Temperature Dependent Neutron Diffraction Study Research Articles

Ni3InSb: Synthesis, Crystal Structure, Electronic Structure, and Magnetic Properties

The ternary phase with the composition Ni3InSb has been synthesized by high-temperature synthesis and structurally characterized by a combination of X-ray analysis, neutron diffraction analysis, and theoretical calculations. The structure of Ni3InSb crystallizes in the orthorhombic space group Pnma with lattice constants a = 7.111(3) Å, b = 5.193(3) Å, and c = 8.2113(2) Å. The crystal structure contains ∼20 atoms in its unit cell, which are distributed over four crystallographically independent positions (two Ni, one In, and one Sb). The crystal structure can be considered as a ternary substitutional variant of Ni3Sn2 (Pnma, no. 62), where a trivalent In and a pentavalent Sb orderly occupy two tetravalent Sn sites of Ni3Sn2. This site decoration pattern of two neighboring elements, In and Sb, is unique and confirmed by first principles total energy calculations. The crystal structure can be described by two building units: Ni2Sb (building unit of Ni2In) and NiIn (NiAs-type). They alternate in the crystal structure and form infinite ac-slabs (puckered), and the slabs are stacked along [010]. A triangular lattice formed by Ni atoms indicates the existence of a geometrically frustrated structure. The calculated density of states and crystal orbital Hamilton population enlighten the stability and bonding characteristics of the structure. The temperature-dependent neutron diffraction study down to 5 K reveals that the crystal structure remains in the same orthorhombic symmetry with a weak anomaly in the lattice parameters at ∼100 K. Detailed temperature- and magnetic field-dependent magnetic properties of the title phase Ni3InSb show spin-glass- or spin-disorder-like behaviors below ∼300 K with an unusual magnetic behavior below 100 K, where an enhancement of magnetization with a decrease of the coercive field has been found.

Insight into the negative magnetization and anomalous exchange-bias in DyFe5Al7 through neutron depolarization and neutron diffraction studies

We have provided the mesoscopic and microscopic understandings of polarity reversal of the magnetization or negative magnetization (NM) below T COMP = 93 K in an exotic magnetic material containing three magnetic sublattices, viz., DyFe5Al7 crystallizing in ThMn12 structure, using neutron depolarization and neutron diffraction techniques. A full recovery of the neutron beam polarization at the T COMP in a neutron depolarization experiment reveals a total compensation of magnetization inside the magnetic domains in the sample. The temperature-dependent neutron diffraction study under zero magnetic field has provided temperature dependencies of antiparallelly coupled Dy (M Dy(2a)) and Fe (M Fe(8f) and M Fe(8j)) sublattice magnetic moments along [100] direction. The dominance of |M Dy(2a)| over total Fe moment, , below T COMP leads to the NM in the compound. The magnetization versus magnetic field curves below the T COMP indicate the presence of field-induced spin reorientation in the compound. The magnetic field required for spin reorientation (H SR) is maximum at the lowest temperature and it decreases to zero as the temperature is increased to T COMP. Interestingly, the compound shows a finite exchange-bias (H EB) below the T COMP only, as evident from the field-cooled hysteresis loops, while at T > T COMP, H EB is almost zero. The cooling-field (H COOL) dependent study of H EB shows a slope change at H COOL ∼ H SR indicating a correlation of exchange-bias with spin-reorientation in the compound. This study, apart from revealing microscopic understanding of magnetic behavior of an exotic three magnetic sublattice system, provides a correlation among exchange-bias, magnetic compensation, and spin-reorientation phenomena.

Interdependent scaling of long-range oxygen and magnetic ordering in nonstoichiometric Nd2NiO4.10

Hole doping in Nd${}_{2}$NiO${}_{4.00}$ can be either achieved by substituting the trivalent Nd atoms by bivalent alkaline earth metals or by oxygen doping, yielding Nd${}_{2}$NiO${}_{4+\delta}$. In this study, we investigated the interplay between oxygen and spin ordering for a low oxygen doping concentration i.e. Nd${}_{2}$NiO${}_{4.10}$. Although the extra oxygen doping level remains rather modest with only one out of 20 possible interstitial tetrahedral lattice sites occupied, we observed by single crystal neutron diffraction the presence of a complex 3D modulated structure related to oxygen ordering already at ambient, the modulation vectors being $\pm$2/13\textit{\textbf{a*}}$\pm$3/13\textit{\textbf{b*}}, $\pm$3/13\textit{\textbf{b*}}$\pm$2/13\textit{\textbf{b*}} and $\pm$1/5\textit{\textbf{a*}}$\pm$1/2\textit{\textbf{c*}} and satellite reflections up to fourth order. Temperature dependent neutron diffraction studies indicate the coexistence of oxygen and magnetic ordering below T${}_{N}$ $\simeq$ 48 K, the wave vector of the Ni sublattice being \textbf{\textit{k}}=(100). In addition, magnetic satellite reflections adapt exactly the same modulation vectors as found for the oxygen ordering, evidencing a unique coexistence of 3D modulated ordering for spin and oxygen ordering in Nd${}_{2}$NiO${}_{4.10}$. Temperature dependent measurements of magnetic intensities suggest two magnetic phase transitions below 48 K and 20 K, indicating two distinct onsets of magnetic ordering for the Ni and Nd sublattice, respectively.

