The effect of a cation radii on structural, magnetic and electrical properties of doped manganites La0.6−xPrxSr0.4MnO3

Structural, magnetic and transport properties of La_0.6−xPr_xSr_0.4MnO₃ with x=0.0, 0.03, 0.06, 0.18, 0.3, 0.42, 0.54 and 0.6 are studied. The system exhibits a rhombohedrally distorted perovskite structure for x?0.3. A rhombohedral-orthorhombic (Pnma) structure transition is detected in the doping range from x=0.42 to 0.6. The structure refinement by Rietveld analysis of the X-ray powder diffraction data shows that the average distance Mn-O increases in the rhombohedral phases and decreases in the orthorhombic phases. Results show that the Curie temperature decreases from 374 to 310 K when 〈r_A〉 varies from 1.254 to 1.231 Å. Electrical measurements show that all samples exhibit a metallic to semiconducting transition with increasing temperature. Meanwhile, the size of the resistivity ρ increases near T_C. This phenomenon is interpreted as a gradual bending of the Mn-O-Mn bond angle, with decreasing 〈r_A〉, which causes the narrowing of the electronic bandwidth and the effect of the A-site variance σ².     

Crystal structure of Bi1−xTbxFeO3 from high-resolution neutron diffraction

Samples of Bi_1−xTb_xFeO₃, with x=0.05, 0.10, 0.15, 0.20 and 0.25, have been synthesised by solid state reaction. The crystal structures of the perovskite phases, characterised via Rietveld analysis of high resolution powder neutron diffraction data, reveal a structural transition from the R3c symmetry of the parent phase BiFeO₃ to orthorhombic Pnma symmetry, which is complete for x=0.20. The x=0.10 and 0.15 samples are bi-phasic. The transition from a rhombohedral to orthorhombic unit cell is suggested to be driven by the dilution of the stereochemistry of the Bi³⁺ lone pair at the A-site. The G-type antiferromagnetic spin structure, the size of the ordered magnetic moment (∼3.8 μ_B) and the T_N (∼375 °C) are relatively insensitive to increasing Tb concentrations at the A-site.     

Neutron diffraction and magnetic study of the Nd0.7Pb0.3Mn1−xFexO3 (0?x?0.1) perovskites

The effect of Fe doping on the ferromagnetic Nd_0.7Pb_0.3Mn_1−xFe_xO₃ (x=0, 0.025, 0.05, 0.075, 0.1) phases has been studied in order to analyze the double-exchange interaction. The structural and magnetic study has been carried out by neutron powder diffraction and susceptibility measurements between 1.7 and 300 K. The substitution of Fe at the Mn site results in reductions in both the Curie temperature T_c and the magnetic moment per Mn ion without appreciable differences in the crystal structures. All the compounds crystallize in Pnma space group. The thermal evolution of the lattice parameters of the Nd_0.7Pb_0.3Mn_1−xFe_xO₃ (x=0.025, 0.05, 0.075) compounds shows discontinuities in volume and lattice parameters close to the magnetic transition temperature. Increasing amounts of Fe³⁺ reduces the double exchange interactions and no magnetic contribution for x=0.1 is observed. The magnetic structures of Nd_0.7Pb_0.3Mn_1−xFe_xO₃ (x=0, 0.025, 0.05, 0.075) compounds show that the Nd and Mn ions are ferromagnetically ordered.     

Magnetostructural correlations in the antiferromagnetic Co2−x Cux(OH)AsO4 (x=0 and 0.3) phases

The Co_2−xCu_x(OH)AsO₄ (x=0 and 0.3) compounds have been synthesized under mild hydrothermal conditions and characterized by X-ray single-crystal diffraction and spectroscopic data. The hydroxi-arsenate phases crystallize in the Pnnm orthorhombic space group with Z=4 and the unit-cell parameters are a=8.277(2) Å, b=8.559(2) Å, c=6.039(1) Å and a=8.316(1) Å, b=8.523(2) Å, c=6.047(1) Å for x=0 and 0.3, respectively. The crystal structure consists of a three-dimensional framework in which M(1)O₅-trigonal bipyramid dimers and M(2)O₆-octahedral chains (M=Co and Cu) are present. Co₂(OH)AsO₄ shows an anomalous three-dimensional antiferromagnetic ordering influenced by the magnetic field below 21 K within the presence of a ferromagnetic component below the ordering temperature. When Co²⁺ is partially substituted by Cu²⁺ions, Co_1.7Cu_0.3(OH)AsO₄, the ferromagnetic component observed in Co₂(OH)AsO₄ disappears and the antiferromagnetic order is maintained in the entire temperature range. Heat capacity measurements show an unusual magnetic field dependence of the antiferromagnetic transitions. This λ-type anomaly associated to the three-dimensional antiferromagnetic ordering grows with the magnetic field and becomes better defined as observed in the non-substituted phase. These results are attributed to the presence of the unpaired electron in the dx²−y² orbital and the absence of overlap between neighbour ions.     

