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Magnetic hysteresis loops are measured on Bi2Sr2CaCu2O8+δ (Bi-2212) single crystal with different surface states and shapes. The result obtained on Bi-2212 single crystals with dirty and clean surfaces demonstrates that variation of surface state does not result in the disappearance of anomalous magnetization peak H2p and has only an influence on the width of magnetic hysteresis loops. The result obtained on Bi-2212 single crystals with elongated and circular shapes shows that the variation of shape also does not give rise to the disappearance of H2p. The origin of H2p of Bi-2212 single crystal is suggested to originate from other intrinsic reasons and should not be attributed to the surface state and surface shape. [Copyright &y& Elsevier]

Flux pinning and anomalous magnetization peak of heavily overdoped Bi[sub 2-x]Pb[sub x]Sr[sub 2]CaCu[sub 2-y]Cr[sub y]O[sub 8+δ] [Cr-doping (Bi, Pb)-2212] single crystals are investigated by means of magnetization measurements with the magnetic field parallel to the c axis. Compared with undoped Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+δ] (Bi-2212) and Pb-doping Bi[sub 2-x]Pb[sub x]Sr[sub 2]CaCu[sub 2]O[sub 8+δ] [(Bi, Pb)-2212] single crystals, the irreversibility line of Cr-doping (Bi, Pb)-2212 single crystals is pronouncedly shifted to high temperatures. The anomalous magnetization peak H[sub 2p] with maximum peak field near 8000 G is observed. The H[sub 2p] exhibits strong temperature dependence from 0.19 to 0.93T[sub c]. The temperature dependence of H[sub 2p] can be explained according to vortex decoupling theory. The improved flux pinning may originate from reduced anisotropy due to Pb doping and a sufficient number of effective pinning centers due to the random Cr substitution on the Cu site. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Bi2−xPbxSr2CaCu2Oy ((Bi,Pb)-2212) single crystals with a large doping range up to x=0.8 have been grown by the conventional self-flux method. The resistivity anisotropy of (Bi,Pb)-2212 single crystals and their transport properties under applied magnetic fields with H∥c have been systematically studied. In-plane resistivity (ρab), out-plane resistivity (ρc) and anisotropy (γ) of (Bi,Pb)-2212 are significantly reduced by heavy Pb doping. The dissipation behavior of (Bi,Pb)-2212 single crystals in the mixed state can be well described by the thermally activated flux creep model and flux creep is obviously suppressed for heavily Pb-doped single crystals. The origin of the improved flux pinning is suggested to stem mainly from the reduced anisotropy and the improved coupling strength between Cu–O layers due to Pb-doping. [Copyright &y& Elsevier]

MgB2/Cu tapes were fabricated by power-in-tube technique using MgB2 superconducting powder and no post-annealing treatment was performed for the prepared tapes. Both X-ray diffraction and scanning electron microscopy results indicate that there is no obvious texture of grains for the tape samples. However, compared with the bulk sample, evident shifting and broadening of diffraction peaks is observed and Tc is reduced for the tape samples. In addition, it is found that there exists a remarkable difference in flux pinning ability for tapes prepared using wires with different diameters. The difference seems to originate from the different strain and microstructure defects of MgB2 grains caused by cold working. [Copyright &y& Elsevier]

Anomalous magnetization is investigated on a heavily Pb-doped Bi2Sr2CaCu2O8+δ as-grown single crystal [(Bi,Pb)-2212] with Tc=92 K. Both the anomalous magnetization peak H2p and the onset of the anomalous magnetization peak Hon are detected in temperature region from 0.3Tc to 0.9Tc based on the descending field branch of magnetic hysteresis loops. At low temperatures below 20 K, the magnetic hysteresis loop behaves as an obvious asymmetry. The double magnetic hysteresis behavior is observed at high temperatures close to Tc. The temperature dependence of H2p can be described according to the thermal disorder induced decoupling theory. The double magnetization behavior may be ascribed to the existence of intra-grain granularity due to the inhomogeneity of oxygen distribution induced by heavily Pb-doping. [Copyright &y& Elsevier]

