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This paper reports the observation of hexagonal phase of barium titanate by Mn doping and its effect on dielectric and magnetic properties. Ceramic samples of Ba 0.98 Zn 0.02 Ti 1− x Mn x O 3 (where, x = 0.04, 0.06 and 0.08) were prepared by traditional solid-state reaction route. The hexagonal phase is stabilized in the composition Ba 0.98 Zn 0.02 Ti 0.92 Mn 0.08 O 3 and a very feeble M – H loop is also observed in that composition. This induced magnetism is expected due to the exchange interactions between magnetic polarons formed by oxygen vacancies with Mn ions. The dielectric constant as well as the ferroelectric to paraelectric transition temperature is systematically decreased with increasing of Mn doping concentration. Further to that, the temperature dependent dielectric constant curve is also broadened at transition temperature with increasing of Mn concentration. However, the ferroelectric to paraelectric transition temperature is well above room temperature. [ABSTRACT FROM AUTHOR]

Ceramic samples of BaTi 0.95− x Hf 0.05 Co x O 3 (where, x =0.05, 0.1, and 0.15) were prepared through a solid state reaction route and structure, morphology, magnetic and ferroelectric properties have been investigated. Defects play a key role in influencing magnetic as well as the electric properties in the above compositions. Magnetism observed in doped compositions is significantly depended upon Co ion concentration and oxygen vacancies. With increasing of Co ion concentration, the concentration of oxygen vacancies is increased and as a result of which enhanced magnetic effect is observed. The presence of oxygen vacancy forms defect-dipoles with Co and Hf. These defect-dipoles prominently influenced the polarization and coercive field in doped compositions. Although remnant polarization is decreased noticeably in doped compositions, but the ferroelectricity is observed well above room temperature. These results clearly demonstrate the importance of the contribution of defects for observation of room temperature multiferroic properties in Co based BaTiO 3 ceramics. [ABSTRACT FROM AUTHOR]

Abstract: We report the observation of room temperature magnetism and ferroelectricity in polycrystalline BaTi0.95−x Hf0.05Co x O3 ceramics, where x=0.05, 0.1, and 0.15. Magnetic and ferroelectric hysteresis loops are strongly influenced by Co ion doping concentration. Magnetization of doped compositions is enhanced with increasing of Co ion concentration. Room temperature ferromagnetism is also observed in BaTi0.8Hf0.05Co0.15O3. Simultaneously, the saturation electric polarization value is decreased with the increasing of Co ion doping concentration. Our XPS results have revealed the presence of oxygen vacancies in doped samples. Oxygen vacancies have significant influence on magnetic and ferroelectric properties of doped BaTiO3. Observation of room temperature magnetism in our samples may be due to the exchange interactions of cobalt ions through oxygen vacancies. [Copyright &y& Elsevier]

Abstract: Crystalline solid solution of BiHo X Fe1+X O3 (X=0, 0.05, 0.1, and 0.15) ceramics have been successfully synthesized by slow step sintering schedule. At particular value of X (X=0.1) the sample showed good crystallinity with almost impurity free phases. It was observed that at particular concentration of X (X=0.1), the sample showed enhanced M–H loop by Ho doping in presence of excess Fe. Furthermore, the M–H loop gets reduced with the increase in value of X (X=0.15). Compared to the pure BFO, the dielectric properties for X=0.1 composition are improved due to the decreased oxygen vacancies by the stabilized oxygen octahedron. Raman spectra over the frequency range of 100–1500cm−1 have been systematically investigated with different concentrations of X. Besides the changes of the peak position and the line width of the all modes, the prominent frequency shift, the line broadening and variation of the intensity for the two-phonon mode between 1270 and 1280cm−1 were observed with increase in value of X. All these results indicate the existence of strong spin–phonon coupling in Ho doped Fe rich BFO. [Copyright &y& Elsevier]