Magnetic ordering of Ho and its role in the magnetization reversal and coercivity double peaks in the Ho3Fe5O12 garnet

Rare-earth based garnet system, Ho3Fe5O12 shows magnetization compensation phenomenon at Tcomp = 138 K and a magnetic transition at 50 K. In the present work, we reveal the physics of these low temperature magnetic transitions by carrying out detailed dc magnetization, ac susceptibility, neutron depolarization, and neutron diffraction studies. Interestingly, our dc magnetization study under low (≲ 50 Oe) magnetic fields has shown a previously unknown sign reversal of magnetization (below the Tcomp) that persists down to 5 K, the lowest measured temperature. Magnetic measurements under moderate fields between 50 Oe and 1 kOe reveal two compensation temperatures (in the range of 105 – 150 K depending upon the applied field value) leading to double magnetization reversals. Interestingly, for magnetic fields ≥ 1 kOe, these two compensation temperatures merge to a single Tcomp (=138 K). A modified Stoner-Wohlfarth model has been used to explain the asymmetrical nature of double peak around the Tcomp in the temperature dependent coercivity data. The ac susceptibility study supports the existence of both the transitions with an evidence of deep minimum at the Tcomp (138 K) and a broad peak at 50 K. Mesoscopic neutron depolarization study has revealed a zero domain-magnetization state at the Tcomp. Temperature dependent neutron diffraction study has revealed that Ho carries an induced moment above the Tcomp due to polarizing effect under the internal magnetic field of the two magnetically ordered Fe sublattices at 567 K, whereas a single umbrella type ordering of Ho sublattice moments appears below the Tcomp, resulting in the distortion of magnetic unit cell from cubic to rhombohedral symmetry. However, below 50 K, Ho3+ sites are divided into two inequivalent magnetic sublattices, having different moments and canting angles, and it leads to double umbrella type magnetic structure. Neutron diffraction study has revealed an asymmetric variation of the tetrahedral, octahedral, and dodecahedral sublattice moments resulting in a magnetization reversal at ~ 138 K which is very well supported by the mean field theory calculations. In the present study, we have resolved the ambiguity of magnetic ordering of the rare-earth (Ho3+) sublattice and its role in multiple magnetic transitions. The utility of such compensated ferrimagnetic materials in spin polarizers/analyzers and fast switching memory devices has been emphasized.

Contrasting exchange interactions in the new R3Pd5 (R = Tb, Dy, Ho, Er) compounds. Multiple magnetic transitions, spin-reorientation and frustration, as revealed by temperature dependent neutron diffraction studies: A question of sublattices?

In a recent work we have reported the formation and the crystal structure of the new family of compounds R3Pd5 (R = Sc, Y, Gd–Lu; Pu3Pd5-type, oS32, spacegroup 63, Cmcm). DFT calculations for Gd3Pd5 and heat capacity and magnetic measurements for Tb3Pd5, Dy3Pd5, Ho3Pd5 and Er3Pd5 were able to discriminate at least two distinct antiferromagnetic transitions at low temperatures; at the same time these data suggested these separate magnetic orderings to be likely associated to the two structurally different rare earth sublattices (4c and 8e, respectively). The magnetic structures of the R3Pd5 compounds, with R = Tb, Dy, Ho, Er, have been now investigated in this work. High-resolution and high-intensity neutron powder diffraction data were recorded for the four compounds of the series. The results reveal that the magnetic structures adopted are significantly diverse and their temperature dependence more complex than originally deduced from magnetic and heat capacity measurements. Tb3Pd5 is in fact the only of the four compounds where the rare earth sublattices order independently with two different magnetic propagation vectors on the two sites (k1 = [1 0 ½] for Tb2 and k2 = [kx 0 0] or k3 = [1 0 0] for Tb1). In Dy3Pd5 both sublattices follow the propagation vector k = [kx 0 0], with the second transition corresponding to a spin reorientation. In Ho3Pd5 ordering of both sublattices follow the k = [1 0 0] propagation vector; the second transition seen in the magnetic and heat capacity data corresponds to an accelerated increase in the magnetic moment of the Ho2 sublattice. The case of Er3Pd5 is special as it is the sole case where one of the rare earth sublattices does not order down to T = 1.5 K; here the second transition determined from the magnetic data corresponds to a change of the magnetic propagation vector from k1 = [kx 0 kz] to k2 = [1 0 0], both only acting on the Er2 sublattice. Irrespectively of the very similar structures not even two of the four studied R3Pd5 compounds show identical magnetic structures on either of the two sublattices. These strong variations have to be connected to changes in the RKKY interactions induced by the progressive filling of the f-orbitals of the heavy rare earth ions and the concomitant changes of the crystal electric fields.