Structure and properties of the CaFe2O4-type cobalt oxide CaCo2O4

The calcium cobalt oxide CaCo₂O₄ was synthesized for the first time and characterized from a powder X-ray diffraction study, measuring magnetic susceptibility, specific heat, electrical resistivity, and thermoelectric power. CaCo₂O₄ crystallizes in the CaFe₂O₄ (calcium ferrite)-type structure, consisting of an edge- and corner-shared CoO₆ octahedral network. The structure of CaCo₂O₄ belongs to an orthorhombic system (space group: Pnma) with lattice parameters, a=8.789(2) Å, b=2.9006(7) Å and c=10.282(3) Å. Curie-Weiss-like behavior in magnetic susceptibility with the nearly trivalent cobalt low-spin state (Co³⁺, 3d, S=0), semiconductor-like temperature dependence of resistivity (ρ=3×10⁻¹ Ω cm at 380 K) with dominant hopping conduction at low temperature, metallic-temperature-dependent large thermoelectric power (Seebeck coefficient: S=+147 μV/K at 380 K), and Schottky-type specific heat with a small Sommerfeld constant (γ=4.48(7) mJ/Co mol K²), were observed. These results suggest that the compound possesses a metallic electronic state with a small density of states at the Fermi level. The doped holes are localized at low temperatures due to disorder in the crystal. The carriers probably originate from slight off-stoichiometry of the phase. It was also found that S tends to increase even more beyond 380 K. The large S is possibly attributed to residual spin entropy and orbital degeneracy coupled with charges by strong electron correlation in the cobalt oxides.     

Flux growth of a new cobalt-zinc-tin ternary phase Co7+xZn3−xSn8 and its relationship to CoSn

The intermetallic compound Co_7+xZn_3−xSn₈ (−0.2<x<0.2) forms from the reaction of cobalt in zinc/tin eutectic flux. This phase has a new structure type in orthorhombic space group Cmcm, with unit cell parameters a=4.138(1) Å, b=12.593(4) Å, and c=11.639(4) Å (Z=2; R₁=0.0301). Varying the amount of cobalt in the synthesis leads to formation of a superstructure in space group Pnma, with lattice parameters a=12.5908(2) Å, b=11.6298(3) Å, and c=8.2704(2) Å (Z=4; R₁=0.0347). A Co/Zn mixed site and a partially occupied Co site in the Cmcm structure order to form the Pnma supercell. TGA/DSC studies indicate that the binary phase CoSn initially forms in the flux at 1173 K, and then reacts with the zinc in the cooling solution to form the ternary structure at 823 K. This phase exhibits Pauli paramagnetic behavior.     

Synthesis, structure and electric studies for La0.7A0.3Mn0.96(InxAl(1−x))0.04O3; A=Ca and Sr perovskites

Two polycrystalline series of samples in the form La_0.7A_0.3Mn_0.96(In_xAl_(1−x))_0.04O₃; A=Ca and Sr with (0.0?x?1.0) were synthesized using solid-state reaction. Rietveld analysis of the X-ray powder diffraction showed that, the Ca-series has an orthorhombic unit cell (space group Pnma) and the Sr-series is rhombohedral with (space group ). Structural parameters (refined lattice parameters, atom positions, bond distance, bond angles, valence sum, valence bond, bond lengths and bond angles) are reported and discussed as a function of In content for the two series. Resistivity measurements in zero field are carried out in the range 50-300 K for the Ca-series and in the range 300-400 K for the Sr-series. The obtained transition temperature T_ρ at which the metal-semiconducting (MS) occurred, is discussed as a function of the compositional parameter x.     

