Temperature-dependent Neutron Diffraction Research Articles

First order paramagnetic–ferromagnetic phase transition in Tb 3+ doped La 0.5Ca 0.5MnO 3 manganite

Effect of A-site disorder in half-doped La 0.5Ca 0.5MnO 3 created by the substitution of Tb at La site is studied through temperature dependent neutron diffraction, resistivity, and magnetization on La 0.375Tb 0.125Ca 0.5MnO 3 (LTC) to identify the evolution of phases as a function of temperature and magnetic field. Contrary to the parent system, the paramagnetic (PM) to ferromagnetic (FM) transition is found to be of first order but becomes observable only in fields above 1 T. Absence of this transition in zero and low fields along with the observation of a very intriguing and irreversible M– H curve at low temperature raises the question about the ground state of the system. It is identified from the specially designed measurement protocol that the ground state of the system becomes FM, contrary to the parent LCMO. However, this remains masked because of the hindrance to the transformation kinetics of the PM–FM first order transition in low fields. Significantly, though the thermal hysteresis of the first-order transition decreases with the measurement field, collapse of such a behavior to a critical point is not observed in LTC, unlike earlier observations in some other manganites.

Phase stability and structural temperature dependence in sodium niobate: A high-resolution powder neutron diffraction study

We report investigation of structural phase transitions in technologically important material sodium niobate as a function of temperature on heating over 300-1075 K. Our high resolution powder neutron diffraction data show variety of structural phase transitions ranging from non-polar antiferrodistortive to ferroelectric and antiferroelectric in nature. Discontinuous jump in lattice parameters is found only at 633 K that indicates that the transition of orthorhombic antiferroelectric P (space group Pbcm) to R (space group Pbnm) phase is first order in nature, while other successive phase transitions are of second order. New superlattice reflections appear at 680 K (R phase) and 770 K (S phase) that could be indexed using an intermediate long-period modulated orthorhombic structure whose lattice parameter along <001> direction is 3 and 6 times that of the CaTiO3-like Pbnm structure respectively. The correlation of superlattice reflections with the phonon instability is discussed. The critical exponent ({\beta}) for the second order tetragonal to cubic phase transition at 950 K, corresponds to a value {\beta}$\approx 1/3$, as obtained from the temperature variation of order parameters (tilt angle and intensity of superlattice reflections). It is argued that this exponent is due to a second order phase transition close to a tricritical point. Based on our detailed temperature dependent neutron diffraction studies, the phase diagram of sodium niobate is presented that resolves existing ambiguities in the literature.

Magnetic structure of the Mn 5Si 3-type Er 5Si 3 compound

Neutron diffraction study has been performed on the Er 5Si 3 compound (hexagonal Mn 5Si 3-type, hP16, P6 3/mcm ) to understand its magnetic structure. The temperature dependent neutron diffraction results prove that this compound shows a complex antiferromagnetic ordering with sine modulated magnetic moments collinear to the c axis, presenting three subsequent changes in magnetization at ∼29 K, 13 K and 10 K on cooling. The high-temperature magnetic component of Er 5Si 3 ( C 3v magnetic point group, P31m magnetic space group, K 1 = [0, 0, ±0.277(2)]) exists from 29 K to 10 K, whereas low-temperature magnetic component (symmetry C 1v magnetic point group, Pm magnetic space group, K 2 = [0, ±1/4, 0]) exists from 13 K down to 1.5 K. The low-temperature and high-temperature magnetic components coexist between 13 K and 10 K.

Temperature-dependent neutron diffraction studies on iron pnictide single crystals

Temperature-dependent neutron diffraction studies on iron pnictide single crystals

ChemInform Abstract: Structure and Magnetic Ordering of Holmium Carbide Fluoride, Ho2CF2.

Abstract The preparation of a new rare earth carbide fluoride, Ho 2 CF 2 , is described. Ho 2 CF 2 is trigonal, space group P 3 m1 , Z =1, with a=3.6567(2) A and c=6.3171(5) A at room temperature. On cooling below the Neel temperature of 3.7 K, Ho 2 CF 2 transforms to an antiferromagnet with magnetic space group P a 1 ′ . The phase transition from the paramagnetic to antiferromagnetic state is accompanied by a distortion of the lattice to P 1 due to magnetoelastic effects. The nuclear and magnetic structures have been fully determined from high resolution powder neutron diffraction measurements at 1.5 and 50 K. Evidence for critical scattering above T N is shown from specific heat, magnetic susceptibility and temperature-dependent neutron diffraction studies. Electrical conductivity measurements show that Ho 2 CF 2 is an insulator. The relationship between the low dimensionality of the structure and the magnetic and physical properties of Ho 2 CF 2 is discussed.