Abstract: Bi1+x Ce x FeO3 (Ce–BFO) for x=0, 0.05, 0.1, and 0.15 monophasic ceramic samples were successfully synthesized by conventional solid-state reaction routes. The influences of Ce doping on structural, dielectric, ferroelectric, leakage current and capacitive properties of BiFeO3 ceramics were investigated intensively. At higher concentrations of x (x=0.1 and 0.15) the samples showed good crystallinity with almost impurity free phases. No structural phase transformation took place after partial doping of Ce ions and all ceramic bulk samples remain in their rhombohedral structure with space group R3c. The dielectric behavior of the samples improved significantly and the ferroelectric hysteresis loops changed their shape from rounded to a strongly nonlinear typical ferroelectric feature mainly originating from the domain switching and became enhanced with increase in doping concentration of cerium (Ce). Experimental results also suggested that partial doping of higher valence, smaller ionic radius Ce ions in BiFeO3 forces the reduction of oxygen vacancies, resulting in a great suppression of leakage current. It is found that the sharp capacitance peak/discontinuity present in the C–V characteristics of Ce–BFO for different Ce doping concentrations is directly associated with the polarization reversal. Incorporation of excess bismuth in the presence of Ce in BiFeO3 is expected to compensate Bi loss during high temperature sintering and caused structural distortion which also favors enhancement of ferroelectric properties in Ce-doped BFO. [Copyright &y& Elsevier]

Abstract: Room temperature multiferroic electroceramics of Gd doped BiFeO3 monophasic materials have been synthesized adopting a slow step sintering schedule. Incorporation of Gd nucleates the development of orthorhombic grain growth habit without the appearance of any significant impurity phases with respect to original rhombohedral (R3c) phase of un-doped BiFeO3. It is observed that, the materials showed room temperature enhanced electric polarization as well as ferromagnetism when rare earth ions like Gd doping is critically optimized (x=0.15) in the composition formula of Bi1+2x Gd2x/2Fe1−2x O3. We believe that magnetic moment of Gd+3 ions in Gd doped BiFeO3 tends to align in the same direction with respect to ferromagnetic component associated with the iron sub lattice. The dielectric constant as well as loss factor shows strong dispersion at lower frequencies and the value of leakage current is greatly suppressed with the increase in concentration of x in the above composition. Addition of excess bismuth and Gd (x=0.1 and 0.15) caused structural transformation as well as compensated bismuth loss during high temperature sintering. Doping of Gd in BiFeO3 also suppresses spiral spin modulation structure, which can change Fe–O–Fe bond angle or spin order resulting in enhanced ferromagnetic property. [Copyright &y& Elsevier]

Abstract: This paper aims to report that impurity phase free single phase multiferroic BiFeO3 ceramic can be prepared by critically optimizing the metal ion concentration using slow step sintering schedule at 850°C for 24h. Antiferromagnetic character of pure BiFeO3 is completely changed and ferromagnetic behavior observed with increase of Bi as well as decrease of Fe concentration. It is found that Bi rich (Bi: 1.2) Fe deficient (Fe: 0.8) composition produces single phase rhombohedral structure with space group R3c along with enhanced ferroelectric and ferromagnetic properties. Incorporation of excess bismuth caused structural distortion and expected to compensate Bi loss during high temperature sintering. On the other hand, iron deficient helps the formation of Fe3+ state, which hinders the creation of oxygen vacancies and also favors the reduction of leakage current. Structural distortion in BiFeO3 changes Fe–O–Fe bond angle or spin order, destructs the spin cycloid and releases a locked magnetization. [Copyright &y& Elsevier]

A simple low cost novel synthesis method was developed to prepare nanosized La0.67Ca0.3MnO3 (LCMO) without any requirement of a calcinations step at high temperature. Powders synthesized by a new chemical technique were fine and nano-sized with high purity perovskite structure. The size and topography of the oxides are dependent on the calcinating temperature of the precursors. The resulting particle size is in the range of 20 to 100 nm as determined by transmission electron microscopy. The magnetization of LCMO nanophase is strikingly dependent on the particle size. The sample prepared from 600°C calcined sample sintered at 1200°C for 4 hour shows metal-to-insulator transitions at around 265 K. Bulk LCMO prepared from these powders shows excellent structural, magnetic and magneto-transport properties. [ABSTRACT FROM AUTHOR]

