Average Cation Radius Research Articles

Influence of Gd-content on the electrical transport properties of La0.67−x Gd x Sr0.33MnO3 polycrystalline ceramics by sol–gel method

Polycrystalline perovskite manganites La0.67−x Gd x Sr0.33MnO3 (x = 0.15, 0.20, 0.25, 0.30, 0.35, and 0.40) were prepared by sol–gel method. The crystal structure examined by X-ray powder diffraction indicates that the samples were single phase and crystallize in a rhombohedral structure with increasing Gd content. The grain size and surface morphology were investigated by scanning electron microscope, which reveals that that all the ceramic samples with better crystallization have high density. The relation between resistivity and temperature studied by the standard four-probe method shows that the metal–insulator transition temperature (T P) shifts to the lower temperature and temperature coefficient of resistivity decrease with increasing Gd doping. It is mainly due to Gd doping decreases the A-site average cationic radius 〈r A〉 and thus the Mn3+–O–Mn4+ angle decrease, which result in the reduction of double exchange between Mn3+ and Mn4+.

High pressure structural phase transitions in Ho: Eu2O3

Structural stability and phase transitions in mixed rare earth sesquioxides (Eu1−xHox)2O3 crystallizing in the cubic bixbyite structure were investigated under high pressure using angle dispersive X-ray diffraction technique. Studies on various compositions of the mixed oxide show that when the average cationic radius, RRE (where, RRE = xRHo+(1−x)REu) is equivalent to or below 0.9164 Å, the system undergoes a cubic to monoclinic transition as a function of pressure, whereas, when RRE equivalent to or above 0.9220 Å it is observed to prefer a transition from cubic to hexagonal structure. Based on our detailed investigations, a pressure-concentration (P−x) phase diagram for (Eu1−xHox)2O3 up to a pressure of 15 GPa is constructed. The bulk moduli for the parent and high pressure phases are calculated from the Birch-Murnaghan equation of state fit to the experimental pressure volume data and are reported. Structural analysis based on refinement has revealed that, an increasing structural rigidity of the cubic phase with decreasing RRE leads to an increase in the transition pressure and bulk moduli except for 0.4 ≤ x ≤ 0.6. The observed significant reduction in bulk moduli and transition pressure for 0.4 ≤ x ≤ 0.6 is due to the increased micro strain/internal pressure developed upon doping.

Tuning room temperature Tp and MR of La1-y(Cay-xSrx)MnO3 polycrystalline ceramics by Sr doping

Polycrystalline Sr−doped La1-y(Cay-xSrx)MnO3 (LCSMO, y=3/8) ceramics with x=0, y/25, 2y/25, 3y/25, 4y/25, y/3, y/2, and 2y/3 were prepared by sol−gel methods. X-ray diffraction patterns results indicated that all the bulk samples were single phase without any impurities. The structure of the samples transformed from orthorhombic phase (space group of Pnma) to rhombohedral phase (space group of R3̅c) when the Sr content (x) was equal to or greater than y/2. With the increasing of x content, the temperature coefficient of resistance (TCR) and magnetic resistance (MR) decreased gradually. However, the metal to insulator transition temperature (Tp) and the MR reached at 300.4K and 12% at 300K for the LCSMO (x=4y/25) sample, respectively, which meant the LCSMO material could be used as a candidate for photoelectric (uncooled bolometer or infrared detectors, etc.) or magnetic devices (uncooled magnetic sensors, etc.) at room temperature. Visibly, the results indicated that the room temperature modulation of Tp and MR was observed when the site of the Ca2+ ion was substituted by the Sr2+ ion in LCSMO (y=3/8) polycrystalline ceramics. This gave rise to the increasing size of the A−site average cationic radius <rA> and improving of the Mn4+ ion concentration through double exchange between the Mn3+ and Mn4+ ions, leading to enhance the electrical and magnetic properties of LCSMO ceramics.

