Search

Ni4Nb2O9 displays magnetization reversal, a particular behavior in which magnetization opposes an applied magnetic field. Previous studies have shown that this is caused by the antiferromagnetic coupling of two different layers of ferromagnetic Ni cations. In this work, magnetization reversal is controlled by the substitution of Ni by non-magnetic Zn. Ni4−xZnxNb2O9 materials with x = 0.25, 0.50, and 0.75 maintain the orthorhombic Ni4Nb2O9-type structure but display counterintuitive changes in the magnetic properties including increases in low-temperature net magnetizations, remnant magnetizations, and compensation temperatures. Furthermore, the magnetization reversal is significantly enhanced for x = 0.50 while supressed for x = 0.75, underscoring the strong effects of Zn substitution. [ABSTRACT FROM AUTHOR]

M4A2O9 transition metal oxides, with M a divalent cation and A Nb or Ta, that exhibit a structure derived from corundum constitute an interesting class of materials due to their possible magnetoelectric properties. The lack of a linear magnetoelectric effect in Ni4Nb2O9, unlike Mn4Nb2O9 or Co4Nb2O9, is explained by a comprehensive investigation, combining synchrotron x-ray and neutron diffraction with magnetization, dielectric, and polarization measurements. The m′m′m magnetic point group associated with the Pb′cn′ ferrimagnetic structure induced below 76 K by the orthorhombic Pbcn structure of Ni4Nb2O9 forbids indeed such an effect. The crystal structure and magnetic ground state of Ni4Nb2O9 are discussed and compared with those of magnetoelectric P 3 ¯ c 1 M 4 A 2 O 9 compounds whose structure derives from corundum. [ABSTRACT FROM AUTHOR]

The transport properties of the thiospinel CuCrTiS4 have been investigated in detail, focusing on the possible interplay between charges and spins, and its consequence on transport, and more specifically on the thermoelectric properties. The chemical homogeneity of a CuCrTiS4 polycrystalline sample synthesized by a direct reaction of the constitutive elements has been carefully probed by X-ray diffraction and transmission electron microscopy techniques. This thiospinel exhibits below 75 K, in its paramagnetic regime, a variable range hopping (VRH) conduction, associated with a giant magnetoresistance (MR), which persists below the spin-glass transition temperature at 8 K, reaching -95% in 9 T at 5 K. All the MR data can be rescaled as a function of H/T and described using a Brillouin function with S = 3/2. This demonstrates that the paramagnetic fluctuations strongly impact the transport properties, and this is confirmed by the Seebeck coefficient which depends on the magnetic field at low temperature, with a large negative magnetothermopower (MTEP) effect of -26% at 20 K, i.e., the thermopower is reduced as the spin alignment reduces the spin entropy. This first report of MTEP in CuCrTiS4 shows that this thiospinel behaves rather similarly to strongly correlated oxides, with MR and MTEP enhanced in the case of VRH transport with paramagnetic spins, such as in cobalt misfits or colossal MR manganites. [ABSTRACT FROM AUTHOR]

Research describing the effect of repeated thermal cycles in phase separated manganites is presented. In particular the anomalous behavior of zero field resistivity is investigated.

It has been possible to identify anomalous ferromagnetic phase induced by rhodium substitution in charge-ordered manganites Pr1-xCaxMnO3. Rh doping is less efficient than Cr or Ru doping at Curie temperatures around 100 K.

Research describing the substitution of ruthenium for manganese in doped manganites is presented. In particular the ferromagnetism and antiferromagnetism states are investigated.

The doping of the Mn sites in the antiferromagnets Ln0.5A0.5MnO3 is very efficient to induce ferromagnetism and metallicity. The effect similar to the Cr doping, differs from the latter by the fact that T(sub C0 = T(sub IM) increases significantly with the Ru level.

The structures of the Ln0.50Ca0.50MnO3 manganites (Ln = Pr, Nd, Sm, Eu and Gd) are studied using electron diffraction and lattice imaging. Results show that the tendency to form an incommensurate structure at temperatures below 92 Kelvin increases with increasing lanthanide size. A transition towards a commensurate state is also observed for the smaller cations Nd, Sm, Eu and Gd with further cooling.