Abstract: We have developed a simple low-cost novel synthesis route to synthesize nanosized La0.7Sr0.3MnO3 (LSMO) without any requirement of a calcinations step at high temperature. The study of these nanoparticles indicates excellent properties (magnetization and resistance at 0T) similar to colossal magnetoresistance (CMR) materials sintered at 1600°C for 20h. The size and topography of the oxides are dependent on the calcinating temperature of the precursors. The resulting particle size is in the range of 20–100nm as determined by transmission electron microscopy. The magnetization of LSMO nanophase is strikingly dependent on the particle size. The transition temperature from the paramagnetic to ferromagnetic state of the sample is quite sharp and occurs at 372K for 600°C calcined sample sintered at 1200°C for 4h. Magnetoresistance of magnitude −5.7% at the field up to 1T was also observed at room temperature. [Copyright &y& Elsevier]

We report on the processing and characterization of high performance epitaxial manganite films grown on SrTiO3 and SrTiO3 buffered MgO substrates with a Tc tailored to room temperature. We have demonstrated that La1-xBaxMnO3 and La1-xSrxMnO3 epitaxial films on SrTiO3 buffered MgO substrate show significantly improved transport and magnetization properties in the vicinity of room temperature on ex situ annealing at 900 °C. Our results suggest that manganite films can be grown on either SrTiO3 or SrTiO3 buffered MgO substrates which can serve as template layer to integrate manganites onto appropriate semiconductors for device applications. [ABSTRACT FROM AUTHOR]

Abstract: Cobalt (Co) doped HoMnO3 (HMO) bulk ceramics having structural formula HoMn1−x Co x O3 (x=0, 0.025, 0.05, 0.1) are prepared using a conventional solid state reaction route and the effect of Co substitution at Mn site for the improvement of its structural, dielectric and multiferroic properties is studied. Optimizing the dopant concentration of Co (x=0.1), hexagonal phase (P63cm) of HMO is completely transformed to orthorhombic (Pbnm) structure. From magnetic measurement, it is observed that incorporation of Co atoms into HMO shows low temperature ferromagnetic behavior around 10K and its origin is attributed to the double exchange interaction between Mn3+- and Mn4+ ions. The materials also exhibit a sharp dielectric anomaly well above the room temperature around 530K at the concentration of x=0.1. Shifting of both magnetic transition as well as dielectric anomaly curve towards higher temperature is a clear indication for the existence of strong correlation between magnetic and electric dipole ordering. From XPS spectrum, it is found that oxidation state of Co atoms is +2 state and Mn atoms are both in +3 and +4 mixed state. [Copyright &y& Elsevier]

Abstract: Our paper reports structural, magnetic and ferroelectric properties of Ni doped barium titanate. Ceramics samples of BaTi1−x Ni x O3 (here, x=0, 0.05, 0.1, and 0.15) were prepared through solid state sintering technique. It is revealed from structural studies that the phase transformation from tetragonal to hexagonal phase is strongly influenced by Ni doping concentration. Magnetism is induced in doped composition and the value of magnetism is dependent upon Ni ion concentration. This enhanced magnetic effect is likely to originate from carrier-mediated exchange interactions. Ferroelectricity was observed in all samples at room temperature, but it was decreased by Ni doping. [Copyright &y& Elsevier]

Polycrystalline Zn 1-x Cr x O (0.01 ≤ x ≤ 0.09) samples synthesised by solid state reaction technique were sintered at different temperatures following slow step sintering schedule, investigated for optical and magnetic properties using suitable characterisation techniques. Cr 2 O 3 and CrO 2 phases have been detected in the Raman spectra of Zn 1 -x Cr x O samples with x ≥ 0.05. Photoluminescence study indicated improved optical property of the samples compared to undoped ZnO. While low percentage Cr doped samples show diamagnetic behaviour, different types of magnetic orderings are observed in the samples with higher percentage of dopants (x ≥ 0.05) for different sintering temperatures. The spin system and magnetic properties were analysed through Electron Spin Resonance study; g-value of 1.97 indicates Cr in 3+ valence state in ZnO. Presence of both Cr3+ and Cr4+ in ZnO understood to facilitate super exchange interactions to promote room temperature ferromagnetism. ESR study ensures improved magnetic homogeneity through slow step sintering process. [ABSTRACT FROM AUTHOR]