Structure and magnetic order in the series BixRE1−xFe0.5Mn0.5O3 (RE=La,Nd)

The influence of Bi³⁺ on the structural and magnetic properties of the rare-earth-containing perovskites REFe_0.5Mn_0.5O₃ (RE=La,Nd) was studied, and the limit of bismuth substitution was determined to be x≤0.5 in Bi_xRE_1−xFe_0.5Mn_0.5O_3+δ (RE=La,Nd) at ambient pressure. Crystal structures in both La and Nd series were determined to be GdFeO₃-type Pnma with the exception of the Bi_0.3La_0.7Fe_0.5Mn_0.5O₃ sample, which is monoclinic I2/a in the a⁻b⁻b⁻ tilt scheme. The samples undergo a transition to G-type antiferromagnetic order along with a weak ferromagnetic component, mixed with cluster-glass type behavior. The substitution of bismuth into the lattice results in a drop in T_N relative to the lanthanide end-members. Long range ordering temperatures T_N in the range 240-255 K were observed, with a significantly lower ordered magnetic moment in the case of lanthanum (M∼1.7-1.9 μ_B) than in the case of neodymium (M∼2.1 μ_B).     

Structural and magnetic characterization of BiFexMn2-xO5 oxides (x=0.5, 1.0)

The title compounds have been synthesized by a citrate technique followed by thermal treatments in air (BiFe_0.5Mn_1.5O₅) or under high oxygen pressure conditions (BiFeMnO₅), and characterized by X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetization measurements. The crystal structures have been refined from NPD data in the space group Pbam at 295 K. These phases are isostructural with RMn₂O₅ oxides (R=rare earths) and contain infinite chains of Mn⁴⁺O₆ octahedra sharing edges, linked together by (Fe,Mn)³⁺O₅ pyramids and BiO₈ units. These units are strongly distorted with respect to those observed in other RFeMnO₅ compounds, due to the presence of the electronic lone pair on Bi³⁺. It is noteworthy the certain level of antisite disorder exhibited in both samples, where the octahedral positions are partially occupied by Fe cations, and vice versa. BiFe_xMn_2−xO₅ (x=0.5, 1.0) are short-range magnetically ordered below 20 K for x=0.5 and at 40 K for x=1.0. The main magnetic interactions seem to be antiferromagnetic (AFM); however, the presence of a small hysteresis in the magnetization cycles indicates the presence of some weak ferromagnetic (FM) interactions.     

Praseodymium magnetic contribution in the low temperature structure of Pr0.8Ca0.2MnO3

Magnetic and crystal structures of the manganite Pr_0.8Ca_0.2MnO₃ have been studied by neutron powder and single-crystal X-ray diffraction. Structure refinements using single crystal data [orthorhombic system, Pnma, (No. 62), a_RT=5.5534(3) Å, b_RT=7.6548(8) Å, c_RT=5.4400(5) Å, D_x=6.422 g cm⁻³, R^RT=0.029, R_w^RT=0.038] are consistent with a single domain sample. Structure and atomic displacement parameters exclude any electronic localization, even in a disordered way at 300 and 100 K. Low temperature electron diffraction observations do not show any trace of charge ordering.A Pr contribution to the magnetic structure has been shown with a maximum moment of 0.79 μ_B and spins alignments roughly along [101] orientations, at a lower temperature than the ferromagnetic transition observed at 130 K, due to Mn spins ordering.     

Magnetic properties of the chemically delithiated LixMn2O4 with 0.07≤x≤1

Magnetism for the Li_xMn₂O₄ samples with 0.07≤x≤1, which are prepared by a chemical reaction in HNO₃ solution, is investigated by direct current susceptibility (χ) and muon-spin rotation/relaxation (μSR) measurements. The effective magnetic moment (μ_eff) of Mn ions decreases monotonically with decreasing x, indicating that Mn³⁺ ions with S=2 () are oxidized to Mn⁴⁺ ions with S=3/2 () with decreasing x. On the other hand, as x decreases from 1 to 0.6, the Curie-Weiss temperature (Θ_p) increases monotonically from ∼−260 to −100 K, and then levels off to −100 K with further decreasing x. This indicates that the antiferromagnetic interaction is dominant in the whole x range. For the x=0.48 sample, the temperature dependence of χ in field-cooling mode clearly deviates from that in zero-field-cooling mode below ∼63 K (=T_m). Furthermore, the hysteresis loop is observed in the magnetization vs. field curve at 5 K. Since the zero-field μSR spectrum is well fitted by a strongly damped oscillation function, the Mn moments for the x=0.48 sample are in a highly disordered fashion down to the lowest temperature measured.     