The c-axis resistivity of Hg-1201 optimized crystals is studied. Results show that the c-axis resistivity values of the Hg-1201 crystals are similar to those of T1-220-1, Hg-1223 while a quasi-T-independent resistivity is observed in the normal state. It is also shown that the (CuO2) planes of Hg-1201 are coupled along c by Josephson barriers corresponding to the (BaO)-(H80.8Cu0.2Odelta)-(BaO) layers.

Two factors underlie the transition temperatures T(sub C) and T(sub N) characterizing the magnetic behavior of manganese perovskites Ln(sub 0.5)A(sub 0.5)MnO(sub 3). These factors are the average size of the A site cations and the A cations radii distribution sigma(super 2) which indicates disorder on the lattice. This was gleaned from a study of the magnetic properties of the Ln(sub 0.5)(A,A')(sub 0.5)MnO3 manganites. It is shown that sigma(super 2), aside from (r(sub A)), plays a role in the manganites' magnetic properties.

A structural and magnetoresistance investigation of layered manganites with nominal formula Ln(sub 2-y)A(sub 1+y)Mn(sub 2)O(sub 7) (Ln=Nd,Pr) (A=Ca,Sr, Ba) is conducted. A structural model where two perovskite blocks are intergrown with one rock salt type layer is suggested. The average structure crystallizes in a tetragonal unit cell. Also, an orthorhombic distortion of the tetragonal cell is observed in calcium-based oxides.

The promising thermoelectric material TiS2 can be easily chemically doped and intercalated. We present here studies of single crystals that are intercalated with excess Ti or Co, or substituted with Ta. We demonstrate the intrinsic impact of these dopants on the thermal transport in the absence of grain boundary scattering. We show that Ta doping has the greatest impact on the thermal scattering rate per ion added, leading to a five-fold reduction in the lattice thermal conductivity as compared to stoichiometric single crystals. [ABSTRACT FROM AUTHOR]

We report on the impact of zinc doping upon the magneto-electric properties of CaBaCo4O7. We show that the presence of less than 1% Zn at the Co sites decreases TC from 64K to 48K and generates two magnetic transitions, concomitant with changes of slope of dielectric permittivity, at 54K and 77 K, respectively. Powder neutron diffraction and magnetic data show the existence of an incommensurate magnetic phase and a spin-flop transition in this temperature range. The crossover of the magnetodielectric effect of this oxide, from positive below 50K to negative above this temperature emphasizes the primordial role of the incommensurate magnetic phase in the evolution of these properties. [ABSTRACT FROM AUTHOR]

A series of well sintered ceramics in the x = 0.50 - 0.60 range were used for performing a complex magnetic, structural, transport and thermal investigation of Pr(sub 1-x)Sr(sub x)MnO3 antiferromagnets. The A-type antiferromagnetic ground states in Pr(sub 1-x)Sr(sub x)MnO3 are found to be identical in the whole region of x = 0.50 - 0.60.

Research into the electric transport properties of single-crystal and ceramic supplies of Pr(sub 1-x)Sr(sub x)MnO3 perovskites is presented. It was found that the charge carrier transport in the C-type antiferromagnets is reliably characterized by variable range hopping along the ferromagnetic chains.