We have optimized Gd ion substitution in BiFeO 3 (BFO) and observed prominently change in structural, electrical and magnetic behavior of Bi 1+2x Gd 2x/2 Fe 1−2x O 3 ceramics synthesized through slow step sintering schedule. It is observed that with the increase in concentration of Gd (x=0.1), original structure of BFO is transformed from rhombohedral R 3 c space group to orthorhombic Pn 21 a space group. Surprisingly, unit cell volume is drastically contracted (35% for x=0.2) and the sintered specimen showed enhanced room temperature ferromagnetic behavior although the original BFO is normally G-type antiferromagnetic in nature at 643 K. It is expected that intrinsic chemical pressure within the bulk body built by the substitution of Gd in presence of excess bismuth greatly supported through unidirectional movement of electrical dipole moment with in each individual domain as a result of which suppression of leakage current with enhanced dielectric and ferroelectric hysteresis is observed. [ABSTRACT FROM AUTHOR]

The effect of sintering temperature on structural, electrical and magnetic behaviours of polycrystalline samples of Ho0.9Ca0.1Mn0.9Co0.1O3 prepared by the solid state reaction route sintered at three different temperature 1250°C, 1350°C, 1450°C for 10h are investigated. XRD, SEM, magnetization, dielectric and ferroelectric measurements were carried out. Experimental results showed the nucleation of orthorhombic phase as the sintering temperature increases from 1250°C to 1450°C. Ferroelectric (T c ) and antiferromagnetic transition temperature (T N ) increases with increase in sintering temperature. Strong bifurcation of FC and ZFC curve in sample sintered at 1450°C showed a clear onset of ferromagnetic state around 165°K, which is confirmed from M to H graph at 165°K. All the sample showed ferroelectric behaviour at room temperature which are leaky in nature. Sintering temperature along with Ca and Co doping in HoMnO3 ceramics plays an important role in phase transformation along with enhancement in multiferroic properties. [ABSTRACT FROM AUTHOR]

This paper reports the effect of sintering temperature on ferroelectric properties of GdMnO3 (GMO) bulk ceramics at room temperature prepared by the conventional solid state reaction route following slow step sintering schedule. Ferroelectric hysteresis loop as well as sharp dielectric anomaly in pure (99.999%) GMO sintered ceramics has been clearly observed. Samples sintered at 1350°C become orthorhombic with Pbnm space group and showed frequency independent sharp dielectric anomalies at 373K and a square type of novel ferroelectric hysteresis loop was observed at room temperature. Interestingly, dielectric anomalies and ferroelectric behavior were observed to be dependent upon sintering temperature of GdMnO3. Room temperature dielectric constant (ε r ) value at different frequencies is observed to be abnormally high. The magnetic field and temperature dependent magnetization show antiferromagnetic behavior at 40K for both 1350°C and 1700°C sintered GMO. Present findings showed the possibility of application of GdMnO3 at room temperature as multifunctional materials. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the paramagnetic behavior of Mn doped ZnO co-doped with rare earth (Gd and Sm) atoms. The formation of secondary rare earth oxides (Gd2O3 and Sm2O3) is confirmed from the X-ray diffraction patterns. The rare earth oxides in the system forbids the grain growth and interconnection between the grains. The weak link between the grains suppresses the long range exchange interaction between the Mn ions and hence, reduces the ferromagnetic ordering. Owing to the large mismatch between ionic radii of rare earth and transition metal atoms inside the matrix, the rare earth element cannot contribute to promote ferromagnetic behavior in Mn doped ZnO, irrespective of their high individual magnetic moments. [Copyright &y& Elsevier]