Investigation of the quasi-ternary system LaMnO3-LaCoO3-“LaCuO3”—I: the series La(Mn0.5Co0.5)1−xCuxO3−δ

The La(Mn_0.5Co_0.5)_1−xCu_xO_3−δ series with x=0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8 and 1 was synthesized by the Pechini method to obtain insight into the phase formation in the quasi-ternary LaMnO₃-LaCoO₃-“LaCuO₃” system caused by the instability of LaCuO₃ under ambient conditions. After sintering at 1100°C some remarkable results were obtained: LaMn_0.3Co_0.3Cu_0.4O_3−δ crystallized as a single phase in the orthorhombic perovskite structure typical of LaCuO₃. Among the synthesized compositions this compound showed the highest electrical conductivity in air at 800°C (155 S cm⁻¹) and also the highest thermal expansion coefficient (α_30−800°C=15.4×10⁻⁶ K⁻¹). The LaCuO_3−δ composition also crystallized as a single phase but in a monoclinic structure although previous investigations have shown that other phases are preferably formed after sintering at 1100°C. The electrical conductivity and thermal expansion coefficient were the lowest within the series of compositions, i.e. 9.4 S cm⁻¹ and 11.9×10⁻⁶ K⁻¹, respectively.     

Structural, magnetic, and electrochemical studies on lithium insertion materials LiNi1−xCoxO2 with 0≤x≤0.25

The structural, magnetic, and electrochemical properties of the LiNi_1−xCo_xO₂ samples with x= 0, 0.05, 0.1, and 0.25 have been investigated by powder X-ray diffraction analyses, magnetic susceptibility (χ) measurements, and electrochemical charge and discharge test in non-aqueous lithium cell. According to the structural analyses using a Rietveld method, the occupancy of the Ni ions in the Li layer was estimated to be below 0.01 for all the samples and was eventually independent of x. The temperature (T) dependence of χ⁻¹ obtained with the magnetic field H=10 kOe indicated that all the samples are a Curie-Weiss paramagnet down to . At low T, all the samples entered into a spin-glass-like phase below T_f. The magnitude of T_f was found to decrease almost linearly with x, as in the case for the x dependences of the lattice parameters of a_h- and c_h-axes, Weiss temperature, and effective magnetic moment. It is, therefore, found that the change of the magnetic properties with x is simply explained by a dilution effect due to the increase of the quantity of Co³⁺ ions. On the other hand, the electrochemical measurements demonstrated that the irreversible capacity at the initial cycle is drastically decreased by the small amount of Co ions. Furthermore, the discharge capacity (Q_dis) for the x=0.05 and 0.1 samples are larger than that for the x=0 sample; namely, Q_dis=180 mAh g⁻¹ for x=0, Q_dis=217 mAh g⁻¹ for x=0.05, and Q_dis=206 mAh g⁻¹ for x=0.1. Comparing with the past results, the amount of Ni ions in the Li layer is found to play a significant role for determining the magnetic and electrochemical properties of LiNi_1−xCo_xO₂.     

Neutron diffraction studies of RSn1+xGe1−x (R=Tb-Er) compounds

The magnetic structures of RSn_1+xGe_1−x (R=Tb, Dy, Ho and Er, x≈0.1) compounds have been determined by neutron diffraction studies on polycrystalline samples. The data recorded in a paramagnetic state confirmed the orthorhombic crystal structure described by the space group Cmcm. These compounds are antiferromagnets at low temperatures. The magnetic ordering in TbSn_1.12Ge_0.88 is sine-modulated described by the propagation vector k=(0.4257(2), 0, 0.5880(3)). Tb magnetic moment equals 9.0(1) μ_B at 1.62 K. It lies in the b-c plane and form an angle θ=17.4(2)° with the c-axis. This structure is stable up to the Nèel temperature equal to 31 K. The magnetic structures of RSn_1+xGe_1−x, where R are Dy, Ho and Er at low temperatures are described by the propagation vector k=(1/2, 1/2, 0) with the sequence (++−+) of magnetic moments in the crystal unit cell. In DySn_1.09Ge_0.91 and HoSn_1.1Ge_0.9 magnetic moments equal 7.25(15) and 8.60(6) μ_B at 1.55 K, respectively. The moments are parallel to the c-axis. For Ho-compound this ordering is stable up to T_N=10.7 K. For ErSn_1.08Ge_0.92, the Er magnetic moment equals 7.76(7) μ_B at T=1.5 K and it is parallel to the b-axis. At T_t=3.5 K it tunes into the modulated structure described by the k=(0.496(1), 0.446(4), 0). With the increase of temperature there is a slow decrease of k_x component and a quick decrease of k_y component. The Er magnetic moment is parallel to the b-axis up to 3.9 K while at 4 K and above it lies in the b-c plane and form an angle 48(3)° with the c-axis. In compounds with R=Tb, Ho and Er the magnetostriction effect at the Nèel temperature is observed.     