Dense ceramics of the itinerant ferromagnet CoS2 have been prepared by the spark plasma sintering technique. The structural study confirms a cubic unit-cell for CoS2 with a = 5.539(6)Å ([formula]). Scanning and transmission electron microscopy reveal the existence of sulfur deficient regions of composition 'Co2S3' with a structure compatible to that of CoS2 where 0.5 S atom are missing in one out of two successive layers along the b direction. The volume of these regions estimated to be less than 1% is explained by possible S losses from the surface during the sintering. The physical properties measurements show a high TC (122 K), large saturated magnetization (0.88 μB/f.u.), with a ∼100% magnetoresistance at 5 K in 9 T. Also, the value of the residual resistivity ratio, ρ300 K/ρ5 K = 45, between those of crystal and conventional ceramics, attest for both good compacity and grain connectivity. Interestingly, the Seebeck coefficient exhibits negative values reaching S = -47.5 μV K-1 at 675 K and below TC, S can be fitted by a diffusion model with a magnon term related to the ferromagnetism. A large power factor (S2/ρ) of 1 mW m-1 K-2 is obtained over a broad T range but the too high thermal conductivity (κ675 K ∼ 8.7 W K-1 m-1) is a limiting physical parameter to use CoS2 ceramics in thermoelectric devices. [ABSTRACT FROM AUTHOR]

Research using insulating charge ordered magnanite Pr0.6Ca0.4MnO3 to study the doping of a manganese site with M=Fe3+, Al3+, Ga3+, Ti4+, Sn4+ and Mg2+ shows that The magnanite exhibits a canted CE-type magnetic structure. Charge ordering in doped manganite Pr0.6Ca0.4Mn1-xMxO3 becomes non-existent when when x is greater than or equal to 0.02. Ferromagnetic metallic state transition occurs when M=Fe3+, Al3+, ga3+ and Mg2+. Tetravalent cation doping has little effect on phase magnetic and transport properties.

In this paper, the dimensionless figure of merit (ZT) is optimized using the scattering in nanocrystals (NCs) of Zr-doped In2O3-δ. The effect of boundary scattering on the thermoelectric properties of the NCs was analyzed using the Boltzmann transport equation and Debye-Callaway model. A ZT map computed based on these theories determined the optimum material parameters to improve the transport properties of the NCs. A theoretically predicted enhancement in ZT of ∼40% can be reproduced experimentally, indicating that engineering of ZT using NCs is promising. [ABSTRACT FROM AUTHOR]

Bulk ceramics In2-xMxO3, with a metal-like behavior, have been synthesized in air for M=Ti4+, Zr4+, Sn4+, Ta5+, and Nb5+, with rather low solubility limits xℓ, ranging from 0.01 to 0.1. An abrupt increase in the electrical conductivity and of the carrier concentration with x is observed in the monophasic region (xℓ), whereas in the biphasic region (x>xℓ) these values do not vary significantly. These results show that the valence of the doping element plays a crucial role in such properties, similar to degenerated semiconductors. Similarly, the thermopower |S| value is correlated with this evolution decreasing as x increases for xℓ. For the Sn doped samples, the maximum carrier concentration n=10.8×1020 cm-3 and electrical conductivity σ=5×103 S cm-1 are both achieved at x=0.06–0.1 (∼3–5 at. %) for a thermopower S of -20 μV/K at room temperature. In comparison, the minimum |S| and maxima σ and n of In2O3 compounds doped with the other cations occur at lower doping levels, e.g., xℓ∼0.02 and xℓ∼0.015 for Ti and Zr/Nb/Ta doped In2O3, respectively. The relationship between the values of room temperature Hall mobility and carrier concentration shows that numbers and/or effects of multicharged scattering centers of electrons are different depending on the doping element. In2O3 doped with M(IV) elements shows maximum values of mobility close to x=0.006, whereas the doping with M(V) cations induces a decrease in the Hall mobility even for small doping levels. The thermoelectric performances are significantly improved at these low doping levels, with ZT values close to 0.3 at 1000 K in the doped materials against 0.1 mW/mK2 for the undoped phase. [ABSTRACT FROM AUTHOR]