Abstract: We have observed good ferroelectric loops at room temperature in hexagonal HoMnO3 (HMO) bulk ceramics sintered at 1250°C. Microstructure and ferroelectric hysteresis loops are observed to be dependent on sintering temperature. It is observed that with an increase of sintering temperature, hexagonal a-axis is compressed and c-axis is marginally dilated with overall contraction of the hexagonal unit-cell volume. We explain the origin of ferroelectricity through relative movement of Ho ion and Mn ion within its unit-cell volume, resulting in the distortion of unit-cell volume. We argue that ferroelectric origin of hexagonal HMO at room temperature may be due to the marginal displacement of Ho ion along a-axis, that influences the exchange interaction among the Mn3+ and Ho3+ ions, causing magnetically induced ferroelectricity at room temperature. [Copyright &y& Elsevier]

Abstract: Mn-doped ZnO samples having composition Zn1−x Mn x O (x=0.02, 0.04 and 0.05) were synthesized by solid state reaction technique with varying concentration of Mn from 0.02 to 0.05. Evidence of room temperature ferromagnetism was observed only in the composition Zn0.98Mn0.02O sintered at 500°C. Our XRD pattern confirms the presence of Mn3O4 impurity phase in all the Zn1−x Mn x O samples with the exception of Zn0.98Mn0.02O. We emphasize that the appearance of Mn3O4 phase in the system forbids the exchange type of interaction between the Mn ions and suppresses the ferromagnetism in all the Mn over-doped Zn1−x Mn x O (x>0.02) system. SEM microstructure study also supports the interruption of exchange type of interaction inside the system with the increase in Mn concentration in the sample. Interestingly, for this particular composition, Zn0.98Mn0.02O sintered at 500°C, glassy ferromagnetism type of transition is observed at low temperature. This type of transition is attributed to the formation of the oxides of Mn clusters at low temperature. [ABSTRACT FROM AUTHOR]

Abstract: Enhancement in room temperature ferromagnetism has been observed in Mn doped ZnO, when co-doped with Ni. In the co-doped system, Ni–O–Ni and Ni–O–Mn carrier mediated exchange interaction dominates the Mn–O–Mn exchange interaction which causes a fair increase in the value of saturation magnetization at room temperature. It is believed that the simultaneous doping of Ni and Mn onto ZnO increases the carrier concentration in form of clusters of oxygen vacancies and hence favors the carrier mediated exchange interaction for the enhancement of magnetic moments in the system. [Copyright &y& Elsevier]

Abstract: A clean signature of room temperature multiferroicity in Bi1.2Gd0.1Fe0.8O3 ceramics is observed. Samples were prepared by slow step sintering technique at 850°C. Impurity peaks normally present in original BiFeO3 are completely suppressed with the increase of Bi concentration. Apart from this, structural transformation took place from R3 C to Pn21 a space group and a clear orthorhombic grain growth habit is seen by SEM microstructure. Suppression of impurity phases favors the reduction of mobile oxygen vacancies and hence reduces leakage current for which ferroelectric properties of Bi1.2Gd0.1Fe0.8O3 are enhanced. We argue that the addition of Gd is likely to suppress the spiral spin modulation and at the same time increase the canting angle which favors the enhanced ferromagnetism. Excess Bi is expected to act as point defects and occupy interstitial positions which in turn surrounded by oxygen vacancies and is likely to promote defect driven ferromagnetism with enhanced spin and electric polarization. This finding encourages further revaluation of long-discounted BiFeO3 for multiferroics research. [ABSTRACT FROM AUTHOR]