Structural, spectral, dielectric and magnetic properties of Ni0.5MgxZn0.5-xFe2O4 nanosized ferrites for microwave absorption and high frequency applications

Ni0.5MgxZn0.5−xFe2O4 (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) (NiMgZn) nano-sized ferrites were synthesized via sol-gel route. The average cation radius, bond lengths (A and B sites), shared (dAE, dBE) and unshared edges (dBEU) of the NiMgZn nanoferrites were determined from the XRD data. FTIR studies confirmed the spinel structure of NiMgZn nanoferrites. The force constant at tetrahedral and octahedral sites were calculated. The surface morphology was investigated from the micrographs. The dielectric parameters such as dielectric constant, dielectric loss factor, loss tangent and Q values with different concentration of Mg in NiZn nanoferrite were evaluated. It was found that the NiMgZn sample at x=0.5 showed high Q values with low dielectric losses at higher frequencies. The squareness ratio and coercivity values confirmed the super paramagnetic behaviour of the NiMgZn nano-sized ferrites. However, the saturation and remanence increased with the increasing Mg contents whereas coercivity values follow the Stoner-Wolforth model for NiMgZn at x=0, 0.2, 0.3 and 0.4. The NiMgZn nano-sized ferrites samples at x=0.1 and 0.5 show the variations in coercivity values which may be due to the strong LS coupling and super-exchange interactions of the metal cations at tetrahedral and octahedral sites. The dielectric and magnetic studies of NiMgZn nano-sized ferritesexplored their application in various technological and industrial fields such as magnetic storage, microwave absorption and high frequency applications.

Fabrication of La x Nd0.67−x Sr0.33MnO3 polycrystalline ceramics by sol–gel method

A systematic experimental study for La x Nd0.67−x Sr0.33MnO3 polycrystalline ceramic samples (x = 0.00, 0.07, 0.08, 0.09, 0.1, 0.2 and 0.3) were prepared by sol–gel method. The crystal structures were analyzed by X-ray diffraction, which reveals that all the samples are single-phase without any detectable secondary phases. The grain size and surface morphology were investigated by scanning electron microscope, which indicates that the ceramic samples with better crystallization have high density and chemical uniformity. The relation between resistivity and temperature shows that the resistivity decreases and the metal–insulator transition temperature shifts to higher temperature with the substitution La ion for Nd ion, which gives rise to increasing transition broadening temperature, and consequently decreases the temperature coefficient of resistivity. It is mainly due to the substitution La for Nd increases the A-site average cationic radius and thus the Mn–O–Mn angle increases, which gives rise to the double exchange between Mn3+ and Mn4+.

Crystallographic and Spectroscopic Investigations on Nine Metal–Rare‐Earth Silicates with the Apatite Structure Type

AbstractNine silicates with the apatite structure type (space group P63/m) containing both rare‐earth elements (REEs: Pr, Nd, Sm, Tb, Ho and Er) and various metals (K, Sr, Ba and Cd) were synthesised by high‐temperature flux‐growth techniques and characterised by single‐crystal X‐ray diffraction, scanning electron microscopy, Raman spectroscopy and laser‐induced photoluminescence spectroscopy. In all of the compounds, the 6h Wyckoff position is predominantly or solely occupied by REE3+ cations, whereas the cations shows a mixed occupancy at the larger, nine‐coordinate 4f site with 55–75 % of REE3+ cations and 45–25 % of other metal cations. The O4 (“free” oxygen) site is fully occupied by O2– anions, except for a Ba–Pr member with full occupancy by F– anions. The refined formulas are Cd2Er8(SiO4)6O2, Cd2Tb8(SiO4)6O2, KHo9(SiO4)6O2, KTb9(SiO4)6O2, KSm9(SiO4)6O2, Sr2Nd8(SiO4)6O2, Ba2Nd8(SiO4)6O2, Ba2Sm8(SiO4)6O2 and Ba4Pr6(SiO4)6F2. Changes in the metaprism twist angle (φ) and correlations between the unit‐cell parameters, average cationic radii (of M+/M2+–REE3+ pairs) and the chemistry of both the synthesised M+/M2+–REE3+ silicate apatites and those reported previously are evaluated. Photoluminescence measurements of undoped samples yielded emission bands in the visible region from green to red; therefore, these compounds are potential candidates for luminescent materials.

