3 (PMNO) and Pb(Mn 1/4 Fe 1/4 Nb 1/2 )O 3 (PMFNO), which belong to a class of disordered perovskites have been studied. The magnetic susceptibilities of PMNO showed hysteresis between field cooled and zero-field cooled conditions below the transition of 15 K, suggesting that the material has a spinglass feature. Neutron diffraction patterns of PMNO showed no evidence of a long-range magnetic ordering at 1.5 K, which is consistent with spin-glass behavior. Rietveld refinements of neutron powder diffraction data collected at different temperatures between 1.5 and 700 K have been carried out in order to extract structural information. The crystal structure of this compound is cubic (space group Pm3m) within the whole temperature interval. The Mn and Nb ions were found to be disordered over the perovskite B-sites. The main feature of this structure is the positional disorder at the Pb site, the importance of which in connection with the ferroic transitions is briefly discussed. The Pb cations show a positional disorder shifting from their high-symmetry positions along the [1 1 1] direction. The effect of Fe-doping on PMNO has been studied. The substitution of Fe at the Mn site in PMFNO results in a small changes of the magnetic properties without significant differences in the crystal structures. The factors governing the observed structural and magnetic properties of PMNO and PMFNO are discussed and compared with those of other quaternary Mn-containing perovskites. For the PbB 3+ 1/2 Nb 1/2 O 3 series with the isomorphous substitution B 3+ , graphs of average lattice parameters of the perovskite phase and the temperatures of ferroelectric and magnetic phase transitions as functions of the B 3+ cation radius were constructed and are discussed. Influence of A-cation sublattice on magnetic properties is also considered. # (S.A. Ivanov), Per.Nordblad@angstrom.uu.se (P. Nordblad), Roland.Tellgren@mkem.uu.se (R. Tellgren), Hakan.Rundlof@mkem.uu.se (H. Rundlof).
The European Physical Journal B, 2019
Ceramic samples of the multiferroic perovskite Pb(Fe1−xScx) 2/3 W 1/3 O3 with 0 ≤ x ≤ 0.4 have been synthesized using a conventional solid-state reaction method, and investigated experimentally and theoretically using first-principle calculations. Rietveld analyses of joint synchrotron X-ray and neutron diffraction patterns show the formation of a pure crystalline phase with cubic (F m3m) structure with partial ordering in the B-sites. The replacement of Fe by Sc leads to the increase of the cation order between the B and B sites. As the non-magnetic Sc 3+ ions replace the magnetic Fe 3+ cations, the antiferromagnetic state of PbFe 2/3 W 1/3 O3 is turned into a ferrimagnetic state reflecting the different magnitude of the magnetic moments on the B and B sites. The materials remain ferroelectric relaxors with increasing Sc content. Results from experiments on annealed and quenched samples show that the cooling rate after high temperature annealing controls the degree of cationic order in Pb(Fe1−xScx) 2/3 W 1/3 O3 and possibly also in the undoped PbFe 2/3 W 1/3 O3.