Abstract: We report our novel result regarding the observation of unusual but clean ferromagnetic (FM) signature at room temperature (RT) in high pure (99.999%) ZnO bulk ceramics processed by slow step sintering schedule (SSSS). All the sintered samples showed ferromagnetic signature at room temperature. However, sample sintered at 850°C showed more prominent M–H loop and saturation magnetization with respect to samples sintered at 500°C and 1300°C. Observation of FM behavior in sintered ceramics may be attributed to the presence of defects like cation (Zn)/anion (O) vacancies and interstitials created during the processing of sample. It is anticipated that SSSS promotes enhanced physical bulk as well as surface densification and at the same time confined the outgassing of free oxygen and Zn from the bulk which are acting as suitable defect sites inside the sintered grains and grain boundary junctions. Our micro-Raman and X-ray photoelectron studies revealed the existence of these defects which are believed to be the origin of the unconventional ferromagnetism (FM) of ZnO bulk ceramic at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports that defect driven magnetism can be obtained at room temperature by optimizing metal ion concentration in bismuth ferrite (BFO) following our novel slow step solid state sintering route. We observed a clean signature of enhanced multiferroic behavior in Gd doped bismuth ferrite (Gd-BFO) bulk ceramics at room temperature (RT). Bismuth rich iron deficient Gd-BFO ceramics were prepared by solid state route through slow step sintering schedule at 850°C. At particular composition, (Bi1.2Gd0.1Fe0.8O3), this materials completely transform from rhombohedral R3c to orthorhombic Pn21a space group. We emphasized that excess bismuth is expected to act as point defects and occupy interstitials positions, which in turn interact by oxygen vacancies. These defects are likely to promote defect driven ferromagnetism in BFO system. Incorporation of Gd in presence of excess bismuth in BFO enhanced both spin and electric polarization at room temperature. We also infer that Gd substitution in BFO is likely to suppress spiral spin modulation, which also favors ferromagnetism in Gd-BFO. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on multiferroic properties of Ho substituted BiFeO3 (Bi1−x Ho x FeO3) ceramics. It is observed that for x=0.15, a prominent ferroelectric loop is seen at 300K even if the system remains in rhombohedral (R3c) phase without appearance of any observable impurity phases. A well shaped M–H loop is observed at 10K for x=0.15. However it showed ferromagnetism, confirming the contribution of Ho3+ towards enhancement of ferromagnetic properties of BiFeO3 at 300K. Suppression of impurity phases of pure BiFeO3 bulk ceramic favors the reduction of mobile oxygen vacancies and reduces leakage current, due to which ferroelectric properties of BiFeO3 is enhanced. We argue that Ho substitution at Bi site is likely to suppress the spiral spin modulation and at the same time increase the canting angle, which favors enhanced multiferroic properties. XRD, SEM, magnetization, polarization and chemical bonding analysis measurements were carried out to explain the multiferroic behavior. [ABSTRACT FROM AUTHOR]

Abstract: Room temperature ferromagnetism (RTFM) with a saturation magnetization (M s) of 0.025emu/cm3 has been observed in single crystal of zinc oxide (ZnO). The presence of intrinsic defects like zinc (Zn) interstitials and oxygen (O) vacancies in single crystal ZnO is established through micro-Raman and photoluminescence studies. The role of intrinsic defects in introduction of RTFM in single crystal ZnO is discussed. [Copyright &y& Elsevier]

Abstract: We observed that ZnO bulk ceramics prepared by solid state reaction route at 1300°C exhibited unexpected room temperature ferromagnetic (RTFM) property. In the absence of any magnetic impurity the cause of room temperature ferromagnetic signal in the undoped system is certainly attributed to various kinds of native defects such as oxygen vacancies (V O) or zinc interstitials (I Zn) and their clusters created inside the bulk ceramics during heating by slow step sintering schedule (SSSS). The micro-Raman investigation and X-ray photoelectron spectroscopy studies on the ZnO sample sintered at high temperature confirm the presence of such lattice defects. [Copyright &y& Elsevier]

Abstract: Europium-doped cubic barium titanate (BT) nanocrystals with % [Eu/Ti] mol ratio varying from 0.05 to 0.25 were prepared through hydrothermal route. The nano nature of these powders was confirmed by XRD and TEM studies. Pellets were prepared after calcining the powders at 1000 °C for 2 h. These pellets were annealed at 200, 500, 700 and 1000 °C for 2 h at each temperature and used for dielectric measurements. Raman spectra of two typical pellets with %[Eu/Ti] Eu/Ti mol ratios of 0.15 and 0.25 showed all the peaks characteristic of tetragonal BaTiO3. Pure BT showed a low dielectric constant (DC) with a value of 398. Doping with small amounts of Eu resulted in many fold increase of DC values. A maximum value of 10576 at 1 KHz frequency was observed for the sample with % [Eu/Ti] mol ratio of 0.15. Lowering of Curie temperature T c (95 to 110 °C) was observed for pure as well as Eu-doped barium titanate. [Copyright &y& Elsevier]

