Flux growth at ambient pressure of millimeter-sized single crystals of LaFeAsO, LaFeAsO1−xFx, and LaFe1−xCoxAsO

Neutron and synchrotron resonant x-ray magnetic scattering (RXMS) complemented by heat capacity and resistivity measurements reveal the evolution of the magnetic structures of Fe and Ce sublattices in a CeFeAsO single crystal. The RXMS of magnetic reflections at the Ce L-II edge shows a magnetic transition that is specific to the Ce antiferromagnetic long-range ordering at T-Ce approximate to 4 K with short-range Ce ordering above T-Ce, whereas neutron diffraction measurements of a few magnetic reflections indicate a transition at T* approximate to 12 K with an unusual order parameter. Detailed order-parameter measurements on several magnetic reflections by neutrons show a weak anomaly at 4 K that we associate with the Ce ordering. The successive transitions at T-Ce and T* can also be clearly identified by two anomalies in heat capacity and resistivity measurements. The higher transition temperature at T* approximate to 12 K is mainly ascribed to Fe spin reorientation transition, below which Fe spins rotate uniformly and gradually in the ab plane. The Fe spin reorientation transition and short-range Ce ordering above T-Ce reflect the strong FeCe couplings prior to long-range ordering of the Ce. The evolution of the intricate magnetic structures in CeFeAsO going through T* and T-Ce is proposed. Neutron and synchrotron resonant x-ray magnetic scattering (RXMS) complemented by heat capacity and resistivity measurements reveal the evolution of the magnetic structures of Fe and Ce sublattices in a CeFeAsO single crystal. The RXMS of magnetic reflections at the Ce L II edge shows a magnetic transition that is specific to the Ce antiferromagnetic long-range ordering at T Ce ≈ 4 K with short-range Ce ordering above T Ce , whereas neutron diffraction measurements of a few magnetic reflections indicate a transition at T * ≈ 12 K with an unusual order parameter. Detailed order-parameter measurements on several magnetic reflections by neutrons show a weak anomaly at 4 K that we associate with the Ce ordering. The successive transitions at T Ce and T * can also be clearly identified by two anomalies in heat capacity and resistivity measurements. The higher transition temperature at T * ≈ 12 K is mainly ascribed to Fe spin reorientation transition, below which Fe spins rotate uniformly and gradually in the ab plane. The Fe spin reorientation transition and short-range Ce ordering above T Ce reflect the strong Fe-Ce couplings prior to long-range ordering of the Ce. The evolution of the intricate magnetic structures in CeFeAsO going through T * and T Ce is proposed. Disciplines Condensed Matter Physics | Materials Science and Engineering | Metallurgy Comments

Section: Methodsmentioning

confidence: 99%

Magnetic structures and interplay between rare-earth Ce and Fe magnetism in single-crystal CeFeAsO

Zhang

Kim

et al. 2013

“…14 Crystal quality was characterized by Laue backscattering, x-ray powder-diffraction, heat-capacity, magnetization, and resistivity measurements. A large LaFeAsO single crystal ͑ϳ20 mg͒ was selected for this study.…”

Section: Methodsmentioning

confidence: 99%

“…The refined structural parameters listed in Table I are in agreement with previous reports. 7,14 Figure 3 shows the temperature evolution of the structural and magnetic transitions in the single crystal measured by neutron diffraction on HB-1A. For the structural transition, the ͑400͒ O / ͑040͒ O and ͑006͒ O ͑Cmma͒ reflections were monitored.…”

Section: A Structural and Magnetic Transitionsmentioning

confidence: 99%

“…Such crystals are now available with the recent successful growth of relatively large 1111 single crystals at ambient pressure. 14 Here we report elastic neutron-scattering and synchrotron x-ray powder-diffraction studies on the bulk and pulverized LaFeAsO single crystals, respectively, focusing on the de- tails of the structural and magnetic transitions as well as the coupling between them, and the measurement of the average ordered magnetic moment size and its spatial distribution by extracting the magnetic form factor of iron in this compound.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Phase transitions and iron-ordered moment form factor in LaFeAsO

Yan

Zarestky

et al. 2010

Self Cite

Elastic neutron-scattering studies of single-crystal LaFeAsO reveal that upon cooling, an onset of the tetragonal (T)-to-orthorhombic (O) structural transition occurs at T S ≈156 K, and it exhibits a sharp transition at T P ≈148 K. We argue that in the temperature range T S to T P , T and O structures may dynamically coexist possibly due to nematic spin correlations recently proposed for the iron pnictides, and we attribute T P to the formation of long-range O domains from the finite local precursors. The antiferromagnetic structure emerges at T N ≈140 K, with the iron moment direction along the O a axis. We extract the iron magnetic form factor and use the tabulated ⟨j 0 ⟩ of Fe, Fe2+, and Fe3+ to obtain a magnetic moment size of ∼0.8 μ B at 9.5 K. Keywords Physics and Astronomy, Materials Science and Engineering Disciplines Condensed Matter Physics | Materials Science and Engineering CommentsThis article is from Physical Review B 82 (2010) Elastic neutron-scattering studies of single-crystal LaFeAsO reveal that upon cooling, an onset of the tetragonal ͑T͒-to-orthorhombic ͑O͒ structural transition occurs at T S Ϸ 156 K, and it exhibits a sharp transition at T P Ϸ 148 K. We argue that in the temperature range T S to T P , T and O structures may dynamically coexist possibly due to nematic spin correlations recently proposed for the iron pnictides, and we attribute T P to the formation of long-range O domains from the finite local precursors. The antiferromagnetic structure emerges at T N Ϸ 140 K, with the iron moment direction along the O a axis. We extract the iron magnetic form factor and use the tabulated ͗j 0 ͘ of Fe, Fe 2+ , and Fe 3+ to obtain a magnetic moment size of ϳ0.8 B at 9.5 K.

“…19 Crystal quality was characterized by Laue backscattering, x-ray powderdiffraction, heat capacity, magnetization, and resistivity measurements. A large as-grown platelike CeFeAsO single crystal (∼5 mg) with the crystallographic c axis perpendicular to its surface was selected.…”

mentioning

confidence: 99%

Anisotropic magnetoelastic coupling in single-crystalline CeFeAsO as seen via high-resolution x-ray diffraction

Yan

Kim

et al. 2011

Self Cite

Single-crystal synchrotron X-ray diffraction studies of CeFeAsO reveal strong anisotropy in the charge correlation lengths along or perpendicular to the in-plane antiferromagnetic (AFM) wavevector at low temperatures, indicating an anisotropic two-dimensional magnetoelastic coupling. The high-resolution setup allows to distinctly monitor each of the twin domains by virtue of a finite misfit angle between them that follows the order parameter. In addition, we find that the in-plane correlations, above the orthorhombic (O)-to-tetragonal (T) transition, are shorter than those in each of the domains in the AFM phase, indicating a distribution of the in-plane lattice constants. This strongly suggests that the phase above the structural O-to-T transition is virtually T with strong O-T fluctuations that are probably induced by spin fluctuations.