Journal of Alloys and Compounds, 2016
We report on the studies of room temperature (RT) crystal structure, electric and magnetic properties of (1-x) Pb(Fe 1/2 Nb 1/2)O 3-x Pb(Fe 2/3 W 1/3)O 3 (PFN 1-x-PFW x) (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) solid solutions through the measurements of X-ray diffraction, FTIR, scanning electron microscopy (SEM), Neutron diffraction, Raman, Magnetic, Mössbauer and ferroelectric measurements. FTIR spectra showed two main perovskite related transmission bands. The SEM analysis shows an average grain size of 2µm for all the solid solutions. Rietveld refinement was performed on RT X-ray diffraction (XRD) and neutron diffraction (ND), which reveals, the monoclinic phase for x = 0.0 with space group Cm and Cubic phase for x = 1.0 with space group Pm-3m. In other words, increasing x, the samples exhibit a gradual phase transition from monoclinic to cubic. In addition, the Raman spectroscopy corroborates the change in structural symmetry from monoclinic (Cm) to cubic (Pm-3m) on varying x. The coexistence of both monoclinic and cubic symmetries was observed between x = 0.2 to 0.8. Magnetic measurements shows that, the magnetic phase transition from paramagnetic to antiferromagnetic (AFM) was observed at or above RT for x = 0.6 and above. The magnetic structure was refined using the propagation vector k = (½, ½, ½) and structure was found to be G-type antiferromagnetic. Magnetic properties (M-H loops) shows, a weak ferromagnetic behaviour with antiferromagnetic ordering at RT. At RT, x = 0.0 to 0.6 the samples exhibits disordered paramagnetic property but weakly coupled with antiferromagnetic domains. But, x = 0.8 and 1.0 samples show antiferromagnetic and they are weakly coupled with paramagnetic domains. The temperature dependent magnetisation (M(T)) confirms, the augmentation of Néel temperature (T N) from 155 K to 350 K on increasing x. Mössbauer spectroscopy confirms superparamagnetic nature with the presence of Fe in 3+ state and on increasing x, the spectra changes from doublet to sextet. The ferroelectric (P-E) study confirms the existence of ferroelectric ordering with leaky
Neutron Rietveld refinement of the incommensurate phase of the ordered perovskite Pb 2 CoWO 6
Acta Crystallographica Section B Structural Science, 2000
The incommensurate structure of lead cobalt tungstate has been refined by the Rietveld method on neutron data collected at 250 K. The space group is planar monoclinic I2/m(\alpha0\gamma)0s [a = 7.9602 (4), b = 5.6779 (3), c = 5.6967 (3) Å, \beta = 90.047 (5)°, \bf q_{\rm inc} = 0.9000 (9)\bf a^* + 0.1735 (6)\bf c^*]. The use of powder diffraction techniques to investigate ferroelastic modulated phases is discussed and compared with a previous polydomain single-crystal structural analysis. The modulated displacements of light atoms have been determined, allowing an accurate description of the modulation of both the cations and the O-atom framework. The refinement suggests a displacive model for the phase transition, involving significant atomic shifts for Pb atoms and a quite complex mixing of tilt and deformation of the oxygen octahedra. The average character of this modulated structure is antiferroelectric.
Solid State Sciences, 2007
Fe-Si alloy with a large content of 15 wt. % Si has been obtained in nanocrystalline state by mechanical alloying. The influence of the milling duration and heat treatment on the formation of the alloy, its structure and magnetic properties was investigated. The Fe-Si alloy is obtained after 4 hours of mechanical alloying as shown by X-ray diffraction measurements. Annealing of the as-milled powders leads to the formation of the Fe 3 Si intermetallic compound with a DO3-type superstructure. The progressive formation of the Fe-Si alloy during mechanical alloying and annealing was investigated by 57 Fe Mössbauer spectrometry. Thermal stability of the Fe-15 wt. % Si powders was studied by differential scanning calorimetry (DSC). The alloy formation is also shown by the decrease of the saturation Structural, magnetic and Mössbauer spectroscopy characterisation of the Fe-15 wt. %Si nanocrystalline powder obtained by mechanical alloying and annealing
Magnetoelectric relaxor and reentrant behaviours in multiferroic Pb(Fe2/3W1/3)O3 crystal
Scientific reports, 2016
Significant quenched disorder in crystal structure can break ferroic (magnetic or electric) long-range order, resulting in the development of ferroic glassy states at low temperatures such as magnetic spin glasses, electric dipolar glasses, relaxor ferroelectrics, etc. These states have been widely studied due to novel physical phenomena they reveal. Much less known are the effects of quenched disorder in multiferroics, i.e. the materials where magnetic and electric correlations coexist. Here we report an unusual behaviour in complex perovskite Pb(Fe2/3W1/3)O3 (PFW) crystals: the coexistence of electric relaxor, magnetic relaxor and antiferromagnetic (AFM) states. The most striking finding is the transformation of the AFM phase into a new reentrant-type magnetic glassy phase below Tg ≅ 10 K. We show that the behaviour at this transformation contrasts the typical behaviour of canonical spin glasses and is similar to the behaviour of relaxor ferroelectrics. Magnetoelectric effect is a...