Solid solutions and phase transitions in (Ca,M2+)M2+Si2O6 pyroxenes (M2+ = Co, Fe, Mg)

The effect of the substitution of Ca with Co, on the phase transition and on the extension of the miscibility gap, was studied to model the general mechanism of phase transitions and solid solutions in (Ca,M 2+ )M 2+ Si 2 O 6 pyroxenes. Eleven pyroxenes with composition Ca 1−x Co 1+x Si 2 O 6 , (0 ≤ × ≤ 1) were therefore synthesized by piston cylinder at P = 3 GPa, and T between 1100 and 1350 °C. The samples were characterized by SEM-EDS, XRD powder diffraction, and TEM. The results were compared with those of Ca-Fe and Ca-Mg pyroxenes. The phase diagram of Ca-Co pyroxenes is similar to that of Ca-Fe and Ca-Mg ones, with a wide asymmetric miscibility gap, and higher solubility in the Ca-rich side of the gap. The solubility on the Ca-rich side of the gap is related to the radius of the cation substituting. The cell parameters of the Ca-Co pyroxenes undergo a sudden change at the composition of about 0.4 Ca apfu, due to the C 2/ c – P 2 1 / c phase transition. The change in volume with composition follows an ideal trend, in the C 2/ c phase, dictated by the ionic size of the substituting cation. Deviation from the C 2/ c behavior are instead observed in the P 2 1 / c field and ascribed to volume strain. The same turnover was found in Ca-Mg, Ca-Fe, and Ca-Mn pyroxenes. The C 2/ c – P 2 1 / c transition occurs with decreasing the M2 average cation radius, down to a critical value between 0.85 and 0.88 A, depending on the series. A stabilization of the C 2/ c phase related to crystal field in Ca-Fe and Ca-Co pyroxenes is suggested by the analysis of the volume strain in the P 2 1 / c field. A key finding is that a miscibility gap may develop either by lattice strain related to cation substitution, within a series where all end-members have the same structure, or for the combined effect of lattice strain and a phase transition, as is the case for pyroxenes.

The ordering degree and thermal conductivity in the pyrochlore-type composition systems with a constant cation radius ratio

A2B2O6O'-type pyrochlore compounds with a constant average cation radius ratio (r(A3+)/r(B4+)=1.5), (Gd1−xLnx)2(Zr1−yTiy)2O6O' (Ln: Nd, La), were synthesized by solid state reaction at 1600°C for 10h. The ordering degree and thermal conductivity of the ceramics were investigated. XRD and Raman results revealed that all the ceramics exhibited pyrochlore phase but different ordering degree. Compared with B-site substitution in Gd2Zr2O7, A-site substitution led to higher ordering degree and lower thermal conductivity when the value of r(A3+)/r(B4+) kept at a constant. The lowest thermal conductivity could be obtained by both A-site and B-site substitutions.

Thermochemistry of Barium Hollandites

Barium hollandites, a family of framework titanates that can potentially be used for the immobilization of short‐lived fission products (especially 137Cs) in radioactive wastes, have been investigated by high‐temperature oxide melt solution calorimetry using 2PbO·B2O3 solvent at 702°C. The enthalpies of formation from constituent oxides show increasing energetic stability of the hollandite phase as Ti4+ is substituted by Mg2+, Al3+, and Fe3+, in that order. In general, the thermodynamic stability increases with decreasing average cation radius in the β sites, and when the tolerance factor approaches one. The Al‐ and Fe‐hollandites are more stable than phase assemblages containing BaTiO3 perovskite and Al/Fe/Ti oxides, whereas Mg‐hollandite is less stable than the corresponding assemblage of BaTiO3 perovskite, MgTiO3 ilmenite, and TiO2. This instability makes Mg‐hollandite a less suitable host for fission products. Hollandite phase formation during metal citrate combustion synthesis depends more on thermodynamic stability and phase chemistry than on the annealing temperature.

Synthesis and Structural Characterization of the La0.7A0.3MnO3 (A=Sr,Ca,Ba and Na) Nanocrystalline Powders Prepared by a Simple Thermal Decomposition Route

Nanocrystalline powders of a manganite compound in the series of La0.7A0.3MnO3 (LA3M), where A is Ca2+, Na1+, Sr2+ or Ba2+ are synthesized by a simple thermal decomposition method using related acetate salts as starting materials in aqueous solution. The precursors are analyzed by Thermogravimetric/Differential Thermogravimetric Analyzer (TG-DTG) techniques and then all of synthesized nanopowders are characterized at room temperature using X-ray diffraction (XRD) and X-ray absorption fine structure (EXAFS) techniques. The initial structural characterization shows that all the prepared samples exhibit non-stoichiometric perovskite structures. Only the La0.7Na0.3MnO3 (LN3B) sample contains oxygen deficiencies, whereas most samples contain excess oxygen, which results in cation vacancies in either the A- or B-site. The three regions of the crystal-structure transition are observed with variation of the average cationic radius in the A-site (〈rA〉). The orthorhombic structure is observed when a smaller cation (Ca2+) is substituted for La3+. Likewise, the cubic structure is only obtained after substitution by the much larger Ba2+ ion, whereas the rhombohedral structure is still exhibited after substitution by Na1+ and Sr2+. The different structures are affected by the ionic radii of the A ion and the Mn4+ ion. Jahn–Teller distortions in the MnO6 octahedra composed of unequal \(d_{\mathrm{Mn}\mbox{--}\mathrm{O}}\) in two or three bond lengths is observed for all samples except the LB3M sample, which exhibits equal \(d_{\mathrm{Mn}\mbox{--}\mathrm{O}}\) values. The increasing of 〈rA〉 can decrease this MnO6 distortion by shrinking the \(d_{\mathrm{Mn}\mbox{--}\mathrm{O}}\) in the long bonds and stretching the \(d_{\mathrm{Mn}\mbox{--}\mathrm{O}}\) in the short bonds; the distortion begins to vanish as 〈rA〉≥1.292 A.