The thermoelectric properties of air-prepared cosubstituted indium oxide based compounds belonging to the series In2-2xMxSnxO3 (M=Zn, Cu, or Ni) have been studied. X-ray diffraction studies show that the solubility limit xmax increases from xmax=0.35 for M=Cu to xmax=0.45 for M=Zn and xmax=0.55 for M=Ni. The lattice parameters, following the Vegard law with increasing substitution rates are in good agreement with the divalent oxidation state for the M cations. Compared to the undoped In2O3 prepared in air, the electrical resistivity of the cosubstituted phases (M=Zn,Cu) is strongly decreased and exhibits a metallic behavior. A more complex behavior is observed for the Ni/Sn cosubstituted samples whose resistivity first decreases and then increases with x. The lowest resistivity values do not exceed 0.5 mΩ cm at room temperature. Despite the lower values of the thermopower in cosubstituted samples, the thermoelectric power factor is significantly higher than that of the undoped In2O3, leading to values exceeding 5.10-4 W m-1 K-2. Furthermore, as the lattice thermal conductivity is strongly reduced by the cosubstitution due to mass fluctuation scattering of the phonons, promising thermoelectric figure of merit ZT is observed, close to 0.3 at 1273 K in In1.6Zn0.2Sn0.2O3. Thus, this study emphasizes the important role of cosubstitution to improve the thermoelectric properties of these n-type oxides. [ABSTRACT FROM AUTHOR]

Magnetic properties of polycrystalline Sm0.1Ca0.9-yBayMnO3 (y=0.02, 0.06) samples have been investigated in the temperature range of 2–320 K, magnetic fields of up to 90 kOe, and under hydrostatic pressures of up to 12 kbar. It was found that the volume fraction of ferromagnetic (FM) phase at 5 K is about 27% for Sm0.1Ca0.88Ba0.02MnO3 and only ∼1% for Sm0.1Ca0.84Ba0.06MnO3. The compound Sm0.1Ca0.88Ba0.02MnO3 exhibits magnetic phase separation below TN≈TC≈99 K, which is consistent with a model of FM clusters embedded in antiferromagnetic (AFM) G-type matrix. For this sample, magnetization and ac susceptibility exhibit a cluster glasslike behavior below TC, while the resistivity exhibits pronounced thermal hysteresis around TC, indicating upon a plausible first order magnetic phase transition. For Sm0.1Ca0.84Ba0.06MnO3 two peaks observed in the temperature dependence of the ac susceptibility at low temperatures may be related to magnetic transitions, associated with the C- and G-AFM structures. Both, a significant hysteresis of magnetization observed at T<100 K and an increase in magnetoresistance at low temperatures are apparently an indicative of magnetic field induced structural transformation from monoclinic to orthorhombic phase. This transformation occurs concurrently with magnetic transition from C-type AFM to G-type AFM structure. It was found that an applied pressure enhances TC of Sm0.1Ca0.88Ba0.02MnO3 with a pressure coefficient dTC/dP≈0.6 K/kbar. The spontaneous FM moment of Sm0.1Ca0.88Ba0.02MnO3 decreases by 15% under pressure of about 12 kbar, while under the same pressure it only slightly increases for Sm0.1Ca0.84Ba0.06MnO3. For both samples, the paramagnetic Curie temperature decreases under pressure indicating upon an increase in AFM interactions. Stronger suppression of the FM phase for the sample with y=0.06, in comparison with that one for 0.02 sample, is attributed to the effect of the chemical disorder, playing a more significant role than the effect related to the changes in A>. [ABSTRACT FROM AUTHOR]

The Bi–Sr–Co–O system has been investigated for small bismuth contents in order to study the formation of the misfit oxide series built up from the stacking of three rocksalt-type layers (n=3) with a single CdI2-type CoO2 hexagonal layer. Starting from nominal compositions, written as [Sr2Co1-xBixO3]RS[CoO2]1.8 (x=0.1, 0.2, 0.3, 0.4, and 0.5), samples have been synthesized and their structure has been analyzed by combining transmission electron microscopy techniques and powder x-ray diffraction data. For x≈0.5, intergrowths are clearly observed, made of a majority of triple (n=3) and a few quadruple (n=4) rocksalt-type layer-based misfit cobaltites. Transport measurements (2.5 up to 320 K) reveal that the Bi introduction reduces the resistivity, especially at room temperature. Furthermore, the thermopower (Seebeck coefficient S) of such intergrowth (S≈120 μV K-1 at 300 K) is found to be of the same order as the one measured for the n=4 Bi–Sr cobaltite while the resistivity (ρ≈20 mΩ cm at 300 K) is significantly reduced in comparison with the same compound. [ABSTRACT FROM AUTHOR]