Structural, infrared spectroscopy and magnetic properties of spinel ZnMn2O4

The polycrystalline spinel ZnMn2O4 was prepared using general solid-state reaction method. The room temperature X-ray diffraction pattern was analyzed by Rietveld refinement using FULLPROF software, which provides tetragonal symmetry with space group I41/amd. The bonds between transition metals and oxide ions in Infrared spectroscopy confirm ZnMn2O4 phase. Further, the Ńeel temperature is found to be ~297 K from our temperature dependent DC magnetic susceptibility graph, which is different from reported results. The M − H curve at 2 K confirms the formation of anti-ferromagnetic order. We further plan to carry out the temperature dependent neutron diffraction studies which will assist us in further understanding the true magnetism in this spinel oxide.

Microscopic and mesoscopic understanding of magnetization compensation phenomenon in ferrimagnetic Li0.5FeCr1.5O4 spinel

Structural and magnetic properties of the spinel compound, Li0.5FeCr1.5O4, have been investigated using dc magnetization, neutron depolarization, and neutron diffraction techniques. DC magnetization measurement at 200 Oe has revealed a ferrimagnetic ordering at 417 K and a negative magnetization state between the two compensation temperatures (TComp) of 244 and 256 K. TComp varies with an applied magnetic field and two TComp merge at 256 K for magnetic fields ≥ 500 Oe. The existence of zero domain magnetization around TComp is evident from full recovery of the transmitted neutron beam polarization in a neutron depolarization study. The Rietveld refinement of the neutron diffraction pattern at 430 K reveals that the compound possesses a face centred cubic structure with Fe0.81Li0.19 and Cr1.5Li0.31Fe0.19 as cation distributions at the tetrahedral and octahedral sites, respectively. A temperature dependent neutron diffraction study reveals that the net magnetic moment changes sign near 265 K, across the spin compensation temperature. Both neutron diffraction and mean field calculation show that an asymmetric variation of the sublattice moments as a function of temperature yields a dominance of the ordered tetrahedral site moment over the octahedral site moment below TComp, and vice versa above TComp, and gives a microscopic understanding of the observed magnetization reversal phenomenon. The achieved understanding of magnetization compensation and the high coercivity near TComp have implications for possible use of such ferrimagnetic materials with finite spin polarization as effective spin polarizers/analyzers in spintronic devices.

Spin dynamics in brownmillerite Ca2Fe1.2Al0.8O5: A temperature dependent neutron diffraction study

The crystal and magnetic structure of brownmillerite Ca2Fe2-xAlxO5; x = 0.8 has been refined against the powder neutron diffraction data collected as a function of temperature from 3 K to 350 K. Ca2Fe2-xAlxO5 is a G-type antiferromagnet with Ibm2 symmetry, the magnetic ion Fe occupies both tetrahedral and octahedral sites and both the sites are antiferromagnetically coupled individually. In this report, the mechanism of spin reorientation transition shown by these compounds is elucidated. The moment direction is found to be directed preferably along the crystallographic c-axis at low temperatures along with a small fraction of domains that are aligned along the a-axis. As the temperature is increased the domain with a-axis aligned moment inflates at the expense of domains with the moment directed along c-axis. However, at all temperatures both types of domains are found to be coexisting. The results suggest phase coexistence of the two magnetic structures with temperature dependent dynamics.