Synthesis, structure and physical properties of the new Zintl phases Eu11Zn6Sb12 and Eu11Cd6Sb12

Reported are the syntheses, crystal structure determinations from single-crystal X-ray diffraction, and magnetic properties of two new ternary compounds, Eu₁₁Cd₆Sb₁₂ and Eu₁₁Zn₆Sb₁₂. Both crystallize with the complex Sr₁₁Cd₆Sb₁₂ structure type—monoclinic, space group C2/m (no. 12), Z=2, with unit cell parameters a=31.979(4) Å, b=4.5981(5) Å, c=12.3499(14) Å, β=109.675(1)° for Eu₁₁Zn₆Sb₁₂, and a=32.507(2) Å, b=4.7294(3) Å, c=12.4158(8) Å, β=109.972(1)° for Eu₁₁Cd₆Sb₁₂. Their crystal structures are best described as made up of polyanionic and ribbons of corner-shared ZnSb₄ and CdSb₄ tetrahedra and Eu²⁺ cations. A notable characteristic of these structures is the presence of Sb-Sb interactions, which exist between two tetrahedra from adjacent layers, giving rise to unique channels. Detailed structure analyses shows that similar bonding arrangements are seen in much simpler structure types, such as Ca₃AlAs₃ and Ca₅Ga₂As₆ and the structure can be rationalized as their intergrowth. Temperature-dependent magnetization measurements indicate that Eu₁₁Cd₆Sb₁₂ orders anti-ferromagnetically below 7.5 K, while Eu₁₁Zn₆Sb₁₂ does not order down to 5 K. Resistivity measurements confirm that Eu₁₁Cd₆Sb₁₂ is poorly metallic, as expected for a Zintl phase.     

Syntheses, crystal structures and Raman spectra of Ba(BF4)(PF6), Ba(BF4)(AsF6) and Ba2(BF4)2(AsF6)(H3F4); the first examples of metal salts containing simultaneously tetrahedral BF4 and octahedral AF6 anions

In the system BaF₂/BF₃/PF₅/anhydrous hydrogen fluoride (aHF) a compound Ba(BF₄)(PF₆) was isolated and characterized by Raman spectroscopy and X-ray diffraction on the single crystal. Ba(BF₄)(PF₆) crystallizes in a hexagonal space group with a=10.2251(4) Å, c=6.1535(4) Å, V=557.17(5) Å³ at 200 K, and Z=3. Both crystallographically independent Ba atoms possess coordination polyhedra in the shape of tri-capped trigonal prisms, which include F atoms from BF₄⁻ and PF₆⁻ anions. In the analogous system with AsF₅ instead of PF₅ the compound Ba(BF₄)(AsF₆) was isolated and characterized. It crystallizes in an orthorhombic Pnma space group with a=10.415(2) Å, b=6.325(3) Å, c=11.8297(17) Å, V=779.3(4) Å³ at 200 K, and Z=4. The coordination around Ba atom is in the shape of slightly distorted tri-capped trigonal prism which includes five F atoms from AsF₆⁻ and four F atoms from BF₄⁻ anions. When the system BaF₂/BF₃/AsF₅/aHF is made basic with an extra addition of BaF₂, the compound Ba₂(BF₄)₂(AsF₆)(H₃F₄) was obtained. It crystallizes in a hexagonal P6₃/mmc space group with a=6.8709(9) Å, c=17.327(8) Å, V=708.4(4) Å³ at 200 K, and Z=2. The barium environment in the shape of tetra-capped distorted trigonal prism involves 10 F atoms from four BF₄⁻, three AsF₆⁻ and three H₃F₄⁻ anions. All F atoms, except the central atom in H₃F₄ moiety, act as μ₂-bridges yielding a complex 3-D structural network.     