Abstract: This paper reports a novel and low-cost thermal plasma assisted heating method for ultrafast sintering of rare-earth-based perovskite manganites. An indigenously designed DC thermal plasma reactor has been used to sinter La0.67Ca0.33MnO3 (LCMO) colossal magnetoresistance (CMR) material. Highly dense (96% of theoretical density) crystalline bulk LCMO ceramics were prepared within 2.5min of sintering time. Plasma-sintered LCMO bulk ceramics showed enhanced T C (272K), which is close to T IM (275K) as compared to the conventional sintered LCMO [J.M. De Teresa, M.R. Ibarra, J. Blasco, J. Garcia, C. Marquina, P.A. Algarabel, Z. Arnold, K. Kamenev, C. Ritter, R. von Helmolt, Phys. Rev. B 54 (1996) 1187] sample. We observe that the thermal plasma heating process offers a unique advantage for quick physical densification and hence sintering within a few minutes. [Copyright &y& Elsevier]

Abstract: MgO-doped Al–Zr oxide composites of Zr0.95Al1.05Mg x O with x =0, 0.01,…,0.05, 0.75, 1 were sintered to high density by both dc thermal plasma assisted rapid sintering as well as conventional sintering. It was observed that the above mentioned MgO-doped Al–Zr oxide composites were sintered to high density end products by the thermal plasma heating technique within a short sintering time (a few minutes) as compared to a conventional long range resistive heating schedule (a few tens of hours). Moreover, the densities of plasma sintered samples were found to be more than that of conventional sintered samples. It was also noticed that there exists a critical limiting point of MgO doping concentration (x =0.05 in Zr0.95Al1.05Mg x O) for maximum physical densification in both conventional as well as plasma sintered samples. Sintered specimens were analyzed by XPS, XRD and EPMA studies. XRD, XPS and EPMA studies revealed the presence of a high density phase, Mg2Zr5O12 prominently in x =0.05 sintered sample which resulted in maximum densification of the sample. Thus, MgO doping in small amounts promotes physical densification. [Copyright &y& Elsevier]

Abstract: A series of systematic substitution of isovalent Sr ion into the Ca site of system has been studied for different values ranging from . It is observed that at , the system begins to exhibit multiphasic behavior with the onset of X-ray shoulder peak at value of . In this paper, we report low field SQUID magnetization behavior and electrotransport properties of the above system with , 0.033 and 0.066. It is noted that larger cationic size () does not allow the system to attain low bandwidth, which is the important parameter to control the electric and magnetic properties including Curie temperature and metal insulator transition temperature . The role of ion substitution as larger radius with respect to ion in the system can specifically be assigned to enhance the electron bandwidth (), which promotes higher and . In addition to this, an interesting spin glass cluster and transition phenomena are observed at low temperature region for . [Copyright &y& Elsevier]

Abstract: The effect of annealing on the properties of La0.7Sr0.3MnO3 (LSMO) thin film deposited on Si substrates by DC sputtering has been investigated by X-ray diffraction (XRD), electrical and magnetic measurements. As-grown films show a lower metal–insulator transition (T MI) temperature than annealed films. As the annealing temperature increases, significantly higher T MI values are observed up to 270K. We suggest that the increase of effective hole doping, induced by cationic vacancies due to the excess oxygen, is a possible reason for the observed trend in T MI. Annealing improves the magnetic homogeneity of the grain and grain boundaries. These improvements are favorable to enhance the intrinsic properties of the compound especially the decrease of resistivity. The decrease in resistivity induces the MR ratio to increase. This result is attractive for CMR application studies. [Copyright &y& Elsevier]