The substitution of barium and strontium for calcium in the pseudo-charge exchange (CE)-type charge ordered manganite Pr0.6Ca0.4MnO3 has been reinvestigated for low substitution levels (<10%). It is shown that Ba or Sr substitution exhibits a greater ability to induce ferromagnetism, metallicity and sharp magnetization, and resistivity multisteps at low temperature (2.5 K) in this phase, than in the CE-type manganite Pr0.5Ca0.5MnO3. The crucial role of the size of the A-site impurity is emphasized, the larger Ba2+ cation being much more efficient than Sr2+ to induce such effects. This study demonstrates that the multistep-like behavior, previously observed for Mn-site substitution in Pr0.6Ca0.4MnO3, can be obtained by A-site substitution, Ba substitution being as efficient as Cr substitution, and Sr substitution having a similar effect to Ga substitution. In the framework of the martensitic mechanism, it is suggested that the introduction of larger cations on the Ca sites, or of non-Jahn–Teller cations on the Mn3+ sites, induces “locally” around them the formation of more symmetric domains within the distorted antiferromagnetic matrix. This structural phase separation would induce the electronic phase separation, favoring the formation of ferromagnetic metallic regions in the antiferromagnetic insulating matrix. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Substitutions in the Mn sublattice of antiferromagnetic, charge, and orbitally ordered manganites was recently found to produce intriguing metamagnetic transitions consisting of a succession of sharp magnetization steps separated by plateaus. The compounds exhibiting such features can be divided into two categories, depending on whether they are sensitive to thermal cycling effects or not. One compound in each category has been considered in the present study. This article reports on the influence of two treatments: high-temperature annealing and grinding. It is shown that both of these treatments can dramatically affect the phenomenon of magnetization steps. The results provide us with information about the origin of these jumps in magnetization. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The isovalent substitution of Ca[sup 2+] for Sr[sup 2+] substitution in the recently discovered misfit cobaltite [Pb[sub 0.7]Co[sub 0.3]Sr[sub 2]O[sub 3]] [CoO[sub 2]] [sub 1.79] has been investigated for its very attractive thermopower properties. Starting from the pure Sr cobaltite with a thermopower S value at 300 K in the range from 100 to 130 µV K[sup -1], it is found that the calcium substitution enhances the thermopower value up to + 165 µVK[sup -1] for the pure calcium phase, [Pb[sub 0.4]Co[sub 0.6]Ca[sub 2]O[sub 3] [CoO[sub 2][sub 1.61]. Since these thermoelectric materials are studied for the high T applications, it should be pointed out that this S improvement induced by chemical substitution is even more pronounced for T ... 300 K with S[sub 700] K = + 210 µV K[sup -1]. This beneficial effect is interpreted in the light of the clear modification in the geometry of CoO[sub 2] layers which could play a role on the cobalt electronic configurations. [ABSTRACT FROM AUTHOR]

Ca[sub 3-χ]Sr[sub χ]Co[sub 4]O[sub 9] (χ = 0,0.5,1.0) samples were prepared by solid state reaction. As expected from the radii of Sr[sup 2+] and Ca[sup 2+], the cell parameters increase with Sr content χ. Simultaneously, the resistivity and the carrier localization at low temperature are enhanced. The thermoelectric power is not sensitive to the Sr content. Furthermore, the ferromagnetism at low temperature becomes weaker with the increase of Sr content, which shows that antiferromagnetism and ferromagnetism compete in these cobaltites. Large Sr content enhances antiferromagnetic interactions, which can be related to the extending plateau of magnetoresistance ratio of ρ(H)/ρ(0) in the low magnetic field region. [ABSTRACT FROM AUTHOR]