Crystal structure and magnetic properties of Na2Ni(HPO3)2

Na₂Ni(HPO₃)₂, obtained as light yellow-green crystals under mild hydrothermal conditions, crystallizes in the orthorhombic Pnma space-group with lattice parameters: a=11.9886(3), b=5.3671(2), c=9.0764(3) Å, V=584.01 Å³, Z=4. The structure consists of zig-zag chains of NiO₆ octahedra bridged by two HPO₃²⁻ and the chains are further connected through HPO₃²⁻ to four nearest chains to form a three dimensional framework, delimiting intersecting tunnels in which the sodium ions are located. The Na cations reside in the irregular Na(1)O₅, Na-O of 2.276-2.745 Å, and Na(2)O₉, Na-O of 2.342-2.376 Å, environments. The presence of the phosphite monoanion has been further confirmed by IR spectroscopy. Due to the 3D framework of Ni connected by O-P-O bridges, the magnetic susceptibility behaves as a paramagnet above 100 K (C=1.49(2) emu K mol⁻¹, μ_eff=3.45 μ_B, Θ=−39(2) K) and below 6 K, it orders antiferromagnetically as confirmed the sharp drop and the non-Brillouin behavior of the isothermal magnetization at 2 K.     

Magnetic study of two isotypic manganese chloro-sulfides: MnSbS2Cl and the new compound MnBiS2Cl

Among the MnPnQ₂X compounds (Pn: pnictide; Q: chalcogen; X: halogen), two isotypic chloro-sulfides, MnSbS₂Cl and MnBiS₂Cl, have been studied. MnBiS₂Cl is a new compound synthesized by solid state reaction at 500 °C. It is orthorhombic, space group Pnma, with a=9.502(2), b=3.8802(8), , , Z=4. Its X-ray single crystal study shows (001) waved layers of MnS₄Cl₂ octahedra, opposite edge-sharing along b, and corner-sharing along a. Similar magnetic susceptibilities for both compounds have been recorded, indicating high spin Mn²⁺ with anti-ferromagnetic exchange. Correlatively, specific heat versus temperature shows a magnetic transition at for the Sb-bearing compound, and a two-steps magnetic transition at 28 and 32 K for the Bi isotype. The magnetic structure of MnSbS₂Cl has been determined by neutron diffraction, revealing a magnetic ordering at 1.5 K with an incommensurate wave-vector along b (k=[0, 0.3838, 0]). Two modulation models, sinusoidal and helicoidal, give quite equivalent reliability factors (R_mag=0.0573 and 0.0586, respectively).     

Synthesis and magnetic properties of the quasi-one-dimensional compound Ca0.83(Cu1−xCox)O2

A new solid solution of the quasi-one-dimensional composite crystal, , has been synthesized under of O₂ at 830°C. The non-doped compound Ca_0.83CuO₂ consists of two interpenetrating monoclinic subsystems of the [Ca] atoms and the edge-shared square planar [CuO₂] chains. Upon increasing x, both the subsystems undergo a phase change from monoclinic to orthorhombic (M-O). The M-O change occurs at x∼0.04 for the [(Cu,Co)O₂] subsystem, while such a change occurs at x∼0.17 for the [Ca] subsystem. Magnetic susceptibility measurements show an evolution from a short-range ordered state near x=0 to a long-range antiferromagnetic state for the samples with x?0.15. The effective magnetic moment μ_eff is found to increase with increasing x from for x=0.10 to for x=0.30, suggesting that the solid solution can be regarded as Ca_0.83[Cu_0.66²⁺Cu_0.34−x³⁺Co_x³⁺]O₂, in which a mixed state of Cu²⁺(S=1/2), Cu³⁺(S=0) and high-spin Co³⁺(S=2) ions is realized.     

Eu doping effects on structural and magnetic properties of (Sr2−xEux)FeMoO6 compounds

Double perovskite compounds (Sr_2−xEu_x)FeMoO₆ (0≤x≤0.3) were prepared by solid-state reaction at high temperature. Crystal structure, magnetic and transport properties of the compounds were investigated. The crystal structure of the compounds changes from an I4/m lattice to an Fm3¯m lattice around x=0.1. The unit-cell volume decreases with the doping level in both the I4/m lattice and the Fm3¯m lattice. The resistivity of the compounds shows a metal-semiconductor transition, and the transition temperature T_M-S increases with the doping level. However, Curie temperature (T_C) of the compounds exhibits a weak dependence on the doping level. The saturation magnetization (M_S) at 100 K varies almost linearly with the anti-site defect concentration and agrees well with the simple FIM model. In contrast to the Ce-, Pr-, Nd- and Sm-doped Sr₂FeMoO₆, the difference of M_S of (Sr_2−xEu_x)FeMoO₆ between 5 and 100 K indicates that the moment of Eu³⁺ is antiparellel to that of Fe³⁺ at low temperature.