Abstract: Nanosized La0.8Sr0.2MnO3 (LSMO) are prepared by the sol–gel method. The ceramic composites (LSMO) x /(ZrO2)1−x are obtained using solid-state sintering. The magnetoresistance (MR) of composites is explored as a function of the manganite/insulator composition, temperature, and magnetic field. Enhancements of the low-field magnetoresistance (LFMR) are observed in the composites. For instance the MR ratios at 150 K with H =300 Oe are 0.7% and 8% for the x =0.8 and 0.25 samples, which are 4.5 times and 53 times as large as that for pure LSMO, respectively. The improved field sensitivity (dMR/dH) has a maximum at x =0.25, around which the system exhibits a conduction percolation threshold. The spin-dependent tunneling and scattering at the interfaces of grain boundaries are responsible for the enhanced LFMR. [Copyright &y& Elsevier]

Abstract: Systematic studies of X-ray, magnetic, electronic transport, and elastic properties have been performed on polycrystalline Bi0.5Ca0.4Sr0.1MnO3 sample. The sample exhibits charge ordering (CO) state below T CO (=304K), accompanied by a distinct maximum in magnetization. The softening of Young''s modulus in the vicinity of T CO indicates that there is a strong coupling of electron–phonon due to Jahn–Teller (JT) effect. The dynamic ferromagnetic spin correlations are observed at high temperatures above T CO, which are replaced by antiferromagnetic (AFM) spin fluctuations at a concomitant CO transition. Below 32K, a spin-glass (SG) state dominates at low temperatures. The voltage–current (V–I) characteristics measurement results indicate that the non-linear conduction starts above a threshold current, giving rise to a region of negative differential resistance (NDR). The origin of the non-linear conduction is discussed in view of current induced collapse of CO state associated with phase-separation mechanism. [Copyright &y& Elsevier]

Abstract: The structural study of Sr0.9Ce0.1Mn1–y Cr y O3 (, 0.05, and 0.10) has been carried out by X-ray diffraction. For undoped sample Sr0.9Ce0.1MnO3, it undergoes a first-order structural transition accompanied by Jahn–Teller (JT) transition at . The JT transition temperature is reduced in Cr-doped samples, becoming for . The tetragonal structure is characterized by the JT distortion in MnO6 octahedra with the distortion mode . With increasing Cr doping content, the deformation of MnO6 octahedra is weakened, showing that Cr doping destabilizes the JT effect. In addition, elastic properties measurement indicates that a large softening of Young''s modulus occurs in the vicinity of , which has been interpreted in terms of the strong electron–phonon coupling originating from the JT effect. [Copyright &y& Elsevier]

Abstract: Cr-doped manganites Sr0.9Ce0.1Mn1−y Cr y O3 (y=0, 0.05, and 0.10) have been systematically investigated by X-ray, magnetic, transport, and elastic properties measurements. For parent compound Sr0.9Ce0.1MnO3, it undergoes a metal–insulator (M–I) transition at 318K, which is suggested to originate from a first-order structural transition accompanied by Jahn–Teller (JT) transition. With increasing Cr doping content, the JT transition temperature decreases. The Cr doping suppresses the antiferromagnetic (AFM) state and makes the system spin-glass (SG) behavior at low temperatures. In the vicinity of JT transition temperatures, the softening of Young''s modulus originating from the coupling of the orbital (quadrupolar) moment of the eg orbital of Mn3+ ion to the elastic strain has been observed. The anomalous Young''s modulus properties imply the electron–phonon coupling due to the JT effect may play an important role in the system. [Copyright &y& Elsevier]

Abstract: Electron-doped manganite Sr0.8Ce0.2MnO3 has been systematically investigated by X-ray diffraction, electronic transport, magnetic, internal friction, and Young''s modulus experiments. The X-ray diffraction result indicates that the compound remains tetragonal (I4/mcm) structure at room temperature. Due to the strong Jahn–Teller (JT) distortion, the ground state is antiferromagnetic (AFM) insulator. Below 20 K, a spin-glass (SG) state dominates at low temperatures. In the paramagnetic (PM) region, an internal friction peak at around 250 K, which is characteristic of relaxation, has been observed. Under applied magnetic field, the internal friction peak moves to higher temperature, which is suggested to originate from the formation of ferromagnetic (FM) clusters in PM region. In addition, the softening of Young''s modulus in the vicinity of AFM transition temperature is interpreted in terms of the strong electron–phonon interaction. [Copyright &y& Elsevier]