Neutron as a probe to study magnetization reversal in a spinel compound, CoCr1.9Fe0.1O4

Neutron depolarization and neutron diffraction techniques have been employed to investigate the origin of magnetization reversal in CoCr1.9Fe0.1O4 spinel compound. The spinel compound crystallizes in a face centered cubic (space group: Fd-3m) structure where Co2+ and (Cr/Fe)3+ ions occupy the tetrahedral 8a and octahedral 16d sites, respectively. The temperature dependent magnetization curves for magnetic fields ≤ 1 kOe show a magnetization reversal below the compensation temperature (Tcomp ∼ 40 K). The neutron depolarization measurements infer that the average magnetization of each domain becomes negligibly small at the TComp. Temperature dependent neutron diffraction study, a microscopic tool to understand sublattice magnetization, infers an antiparallel coupling between the tetrahedral (Co) and octahedral (Cr/Fe) site moments with ordered magnetic moments of −3.1(1) and 1.0(1) μB, respectively, at 30 K. Our neutron diffraction study also reveals that the unequal growth of the antiferromagnetically coupled tetrahedral and octahedral site moments across the TComp plays an important role in realizing the magnetization reversal in this spinel compound.

Exploring the effect of Bi doping in cubic spinel BixCo2-xMnO4 by employing neutron diffraction

The effect of Bi doping is studied in cubic spinel BixCo2-xMnO4 on their crystal as well as magnetic structure by employing neutron diffraction. Doping of nonmagnetic Bi ion at Co site make this compound more susceptible for ferroelectric properties, which have previously been established by employing XRD, magnetization, magnetodielectric, XMCD and other characterization techniques. Since neutron diffraction is a technique which can look in to microscopic aspects of crystal and magnetic structure more precisely, these series of samples are characterized by employing neutron diffraction. The room temperature neutron diffraction reveals that samples are formed in the cubic spinel structure with Fd3m (s.g. no. = 227). Magnetic structure of title compound of Co2MnO4 is scarcely studied. In order to understand the implication on the spin structure and magnetism, temperature dependent neutron diffraction study is carried out on some of the samples in the series. Earlier reported experimental finding upon Bi-doping, such as variation in the ferroelectric properties modification in magnetic properties etc. are discussed and understood in terms of variation in bond lengths and their effect on the CoO6 polyhedra.

Low-temperature neutron diffraction and magnetic studies on the magnetoelectric multiferroic Pb(Fe0.534Nb0.4W0.066)O3

We report detailed low-temperature magnetic and neutron diffraction studies on 0.8 Pb(Fe0.5Nb0.5)O3–0.2 Pb(Fe0.67W0.33)O3 which is written as Pb(Fe0.534Nb0.4W0.066)O3 (PFWN) in the general form. Magnetic susceptibility measurement data show that PFN exhibits antiferromagnetic to paramagnetic transition (T N) around 155 K (Matteppanavar et al. in J Mater Sci 50:4980–4993. doi:10.1007/s10853-015-9046-5, 2015). In the present solid solution, the magnetic susceptibility (χ) shows Neel temperature enhanced up to around 187 K. Temperature-dependent neutron diffraction studies well support the tuning up of T N from 155 to 187 K. On decreasing the temperature, for T < T N (T N = 187 K), an extra peak grows at scattering vector Q = 1.35 A−1, which indicates the onset of antiferromagnetic ordering. The observed magnetic structure is G-type antiferromagnetic with the propagation vector, k = [0.25, 0.5, 0.5]. The refined monoclinic lattice parameters (a, b and c), angle (β), unit cell volume, derivative of unit cell volume, magnetic moments and integrated intensity of magnetic peak (111) show anomaly around the T N, which is a manifestation of spin–lattice coupling. Also, the lattice parameters (a, b and c) and unit cell volume exhibit negative thermal expansion below T N and a large thermal expansion above T N.

Tetragonal to triclinic structural transition in the prototypical CeScSi induced by a two-step magnetic ordering: a temperature-dependent neutron diffraction study of CeScSi, CeScGe and LaScSi

An investigation on the ground state magnetism of CeScSi, CeScGe (tetragonal CeScSi-type, tI12, space group I4/mmm) by temperature-dependent powder neutron diffraction has been carried out, as debated and controversial data regarding the low temperature magnetic behaviours of these two compounds were reported.Our studies reveal that, while cooling, long-range magnetic ordering in CeScSi and CeScGe takes place by a two-step process. A first transition leads to a magnetic structure with the Ce moments aligned ferromagnetically onto two neighbouring tetragonal basal a-b planes of the CeScSi-type structure; the double layers are then antiferromagnetically coupled to each other along the c-axis. The transition temperature associated with the first ordering is TN ~ 26 K and TN ~ 48 K for the silicide and the germanide, respectively. Here the spin directions are rigorously confined to the basal plane, with values of the Ce magnetic moments of μCe = 0.8–1.0 μB. A second magnetic transition, which takes place at slightly lower temperatures, results in a canting of the ordered magnetic moments out of the basal plane which is accompanied by an increase of the magnetic moment value of Ce to μCe = 1.4–1.5 μB. Interestingly, the second magnetic transition leads to a structural distortion in both compounds from the higher-symmetry tetragonal space group I4/mmm to the lower-symmetry and triclinic I–1 (non-standard triclinic). Magnetic symmetry analysis shows that the canted structure would not be allowed in the I4/mmm space group; this result further confirms the structural transition. The transition temperatures TS from I4/mmm to I–1 are about 22 K in CeScSi and 36 K in CeScGe, i.e. well below the temperature of the first onset of antiferromagnetic order observed in this work (or below the ordering temperature, previously reported as either TC or TN). This result, along with the synchronism of the magnetic and structural transitions, suggests a magnetostructural origin of this structural distortion.We have also carried out powder neutron diffraction for LaScSi as a non-magnetically-ordering reference compound and compared the results with those of CeScSi and CeScGe compounds.