Structural and kinetic study of phase transitions in LaYSi2O7

Abstract Phase transitions in LaYSi 2 O 7 have been investigated as a function of temperature using XRD, NMR and TEM. Previously described empirical crystal structure guidelines based on average cation radius in rare-earth RE 2 Si 2 O 7 -type disilicates predict a stable tetragonal A-LaYSi 2 O 7 polymorph at temperatures below 1500 °C. This study demonstrates that A-LaYSi 2 O 7 is not thermodynamically stable at these temperatures and suggests that guidelines based on average cation size do not accurately describe the equilibrium behaviour of this silicate system. The A to G-type polymorph transition is extremely sluggish; complete transformation requires ∼250 h at 1200 °C, and more than 3 weeks of calcination at 1100 °C. This observation is important when this type of material is used as environmental barrier coating (EBC) of advanced ceramics. Analysis of XRD and TEM data reveal complete substitution of Y and La on the rare-earth cation sites in both LaYSi 2 O 7 polymorphs, but indicate preferential site occupancies in the G-type polymorph.

Co-substitution at the Mn-site in YMnO3: Structural stability and physical properties

The YMnO3 oxide, crystallizing in the P63cm space group is one of the most studied multiferroic material. While these properties can be modified by substitutions at the Mn-site, the peculiar fivefold coordination appears to limit the M solubility range in YMn1−xMxO3. This motivated the preparation by solid state reaction of several series of co-substituted YMn1−x(M′,M″)xO3, which were studied using both powder X-ray diffraction and transmission electron microscopy. The cation pairs have been chosen for their ability to adopt a fivefold coordination similar to that of Mn3+ in YMnO3, to keep a constant average trivalent oxidation state and to maintain an average cationic radius similar to that of Mn3+. For YMn1−x(Cu1/2Ti1/2)xO3, a complete solid solution is observed without cation ordering. For all other studied cation pairs, the solubility range is always reaching a minimum value of 25% for the Zn containing pairs (Zn2/3V1/3 and Zn3/4Mo1/4), a maximum of 50% being reached for the Cu containing pairs (Cu2/3V1/3, Cu2/3Nb1/3 and Cu3/4W1/4). Interestingly, the non-centrosymmetric P63cm space group is retained within the solubility range without generating cation ordering phenomena. These co-substitutions at the Mn3+ are found to induce a decrease of the antiferromagnetic ordering temperature, the TN variations being similar to the temperature decrease of the dielectric anomaly. Thus, these oxides are interesting candidates for the study of the multiferroic behavior of YMnO3 derivatives.

Octahedral tilting, monoclinic phase and the phase diagram of PZT

Anelastic and dielectric spectroscopy measurements on PbZr1−xTixO3 (PZT) close to the morphotropic (MPB) and antiferroelectric boundaries provide new insight into some controversial aspects of its phase diagram. No evidence is found of a border separating monoclinic (M) from rhombohedral (R) phases, in agreement with recent structural studies supporting a coexistence of the two phases over a broad composition range x < 0.5, with the fraction of M increasing toward the MPB. It is also discussed why the observed maximum of elastic compliance appears to be due to a rotational instability of the polarization linearly coupled to shear strain. Therefore it cannot be explained by extrinsic softening from finely twinned R phase alone, but indicates the presence also of M phase, not necessarily homogeneous. A new diffuse transition is found within the ferroelectric phase near x ∼ 0.1, at a temperature TIT higher than the well established boundary TT to the phase with tilted octahedra. It is proposed that around TIT the octahedra start rotating in a disordered manner and finally become ordered below TT. In this interpretation, the onset temperature for octahedral tilting monotonically increases up to the antiferroelectric transition of PbZrO3, and the depression of TT(x) below x = 0.18 would be a consequence of the partial relief of the mismatch between the average cation radii with the initial stage of tilting below TIT.