Magnetocaloric effect and critical behavior near the paramagnetic to ferrimagnetic phase transition temperature inTbCo2−xFex

Magnetocaloric effect (MCE) in TbCo2-xFex has been studied by dc magnetization measurements.On substituting Fe in TbCo2, not only the magnetic transition temperature is tuned to room temperature, but also the operating temperature range for MCE is increased from 50 K for TbCo2 to 95 K for TbCo1.9Fe0.1. The maximum magnetic entropy change (-{\Delta}SM) for TbCo1.9Fe0.1 is found to be 3.7 J kg-1 K-1 for a 5 T field change, making it a promising candidate for magnetic refrigeration near room temperature. The temperature dependent neutron diffraction study shows a structural phase transition (from cubic to rhombohedral phase with lowering of temperature) which is associated with the magnetic phase transition and these transitions broaden on Fe substitution. To investigate the nature of the paramagnetic to ferrimagnetic phase transition, we performed a critical exponent study. From the derived values of critical exponents, we conclude that TbCo2 belongs to the 3D Heisenberg class with short-range interaction, while on Fe substitution it tends towards mean-field with long-range interaction. The derived values of critical exponents represent the phenomenological universal curve for the field dependence of {\Delta}SM, indicating that TbCo2 and TbCo1.9Fe0.1 belong to two different universality classes.

Magnetic field dependent neutron powder diffraction studies of Ru0.9Sr2YCu2.1O7.9

Temperature and magnetic field dependent neutron diffraction has been used to study the magnetic order in Ru0.9Sr2YCu2.1O7.9. The appearance of (1/2, 1/2, 1/2), (1/2, 1/2, 3/2), and (1/2, 1/2, 5/2) peaks below TM=140 K manifests the antiferromagnetic order. Neutron diffraction patterns measured in applied magnetic fields from 0 to 6 T show the destruction of the antiferromagnetic order with increasing field. There is no evidence of spontaneous or field-induced long range ferromagnetic order. This latter result contradicts the vast majority of other experimental observations for this system.

Magnetic phase coexistence in Tb +3- and Sr +2-doped La 0.7Ca 0.3MnO 3 manganite:A temperature-dependent neutron diffraction study

We report the results of the temperature-dependent neutron diffraction measurements on the nearly half-doped (La 0.325Tb 0.125)(Ca 0.3Sr 0.25)MnO 3 manganite sample. The simultaneous doping of magnetic Tb 3+ and divalent Sr 2+ in the La 0.7Ca 0.3MnO 3 system results into a large A-site size disorder. Rietveld refinement of neutron diffraction data reveal that the single phase sample crystallizes in a distorted orthorhombic structure. Increased 〈 r A〉 value affects the transport behavior that results into an insulating-like behavior of the sample. Under application of 1 T field sample exhibit insulating-like behavior while insulator–metal transition ( T IM) is exhibited under 5 and 8 T fields. Variable range hoping (VRH) mechanism of charge carriers is exhibited in the insulating region. Field cooled and zero field cooled magnetization measurement shows the Curie temperature ( T C)~47 K. The refinement of the ND data collected at various temperatures below 300 K shows that there is no structural phase transition in the compound. Around 100 K, a magnetic peak appears at lower angle that can be ascribed to the presence of the A-type antiferromagnetic (AFM) phase. Two more peaks are observed around 50 K at lower angles that can be fitted in CE-type antiferromagnetic phase. Splitting of the peaks at lower temperatures is the signature of orbital ordering in the presently studied nearly half-doped manganite system. Results of the detailed structural analysis of the temperature-dependent ND measurements on (LaTb) 0.45(CaSr) 0.55MnO 3 sample has been discussed in the light of coexisting A-type and CE-type antiferromagnetic phases present in the sample at low temperature.