Substitutions at the Mn site by cations M with oxidation states higher than 4+, such as Mo[sup 6+] and Ru[sup 5+], are shown to stabilize SrMn[sub 1-χ]M[sub χ]O[sub 3] cubic perovskite manganites. This effect is explained by the induced Mn valency shift, which corresponds to electron doping by Mn[sup 3+] in the Mn[sup 4+] matrix. Interestingly, these electron-doped manganites, characterized by large A-site cationic size, exhibit coupled structural, magnetic, and transport transitions close to or beyond 300 K for M = Ru[sup 5+] and M = Mo[sup 6+], respectively. These transitions are characteristic of the d[sub z²] orbital ordering generally associated with C-type antiferromagnetism. This result contrasts with the inhomogeneous ferromagnetic metallic state induced by Ru in CaMnO[sub 3]. The possibility to induce orbital/charge ordering in CaMn[sub 1-χ]MO[sub χ]O[sub 3] or orbital ordering in SrMn[sub 1-χ]M[sub χ]O[sub 3] (M = Ru, Mo) with M contents superior to 10% makes it more difficult to explain based on long-range cooperative Jahn-Teller phenomena in mixed-valency manganites. [ABSTRACT FROM AUTHOR]

The effect of ruthenium doping upon the appearance of metallicity and ferromagnetism in the series Sm[sub 1-x]Sr[sub x]MnO[sub 3] is studied and compared with that previously observed for Sm[sub 1-x]Ca[sub x]MnO[sub 3]. It is shown that, in both cases, Ru doping is efficient in the region where charge ordering exists at long or short range, T[sub C] increasing significantly with the doping level. In contrast, in the antiferromagnetic electron-rich region of the Sm[sub 1-x]Sr[sub x]MnO[sub 3] series (x>0.6), which does not show charge ordering, no ferromagnetism is obtained by Ru doping, though T[sub N] is decreased. It is concluded that the huge effect of Ru doping in the appearance of ferromagnetism and metallicity originates from its ability to hinder the underlying charge and orbital ordering, allowing double exchange to be restored. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The doping of Mn sites of the A-type antiferromagnet Pr[sub 0.5]Sr[sub 0.5]MnO[sub 3] with ruthenium shows that ferromagnetism and metallicity are induced similarly to the doping of the CE-type phases Ln[sub 0.5]Ca[sub 0.5]MnO[sub 3]. This effect, similar to the Cr doping, differs from the latter by the fact that T[sub C]=T[sub IM] increases significantly with the Ru level. The different behaviors of Ru and Cr doped Pr[sub 0.5]Sr[sub 0.5]MnO[sub 3] samples are interpreted on the basis of two factors, ferromagnetic superexchange introduced by the magnetic dopants, and valency effect which contributes to increase the Mn[sup 3+] content for Ru(IV) and Ru(V) and does the opposite for Cr(III). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Bulk ceramics [In.sub.2-x][M.sub.x][O.sub.3], with a metal-like behavior, are prepared in air for M = [Ti.sup.4+], [Zr.sup.4+], [Sn.sup.4+], [Ta.sup.5+], and [Nb.sup.5+], with low solubility limits. The relationship between the values of room temperature Hall mobility and carrier concentration has shown that numbers and effects of multicharged scattering centers of electrons are different depending on the doping element.

The thermoelectric properties of air-prepared cosubstituted indium oxide based compounds belonging to the series [In.sub.2-2x][M.sub.x][Sn.sub.x][O.sub.3] are studied. The analysis has stressed the vital role of cosubstitution to improve the thermoelectric properties of these n-type oxides.

The temperature range of 2-320 K, magnetic fields of up to 90 kOe and hydrostatic pressures of up to 12 kbar were used to analyze the magnetic properties of polycrystalline [Sm.sub.01.][Ca.sub.0.9-y][Ba.sub.y]Mn[O.sub.3] samples. The hysteretic effects exhibited by the resistivity of compound in the vicinity of critical temperature [T.sub.C], indicated the first order magnetic transition, a remarkable feature for electron doped manganites.