Crystal structure and properties of a new mixed-valence compound LiMn 2TeO 6 and the survey of the LiMM′XO 6 family (X = Sb or Te)

A new compound, LiMn 2+Mn 3+TeO 6, was prepared by solid-state reactions and characterized by powder X-ray diffraction, redox titration, conductivity, magnetic measurements and cycling behaviour in an electrochemical cell with Li counter electrode. It is triclinic, P1, a = 5.1077(1), b = 8.5707(1), c = 5.0589(1), α = 92.515(1)°, β = 92.092(2)°, γ = 89.818(2)°, Z = 2. The structure is based on strongly distorted hexagonal close packing of oxygen anions with cations occupying octahedral voids and represents the ordered variant of orthorhombic Li 2TiTeO 6 structure, derived from LiSbO 3. TeO 6 octahedra are almost regular but all four independent MnO 6 octahedra display severe distortions. Room-temperature conductivity is unexpectedly low for a mixed-valence compound, 2 × 10 −7 S/cm. Together with the observed antiferromagnetic exchange interaction, this is a prerequisite for the colossal magnetoresistance effect. The unit cell volumes of LiMn 2TeO 6, LiSbO 3, Li 2M 4+TeO 6 and LiMM′XO 6 series (a total of 21 compounds) correlate well with average cationic radii, but LiMn 2SbO 6 deviates considerably, and its preparation could not be reproduced.

High-pressure displacive phase transition of a natural Mg-rich pigeonite

A high-pressure single-crystal X-ray diffraction study has been carried out on a P21/c natural Mg-rich pigeonite sample with composition ca. Wo6En76Fs18 using a diamond anvil-cell. The unit-cell parameters were determined at 14 different pressures to 7.14 GPa. The sudden disappearance of the b-type reflections (h + k = odd) and a strong discontinuity (about 2.8%) in the unit-cell volume indicated a first-order P21/c–C2/c phase transition between 4.66 and 4.88 GPa. The P(V) data of the P21/c phase were fitted to 4.66 GPa by a third-order Birch–Murnaghan equation of state (BM3 EoS), whereas the limited number of experimental data collected within the C2/c phase between 4.88 and 7.14 GPa were fitted using the same equation of state but with K′ constrained to the value obtained for the P21/c fitting. The equation of state coefficients are V0 = 424.66(6) A3, KT0 = 104(2) GPa and K′ = 8(1) for the P21/c phase, and V0 = 423.6(1) A3, KT0 = 112.4(8) GPa, and K′ fixed to 8(1) for the C2/c phase. The axial moduli for a, b, and c for the P21/c phase were obtained using also a BM3-EoS, while for the C2/c phase only a linear calculation could be performed, and therefore the same approach was applied for comparison also to the P21/c phase. In general the C2/c phase exhibits axial compressibilities (βc > βa >> βb) lower than those of the P21/c phase (βb > βc ≈ βa; similar to those found in previous studies in clinopyroxenes and orthopyroxenes). The lower compressibility of the C2/c phase compared with that of the P21/c could be ascribed to the greater stiffness along the b direction. A previously published relationship between Pc and M2 average cation radius (i.r.) has been updated using all the literature data on P21/c clinopyroxene containing large cations at M2 site and our new data. The following weighted regression was obtained: Pc (GPa) = 26(4) − 28(5) × i.r (A), R2 = 0.97. This improved equation can be used to predict the critical pressure of natural P21/c clinopyroxene samples just knowing the composition at M2 site.

Study of the formation temperature of mixed LaREO3 (RE ≡ Dy, Ho, Er, Tm, Yb, Lu) and NdGdO3 oxides

Mixed LaREO3 (RE ≡ Dy, Ho, Er, Tm, Yb, Lu) and NdGdO3 oxides were prepared by thermal decomposition of the corresponding co-precipitated mixed oxalates. The decomposition of La/RE and Nd/Gd oxalates was studied by means of differential thermal analysis and thermogravimetric (DTA-TG) measurements; in particular the last step, consisting of the loss of a CO2 molecule from the corresponding oxycarbonate, has been thoroughly investigated, as it is particularly interesting for the study of the formation temperature of mixed rare earth oxides. After the release of CO2, the oxides crystallize in a distorted perovskitic cell or one of the structures typical of rare earth sesquioxides, depending on the cationic size difference and on the average cationic radius. The mixed rare earth oxycarbonate decomposition has been studied in comparison to the decomposition of single rare earth oxycarbonates. A trend of the mixed oxides formation temperature as a function both of the average cationic size and of the cationic sizes difference has been observed and compared to the behaviour of single rare earth oxides.