Abstract: La0.67Ca0.33MnO3 (LCMO) thin films were successfully fabricated by a DC magnetron sputtering technique on Si (100) substrates from chemically synthesized compacted powders. Powders of proper stochiometry composites were synthesized by a novel chemical technique [D.R. Sahu, B.K. Roul, P. Pramanik, J.L. Huang, Physica B 369 (2005) 209] and were found to be nanosized (≈40–50nm). The sinterability of the powders were improved significantly due to their large surface area with a reduction of sintering temperature (up to 500°C) as compared to the powders prepared by other solid-state reaction route. Bulk LCMO targets were prepared and preliminary structural and magnetic properties of target were investigated for colossal magnetoresistance (CMR) properties. Films deposition parameters like DC power, gas flow rate, deposition time, etc., were critically optimized to achieve desired thickness of film using above LCMO target by DC magnetron sputtering. LCMO films fabricated on Si (100) substrates showed enhanced magnetoresistance (MR) at low temperature. Maximum MR of about 1000% was observed at 100K. Paramagnetic to ferromagnetic transitions were observed in films below room temperature and were found at approximately 240K. However, as compared to bulk target prepared by a chemical route, it was found that Curie temperature (T c) and MR response of bulk target were higher than the thin films. Preliminary point chemical analysis revealed the deficiency of Ca2+ ions in CMR films. [Copyright &y& Elsevier]

Abstract: Sintering behaviour of sequentially varied metal ion concentration in Al x –Zr100−x (x =0, 10, 20, …, 100) based oxide composites were studied using conventional solid state sintering process in the temperature range 1400–1600°C. Critical experimental parameters like green density, sintering time and temperature were varied to achieve higher sintered product. Systematic studies of densification, structural, microstructural, hardness and shrinkage properties were carried out to understand the real sintering process development mechanism involved in this oxide matrix during initial, intermediate and final stage of sintering. Interesting development in connection with microstructural and phase evolution, pore-grain network in relation to physical densification and hardness behaviour are analysed and it is noted that compositional variation in Al x –Zr100−x oxide matrix (x =0, 10, 20, …, 100) produces structural (monoclinic to tetragonal) phase separation (complete or partial) at different sintering temperatures (1400–1600°C). Long heating schedule (20h) at high sintering temperature (1600°C) promotes highest percentage of monoclinic–tetragonal transformation at x =30 in Al x –Zr100−x oxide composites. [Copyright &y& Elsevier]

A simple and low cost heating technique based on extended arc thermal plasma heating (EATPH) source has been developed to sinter high temperature Alx–Zr100−x (x=0, 10, 20, …, 100) oxides. Structure and morphology of sintered Al–Zr oxide samples were studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). Interesting result pertaining to the reduction of dielectric constant (K) and dielectric loss (tan δ) were noted in thermal plasma sintered specimen as compared to the conventional sintered sample using resistive heating. It is observed that values of K are reduced up to 40% (maximum) w.r.t. conventional sintering. This low K behavior observed in thermal plasma sintered sample may be attributed to the incorporation of dynamic inclusion in different defect form during thermal plasma heating within a short sintering time. It is also further observed from the frequency and temperature variation of K and tan δ that surface charge polarization along with dipole screening play an important role at high frequencies and temperatures which can be explained by dipole pinning and depinning mechanisms. [Copyright &y& Elsevier]

A series of highly dense Ho-doped La0.67Ca0.33MnO3 (LCMO) bulk ceramic samples were processed in the temperature range 1450 to 1600 °C and performed transport measurement (temperature down to 5 K and magnetic field up to 7 T). The effect of sintering time and temperature on transport properties are reported here. The magnetization and resistance decreased as sintering temperature is increased. Surface structure and morphology were studied by XRD, SEM and TEM. XRD pattern showed the monophasic orthorhombic structure of the sample sintered within the above temperature range for a sintering period of 20 h. It is surprising and interesting to observe that at certain critical doping level transition temperature is increased significantly indicating its potential use in CMR-based device technology above room temperature. In this paper, we report that critical optimization of sintering parameter is very important to achieve enhanced transport and magnetic properties. [Copyright &y& Elsevier]

We have performed magnetic and transport measurements on La[sub 0.67]Ca[sub 0.33]MnO[sub 3] polycrystalline and partially melted samples. The magnetization and resistance decrease as sintering temperature is increased. The insulator-to-metal transition temperature is remarkably enhanced in the partially melted sample, enabling its possible applications at room temperature. The microscopic studies in melt samples show an excellent connectivity between grains, suggesting the enhancement of percolative transport by opening new conduction channels and the disappearance of magnetic phase boundary at elevated temperature by the ordering of Mn spins blocked at the grain boundary of sintered samples. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]