An electron magnetic study of electronic and magnetic ordering induced by Ru doping was carried out in polycrystalline [La.sub.0.4][Ca.sub.0.6][Mn.sub.1-x][Ru.sub.x][O.sub.3] samples. Results revealed that the magnetic ground state of the compound remains definitely inhomogeneous due to the magnetic ground state due to the existence of ferromagnetic and anitferromagnetic phases up to at least, x=0.10.

The Bi-Sr-Co-O system is investigated for small bismuth contents to study the formation of the misfit oxide series built up from the stacking of three rocksalt-type layers (n=3) with a single CdI2-type CoO2 hexagonal layer. The clear relationship between the Bi content and both resistivity value and existence of a thermoelectric power enhancement is discussed with respect to the structural features.

A study on the electron magnetic-resonance (EMR) probing of the changes in the magnetic structure of a CaMn(sub 1-y)Mo(sub y)O3 system during Mo doping of the Mn sites is presented. The results indicate that a strong difference is observed between the resonant properties of Mo- and Ru doped series at both paramagnetic and magnetically ordered states.

The magnetization avalanches under field are investigated at low temperature in Pr(sub 0.50)Ca(sub 0.50)Mn(sub 1-x)Ni(sub x)O (x=0.05). The ultrasharp steps observed in the low-temperature isothermal magnetization and resistivity curves are investigated by neutron power diffraction in magnetic fields up to 5 T.

The study is conducted to reinvestigate the multi-step like behavior of magnetization, which was obtained by A-site substitution in Pr(sub 0.6)Ca(sub 0.4)MnO(sub 3) and is similar to the Mn-site substitution in Pr(sub 0.6)Ca(sub 0.4)MnO(sub 3). Barium and strontium substitution have the ability to induce ferromagnetism in manganites and are able to generate ultrasharp steps in magnetization and resistivity.

The ferromagnetic regions were induced with the layered (A-type) antiferromagnet (AFM) Pr(sub 0.44)Sr(sub 0.56)MnO3 by substitution of the Mn sites and their effects of the magnetoresistive properties were analyzed. Irrespective of the ratio of magnetic phases, the samples exhibit a nonmetallic behavior of resistivity and thermopower, pointing to the nanoscopic nature of the phase separation.

The inhomogeneous magnetic states in electron-doped Ca(sub 1-x)Sm(sub x)MnO3 (0 less than x less than or equal to 0.2) are analyzed by magnetic resonance methods at x=0.2 and by a qualitative modeling due to De Gennes. It was seen that the spontaneous magnetization in Ca(sub 1-x)Sm(sub x)MnO3 increases nonlinearity with x and at increasing concentration, the model becomes restricted to a part of the doped electrons associated with impurity center.

The thermal cycling effect in Pr0.5Ca0.5Mn0.97Ga0.03O3, which decreases the saturation magnetization and increases the characteristic fields of the jumps is discussed. The study strongly supports the relevancy of a martensic-like transformation induced by the external magnetic field application invoked to explain the sharp magnetization steps feature observed in the Mn site doped PS OO/Co perovskite manganites.

Presents information on a study which investigated the colossal magnetoresistance properties of the manganese perovskites lanthanum[sub0.7-x]yttrium[subx]calcium[sub0.3] manganese oxygen[sub3-δ]. Experimental procedure; Results and discussion; Conclusion.

The effect of Sr(super 2+) substitution for Ca(super 2+) on the structure, transport properties, and magnetic properties is discussed. The ferromagnetism at low temperature becomes weaker with the increase of Sr content, which shows that antiferromagnetism and ferromagnetism compete in these cobaltites.

The perovskite manganite Pr0.65Ca0.21Sr0.14MnO3 prepared as single crystal and ceramic specimens have studied using magnetic, transport, and thermal measurements. All samples are identical metallic ferromagnets with T(sub c)=204 K, nontheless unusual thermal hysteresis of magnetic susceptibility, electrical resistivity, and thermoelectric power.