Temperature-dependent neutron diffraction study of phase separation at morphotropic phase boundary in (1−x)BiScO3–xPbTiO3

We report the results of temperature-dependent neutron powder diffraction experiments on (1−x)BiScO3–xPbTiO3 (x=0.62, 0.64, and 0.66) within the morphotropic phase boundary. In all samples the monoclinic phase is found to coexist with the tetragonal phase below the ferroelectric transition temperature. The details of structural information demonstrate a delicate balance between the coexisting two phases for x=0.64. Such delicate balance is suggested to be sensitive to an external electric field, thus responsible for the enhanced electromechanical properties observed for x=0.64. Our result reveals that phase separation and the delicate balance between two phases are crucial to understand the unique properties at the morphotropic phase boundary in (1−x)BiScO3–xPbTiO3 ferroelectric systems.

Local and average structures of the spin-glass pyrochloreY2Mo2O7from neutron diffraction and neutron pair distribution function analysis

The observation of canonical spin-glass behavior in the pyrochlore oxide ${\text{Y}}_{2}{\text{Mo}}_{2}{\text{O}}_{7}$ has been a subject of considerable interest as the original structural studies were interpreted in terms of a well-ordered crystallographic model. It is widely held that the stabilization of the spin-glass state requires some level of positional disorder along with frustration. Recent reports from local probe measurements, extended x-ray-absorption fine structure (EXAFS) and $^{89}\text{Y}$ NMR, have been interpreted in terms of disorder involving the Mo-Mo distances (EXAFS) and multiple Y sites (NMR). This work reports results from temperature-dependent (15--300 K) neutron diffraction (ND) and neutron pair distribution function studies which can provide from the same data set information on both the average and local structures. The principal findings are that: (1) there is no crystallographic phase transition over the temperature region studied within the resolution of the ND data; (2) the diffraction data are well fitted using a fully ordered model but with large and anisotropic displacement parameters for three of the four atomic sites; (3) the pairwise real-space correlation function $G(r)$ shows clear evidence that the principal source of disorder is associated with the Y-O1 atom pairs rather than the Mo-Mo pairs, in disagreement with the interpretation of the EXAFS results; (4) fits to the $G(r)$ improve significantly when anisotropic displacements for all sites are included; (5) inclusion of a split-site position parameter for O1 improves, slightly, both the $G(r)$ fits and the Rietveld fits to the ND data; and (6) for all models the fits become worse as the temperature decreases and as the fitting range decreases. These results are qualitatively consistent with the $^{89}\text{Y}$ NMR observations and perhaps recent muon-spin-relaxation studies. The issue of static versus dynamic disorder is not resolved, definitively. An estimate of the distribution of exchange constants due to the disorder is made using spin-dimer analysis and compared with the Saunders-Chalker model for the generation of spin-glass behavior from ``weak'' disorder on geometrically frustrated lattices.

Long-Range Antiferromagnetic Ordering in the Novel Magnetically Frustrated Rock Salt Oxide System: Li3Mg2RuO6

The new ruthenate, Li3Mg2RuO6, was synthesized in polycrystalline form by a solid-state method. The crystal structure of Li3Mg2RuO6 was refined from powder neutron diffraction data in the orthorhombic Fddd space group in an ordered NaCl structure type with a = 5.8759 (2) Å, b = 8.4206 (1) Å, and c = 17.6455 (5) Å. The Ru5+ (S = 3/2) sublattice shows a unique topology, which consists of chains of edge-sharing triangles interconnected by corner sharing and thus there exists the potential for geometric magnetic frustration. This is the first time that magnetic behavior of a material with such sublattice has been investigated. The isostructural, nonmagnetic Li3Mg2NbO6 was prepared as the lattice match for the heat capacity analysis. The temperature-dependent magnetic susceptibility, heat capacity, and neutron diffraction data reveal that the system undergoes a long-range AFM ordering below 17 K but also provide evidence for short-range spin correlations well above TN. The magnetic frustration index, f ≈ 109/17 = 6.4 suggests that the system is geometrically frustrated. Spin dimer analysis of the magnetic exchange interactions supports this characterization. Comparisons are made with other materials containing the Ru5+ ion on geometrically frustrated lattices.