Journal of Magnetism and Magnetic Materials, 1978
Polycrystalline Y-type barium cobalt ferrite (Ba2Co2Fe12O22; Co2Y) was synthesized using by the conventional ceramic method. At temperatures below 260 K, the crystal structure of Co2Y was determined to be hexagonal with the space group R3m. It showed a soft ferrimagnetic behavior with Hc = 113 Oe at 297 K and the Néel temperature (TN) was determined to be 615 K. Most of the super-lattice peaks of Co2Y coming from the spin structure decreased with increasing temperature. However, the super-lattice peak at 21.8 • increased with increasing temperature at temperatures above 200 K. In addition, we observed a change in the slope of the zero-field cooled magnetization under a low field of 0.01 T at 215 K due to a magnetic structure transition from a helical to a ferrimagnetic spin structure.
Structural and Electric Evidence of Ferrielectric State in Pb 2 MnWO 6 Double Perovskite System
Inorganic Chemistry, 2014
In this paper we describe the new ferri-electric compound Pb 2 MnWO 6 (PMW), a double perovskite that can be considered as a novel structural prototype showing complex nuclear structure and interesting electric properties. According to single-crystal synchrotron data, PMW crystallizes in the noncentrosymmetric polar group Pmc2 1 , in which the two symmetry-independent lead atoms give rise to a ferrielectric arrangement. The accurate crystallographic characterization indicates the presence of a complex distortion of the perovskite lattice driven by the local instability induced by the 6s 2 lone pair of the lead atoms. These peculiar structural features are confirmed by the complete electrical characterization of the system. Dielectric and transport measurements indicate an insulating character of the sample, while pyroelectric measurements point out a ferrielectric state characterized by different contributions. The magnetic transition at 45 K is accompanied by a magnetostrictive effect indicating a probable spin− lattice coupling. The characterizations carried out on PMW, showing the evidence of a coexistence of antiferromagnetism and ferrielectricity at low temperature, could lead to the definition of a new class of multiferroic materials.
Physica B: Condensed Matter, 2019
Disordered magnetoelectric Pb(Fe 2/3 W 1/3)O 3 (PFW) was synthesized through columbite solid state reaction method in pure perovskite phase. Saturation magnetization of 0.013μ B /f. u. was observed at 5K, with a clear opening in the magnetic hysteresis loop around the origin. Temperature dependent magnetic susceptibility (χ) measurements revealed two different magnetic orderings, T N1 ~ 350 K and another cusp, T N2 below 20 K. The neutron diffraction studies were carried out at different temperatures to understand the existence of the controversial T N2. The variation in the magnetic peak intensity clearly show that while decreasing temperature from 300 K to 2K the intensity of the magnetic peak increases. This observation along with the observation of hysteresis loop at temperature below 20 K and the cusp in magnetic susceptibility data, confirms the existence of interaction between weak ferromagnetism and antiferromagnetism rather than spin-glassy nature or magnetic clusters.
Physical Review B, 2014
Pb(Fe0.5Nb0.5)O3 (PFN), one of the few relaxor multiferroic systems, has a G-type antiferromagnetic transition at TN=143K and a ferroelectric transition at TC=385K. By using high-resolution neutron-diffraction experiments and a total scattering technique, we paint a comprehensive picture of the long- and short-range structures of PFN: (i) a clear sign of short-range structural correlation above TC, (ii) no sign of the negative thermal expansion behavior reported in a previous study, and (iii) clearest evidence thus far of magnetoelectric coupling below TN. We conclude that at the heart of the unusual relaxor multiferroic behavior lies the disorder between Fe3+ and Nb5+ atoms. We argue that this disorder gives rise to short-range structural correlations arising from O disorder in addition to Pb displacement.