Abstract: The role of vibrational anisotropy of Mn3+O6 octahedron in the phase separation behavior of La0.67−y Pr y Ca0.33MnO3 (x=0, 0.15, 0.25 and 0.30) has been investigated by means of magnetization M, internal friction Q −1, Young''s modulus E along with the X-ray powder diffraction measurements. For the samples with y=0 and 0.15, the Q −1 exhibits three peaks in the ferromagnetic region, which are attributed to the intrinsic inhomogeneity of ferromagnetic phase, i.e. the electronic phase separation with the coexistence of insulating and conducting phases. However, both the samples with y=0.25 and 0.30 undergo a magnetic phase separation with the coexistence of the antiferromagnetic and ferromagnetic phases, and the Q −1 peaks related to the electronic phase separation have not been observed. In addition, the Q −1 exhibits a peak in the paramagnetic region for all samples, which may result from the formation of magnetic clusters. We observed that the evolution from electronic to magnetic phase separation is close related to the rapid increase in the ratio of two kinds of Jahn–Teller distortion modes Q 3 and Q 2, i.e. Q 3/Q 2. A schematic phase diagram is given in the text, and it is suggested that the enhancement of vibrational anisotropy of Mn3+O6 octahedron plays a key role in the evolution from electronic to magnetic phase separation. [Copyright &y& Elsevier]

Abstract: We have investigated the influence of electric current on the charge-order (CO) state in La0.25Ca0.75MnO3 manganite by means of in-situ measurements of the temperature dependence of Young’s modulus and resistivity . We also measured simultaneously some magnetic properties. exhibits a minimum that may be due to the competition between short-range ferromagnetic (FM) and short-range aniferromagnetic (AFM) order in the temperature region between AFM transition and the charge ordering transition temperature . Both and are obviously lowered with increasing current at low temperatures. The correlation of these changes in and is discussed and the resistivity drops induced by the current is suggested to originate from the lattice variation. [Copyright &y& Elsevier]

The effect of Ho-doping and Ho-adding on the electronic transport and magnetic properties of melt-processed La0.67Ca0.33MnO3 (LCMO) is investigated by resistivity and AC susceptibility measurement. For Ho-addition of 1 mol% LCMO sample (Ho-LCM), its magnetic transition temperature Tc and metal–insulator (M–I) transition temperature Tp are enhanced about 70 K compared with Ho-free LCMO sample. However, for Ho-doping of 3 mol% LCMO sample (Ho-doping LCM), both Tc and Tp are reduced about 35 K. We give a reasonable explanation in terms of structural changes (bond distance and bond angle) gained from the XRD refinement. The nanoscale Ho distribution is consistent with the magnetic inhomogeneity induced MR which is verified by the double peaks in AC susceptibility χ″ and the drop of χ′(T) curve below Tc. The mechanism of transport of all the samples is discussed. [Copyright &y& Elsevier]

The resistive transitions of (Bi, Pb)2Sr2Ca2-xPrxCu3Oy silver sheathed tapes with x=0.0, 0.001, 0.002 have been measured under applied magnetic fields oriented perpendicular to tape plane (Hǁc) from 0 to 7 T. The transitions can be well agreed with the thermally activated flux creep model by Anderson: R(T,H)=R0exp[-U(H)/kBT] in the low resistance range. Under lower applied magnetic field the calculated activation energies U(H) of flux motion increased drastically in the samples with proper amount of Pr-ion defects, for example, U is about 29,000 K for tape with x=0.001 at 0.025 T while that is 4200 K for that without ion defects. For our samples, U are all well fitted with the law of U/(1-Tirr/Tc0)∝1/Hα. With the doped Pr-ion defects, the data α are obviously increased from 0.67 to 1–1.22. The markedly changed α indicated the flux creep according to varied manners in different samples. [Copyright &y& Elsevier]

The author of the comment is too unilateral to associate double-peak behaviour (broad insulator–metal (I–M) transition below the Curie temperature (Tc)) and a sharp one near (Tc) in rare-earth manganese perovskites only with the grain boundaries (GB) effect. Moreover, it is especially confused that the grain-size effect should be necessary to relate with this electronic transport behaviour. In this reply, we provide an argument in support of the statement that inhomogeneous electronic/magnetic phase separation is one of the most important reasons for the double-peak behaviour in the ρ(T) curve. [Copyright &y& Elsevier]