Magnetic properties and magnetic structure of the Mn5Si3-type Tb5Si3 compound

Abstract Neutron diffraction and magnetization measurements have been performed on the Tb5Si3 compound (hexagonal Mn5Si3-type, hP16, P63/mcm) to understand its magnetic structure and magnetic properties. The temperature-dependent neutron diffraction results prove that this intermetallic phase shows a complex flat spiral magnetic ordering, presenting three subsequent changes in magnetization at T m 1 Neu ∼ 100 K , T m 2 Neu = 62 ( 4 ) K and T m 3 Neu = 54 ( 4 ) K on cooling. However, the magnetization data depict two transitions at 72 K (TN1) and 55 K (TN2). The extended temperature range between T m 1 Neu and T m 2 Neu over which the neutron diffraction patterns slowly evolve might correspond to the high-temperature antiferromagnetic transition at TN1 and low-temperature antiferromagnetic transition at TN2 of the magnetic data. Between T m 1 Neu ∼ 100 K and T m 2 Neu = 62 ( 4 ) K Tb5Si3 shows a flat spiral antiferromagnetic ordering with a propagation vector K1 = [0,0, ±1/4]; then, between T m 2 Neu = 62 ( 4 ) K and T m 3 Neu = 54 ( 4 ) K the flat spiral type ordering is conserved, but by two coexisting propagation vectors K1 = [0,0, ±1/4] and K2 = [0,0, ±0.4644(3)]. The terbium magnetic moments arrange in the XY(ab) plane of the unit cell. Below T m 3 Neu = 54 ( 4 ) K the magnetic component with K1 = [0,0, ±1/4] vanishes and magnetic structure of Tb5Si3 is a flat spiral with K2 = [0,0, ±0.4644(3)], only. Low field magnetization measurements confirm the occurrence of complex, multiple magnetic transitions. The field dependence of the magnetization indicates a metamagnetic transition at a critical field of ∼3 T.

Magnetic structure, magnetic interactions and metamagnetism in terbium iron borateTbFe3(BO3)4: a neutron diffraction and magnetization study

Magnetization, susceptibility and neutron scattering measurements were performed on the terbium ironborate TbFe3(BO3)4. Structural and magnetic phase transitions were obtained as a function of externalmagnetic field and temperature. A metamagnetic transition of the terbium spins and aspin-flop transition of the iron sublattice are obtained at an external magnetic field35 kOe<Ht<60 kOe. The values ofthe effective exchange HE and the anisotropy HA fields are evaluated. Temperature dependent neutron diffraction studies reveal the magnetic structureof TbFe3(BO3)4 and the thermal evolution of the two magnetic sublattices. An antiferromagnetic couplingalong the helicoidal chains of Fe atoms sets in at 40 K with a propagation vector . The magnetic ordering of the Tb sublattice sets in at the same temperatureand leads to an anti-parallel alignment of the Fe and Tb moments within thea–b-planeswith μFe = 4.4 µB and μTb = 8.6 µB at 2 K.

Powder neutron diffraction evidence for enhanced inter plane magnetic coupling in La1.2Sr1.8Mn2−xRuxO7 layered manganites

Rotation of Mn spin moments along the c axis enhances interplane magnetic coupling, leading to a steep increase in the Curie temperature (TC) and metal to insulator transition (TMIT) in Ru substituted two dimensional layered manganites, La1.2Sr1.8Mn2−xRuxO7. The temperature dependent neutron diffraction data show the absence of (004) reflection, indicating that the Mn spin moments are not aligned in the a-b plane, and rather the increase in intensity of (110) reflection at 12K shows that the MnO2 layers are stacked ferromagnetically along the c axis. The presence of Ru at the Mn site in pentavalent state assures the required hole carrier density for a sustained double-exchange interaction. The cumulative effect of rotation of Mn spin moments and the variable valence states of Ru lead to a pronounced increase in TC up to ∼50K, which is not observed hitherto in any of the B-site substituted manganites.

Magnetic structural characterization of Mg–Co–Cr ferrite by neutron diffraction

Temperature-dependent neutron diffraction studies were done on the spinel oxide system Mg x Co 1− x Cr x Fe 2− x O 4 ( x=0.0, 0.25, 0.50, 0.75 and 1.0). Neutron diffraction data recorded in the temperature range 10–810 K were analyzed in the Rietveld method. Ordered sublattice magnetic moments of the five compositions of the spinel series at various temperatures were deduced from the analysis. A decreasing ordered moment with increasing substitution ( x) was found indicating a gradual weakening of ferrimagnetic order. Huge diffuse signals around the 1 1 1 Bragg diffraction peak were found in the neutron patterns of the composition x=1.0 below the Curie temperature manifesting a build-up of short-range magnetic spin clusters. The observed features suggest a canted ferrimagnetic structure in the composition range x⩽0.75 and a semi-spin glass-like transition at x=1.0.