Short-range ordering state and cluster-glass behavior in electron-doped manganite [formula omitted

In this paper, we investigated the electrical and magnetic properties of electron-doped manganite Y 0.4Ca 0.6MnO 3 with a relatively small average cationic radius 〈 r A 〉 . The small 〈 r A 〉 of the present system results in a short-range antiferromagnetic charge-ordering (AFM-CO) state in the manganite. With the decrease of temperature, a ferromagnetic super-exchange interaction begins to establish itself between the remaining disordered Mn ions after the formation of the short-range CO state. Then, a reentrant cluster-glass state originates from the frustration between the FM order in the clusters and the AFM interactions present in the background matrix.

Magnetic properties of RE0.7Ca0.3Mn0.95Fe0.05O3 (RE=Sm and Gd) manganites at low temperature

The magnetic properties of RE 0.7 Ca 0.3 Mn 0.95 Fe 0.05 O 3 perovskite with rare-earth cations (RE=Sm and Gd) were investigated by means of X-ray diffraction, Mössbauer spectroscopy, and low temperature (4.2–266 K) magnetization measurements. Structural characterization of these compounds shows that they both have orthorhombic (Pbnm) structure. The Mössbauer spectra show clear evidence of local structural distortion of the Mn(Fe)O 6 octahedron, which is based on the non-zero nuclear quadrupole interactions for high-spin Fe 3+ ions. It was found that the local structural distortion increases significantly when Sm 3+ is replaced by Gd 3+ . This distortion is attributed to the Jahn–Teller coupling strength as estimated from the Mössbauer effect results. The magnetic results indicate that the Curie temperature decreases as a result of replacing Sm by Gd. This is due to the decrease of the average A-site cationic radius 〈 r A 〉. The rapid increase of magnetization at low temperature indicates the magnetic ordering of rare earth ions at the A-site.

Order–disorder phase transformations in quaternary pyrochlore oxide system: Investigated by X-ray diffraction, transmission electron microscopy and Raman spectroscopic techniques

Order–disorder transformations in a quaternary pyrochlore oxide system, Ca–Y–Zr–Ta–O, were studied by powder X-ray diffraction (XRD) method, transmission electron microscope (TEM) and FT-NIR Raman spectroscopic techniques. The solid solutions in different ratios, 4:1, 2:1, 1:1, 1:2, 1:4, 1:6, of CaTaO 3.5 and YZrO 3.5 were prepared by the conventional high temperature ceramic route. The XRD results and Rietveld analysis revealed that the crystal structure changed from an ordered pyrochlore structure to a disordered defect fluorite structure as the ratios of the solid solutions of CaTaO 3.5 and YZrO 3.5 were changed from 4:1 to 1:4. This structural transformation in the present system is attributed to the lowering of the average cation radius ratio, r A/ r B as a result of progressive and simultaneous substitution of larger cation Ca 2+ for Y 3+ at A sites and smaller cation Ta 5+ for Zr 4+ at B sites. Raman spectroscopy and TEM analysis corroborated the XRD results.

Cluster-glass state and the effect of A-site magnetism in electron-doped manganites

The magnetic properties of Y 0.35Ln 0.05Ca 0.6MnO 3 (Ln = La, Pr, Nd, Sm, Gd, Dy) have been investigated thoroughly. The small average cationic radius 〈 r A 〉 of the present system results in a short-range antiferromagnetic charge-ordering (AFM-CO) state in the manganites. With the decrease of temperature, a super-exchange interaction begins to establish itself between the remaining disordered Mn ions after the formation of the short-range CO state. Then, the reentrant cluster-glass state originates from the frustration between the FM order in the clusters and the AFM interactions present in the background matrix. However, the large magnetic moments of Gd 3+ and Dy 3+ ions apply an internal magnetic field on the Mn 3+ and Mn 4+ ions, which results in the suppression of the cluster-glass state.