Low temperature magnetic studies on PbFe0.5Nb0.5O3 multiferroic

PbFe0.5Nb0.5O3 (PFN), a well-known A(B′1/2B″1/2)O3 type multiferroic, was successfully synthesized in single phase by a single step solid state reaction method. The single phase PFN was characterized through XRD, microstructure through SEM, and magnetic studies were carried out through a temperature dependent vibrating sample magnetometer (VSM) and neutron diffraction (ND) measurements. PFN exhibits a cusp at around 150K in the temperature dependent magnetic susceptibility corresponding to the Néel temperature (TN1) and another peak around 10K (TN2) corresponding to spin-glass like transition. In the temperature dependent ND studies, a magnetic Bragg peak appears at Q=1.35Å−1 (where Q=4πsinθ/λ, is called the scattering vector) below TN (150K) implying antiferromagnetic (AFM) ordering in the system. On the basis of Rietveld analysis of the ND data at T=2K, the magnetic structure of PFN could be explained by a G-type antiferromagnetic structure.

Antiferromagnetic Spin Correlations Between Corner-Shared [FeO5]7– and [FeO6]9– Units, in the Novel Iron-Based Compound: BaYFeO4

A novel quaternary compound in the Ba-Y-Fe-O phase diagram was synthesized by solid-state reaction and its crystal structure was characterized using powder X-ray diffraction. The crystal structure of BaYFeO4 consists of a unique arrangement of Fe(3+) magnetic ions, which is based on alternate corner-shared units of [FeO5](7-) square pyramids and [FeO6](9-) octahedra. This results in the formation of stairwise channels of FeO polyhedra along the b crystallographic axis. The structure is described in an orthorhombic crystal system in the space group Pnma with lattice parameters a = 13.14455(1) Å, b = 5.694960(5) Å, and c = 10.247630(9) Å. The temperature-dependent magnetic susceptibility data reveal two antiferromagnetic (AFM) transitions at 33 and 48 K. An upturn in the magnetic susceptibility data above these transitions is observed, which does not reach its maximum even at 390 K. The field-dependent magnetization data at both 2 and 300 K show a nearly linear dependence and do not exhibit significant hysteresis. Heat capacity measurements between 2 and 200 K reveal only a broad anomaly without any indication of long-range ordering. The latter data set is not in good agreement with the magnetic susceptibility data, which makes it difficult to exactly determine the magnetic ground state of BaYFeO4. Accordingly, a temperature-dependent neutron diffraction study is in order, which will enable resolving this issue. The theoretical study of the relative strengths of magnetic exchange interactions along various possible pathways, using extended Hückel spin dimer analysis, shows that only interactions between square pyramidal and octahedral centers are significant, and among them, the intrachannel correlations are stronger than interchannel interactions. This is the first physical property study in such a magnetic ion substructure.

Determination of the magnetic structure of SmFe3(BO3)4 by neutron diffraction: comparison with other RFe3(BO3)4 iron borates

Temperature dependent neutron diffraction studies were performed on SmFe3(BO3)4. The crystallographic structure was determined to stay as R32 over the whole studied temperature range of 2 K < T < 300 K. A magnetic phase transition characterized by the magnetic propagation vector κ = [0 0 3/2] takes place at TN = 34 K. The magnetic structure sees an easy-plane arrangement within the trigonal basal a–b-plane of ferromagnetic layers of iron and samarium having a canting angle of about 70° relative to each other. Neighbouring layers in the c-direction are antiferromagnetically coupled; at 2 K the magnetic moment values amount to μFe = 4.2(1) μB and μSm = 0.8(2) μB. The non-Brillouin type increase of the iron magnetic moment below TN points to a strong Fe–Sm exchange and to the simultaneous appearance of long range magnetic order on both sublattices.

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.

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 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.