The crystal and magnetic structures of the organic–inorganic layer compound phenylphosphonato-Mn(II)-hydrate: A synchrotron X-ray and neutron powder diffraction study

The crystal and magnetic structures of the organic–inorganic layer compound phenylphosphonato-Mn(II)-hydrate, C 6D 5PO 3Mn⋅D 2O, have been studied by powder diffraction using synchrotron X-rays and neutrons. The crystal structure is resolved by both techniques including orientational disorder of the phenyl-groups. Temperature-dependent neutron diffraction peaks below 12 K are identified as magnetic in origin; their indices show that the magnetic structure is closely similar to that of KMnPO 4⋅H 2O.

Magnetic order in the organic–inorganic layer compound (CD3PO3)Mn·D2O: a neutron and synchrotron X-ray powder diffraction study

Both long- and short-range magnetic order in the organic–inorganic layer compound (CD3PO3)Mn·D2O has been studied by temperature-dependent powder neutron diffraction. Above 15 K the magnetic intensity is dominated by diffuse scattering due to two-dimensional short-range order while at lower temperatures Bragg diffraction indicates three-dimensional order. The long-range ordered magnetic structure is similar to that of AMnPO4·D2O (A = K, ND4). The crystal structure of (CD3PO3)Mn·D2O has been refined from neutron and synchrotron X-ray powder diffraction, including location of all D atoms.

Magnetic and neutron diffraction studies of long-range ferromagnetic order in monolayered manganites

The structural, magnetic, and electrical properties of single crystals of Ru-doped monolayered manganites La 0 . 5 Sr 1 . 5 Mn 1 - x Ru x O 4 (0≤x≤0.5) were investigated by neutron-diffraction, magnetization, and transport measurements. With increasing Ru content, the magnetic ground state changed from the parent antiferromagnetic (AFM) to the spin-glass to the ferromagnetic (FM) phase. The temperature-dependent neutron-diffraction measurements at x=0.35 clearly revealed long-range FM order in the monolayered manganite, which was confirmed by bulk magnetometry. The uniaxial magnetic anisotropy, in which the Ru spins are aligned along the c axis, was also observed in the compounds. This unique magnetic behavior might be ascribed to the magnetic anisotropy of the Ru ions stabilized under the structural distortion, as well as the FM ordering of Mn spins induced by AFM coupling among Mn/Ru pairs. The magnetoresistance of the Ru-doped system, which exhibits conduction confinement within a layer, diminishes with increasing Ru doping because of an increase in the proportion of FM domains at the expense of the magnetic glassy state.

Studies of the magnetic behavior of the spinel system GaxCoCrFe1−xO4 by neutron diffraction

Temperature dependent neutron diffraction studies have been done on the spinel series GaxCoCrFe1−xO4 with x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0. Magnetic properties of the system have been determined from the analysis of neutron data recorded at a number of temperatures. The sublattice and net magnetizations and the paramagnetic transition temperatures of all the members of the series have been found out. A decreasing ferrimagnetic order with increasing x is apparent from the progressive loss of magnetization and transition temperature. Evidence of magnetic spin clusters has been revealed from the reduced sublattice moments and diffuse signal appearing below the (1 1 1) Bragg peak at low temperature neutron patterns. A weak magnetic ordering has also been revealed from the magnetization measurements on the sample x=1.0. The system has been found to exhibit a complex magnetic phenomenon in which short-range magnetic spin clusters are superimposed on the ferrimagnetic long-range order together with a little extension of the short-range ordering of spin clusters at very low temperatures giving rise to a weak (2 0 0) superlattice reflection.

Synthesis, Magnetic and Electronic Properties of Single Crystals of EuMn2P2

Large single crystals of EuMn2P2 were grown from a tin flux whose melt composition and reaction temperature profile were optimized to avoid impurity phases. The crystal structure of EuMn2P2 is of the CaAl2Si2 structure type. The structure was determined by single-crystal X-ray crystallography, with the unit cell in the trigonal lattice, a=4.1294(3) Å and c=6.9936(8) Å, at T=90 K (Z=1, R1=0.0239, wR2=0.0632) and belongs to the P3m1 (#164) space group. Temperature-dependent magnetic susceptibility, resistivity, and neutron diffraction measurements on single crystals indicate that EuMn2P2 is an antiferromagnetic insulator with a Neél temperature of 16.5±0.25 K. The Eu spins order in a simple magnetic structure where the spins in the a–b plane are aligned ferromagnetically; these ferromagnetic planes are stacked antiferromagnetically along the c-axis.