桑原 英樹

Magnetic circular dichroism in the soft-X-ray absorption spectra in the Mn 2p -> 3d excitation region has been measured for Nd1-xSrxMnO3 (x = 0.40, 0.47, 0.50). Small but clear differences in XAS and MCD spectra are found with respect to x compositions. We will discuss the total moment estimated from both XAS-MCD spectra and magnetization measurement. (c) 2005 Elsevier B.V. All rights reserved.

We have investigated dielectric properties in Mott insulators GdMnO3 and TbMnO3 under magnetic fields and external quasihydrostatic pressures. In the case of GdMnO3, thermal hysteresis for dielectric constant s and discontinuous lattice distortion were observed at ferroelectric transition temperature (T-C), and ferroelectric spontaneous polarization was suppressed by the application of external pressure. These results indicate that the ferroelectric transition in GdMnO3 is a first-order displacive-type one. On the other hand, the thermal hysteresis and discontinuous lattice striction were not observed at T-C in TbMnO3. The peak of E corresponding to the ferroelectric transition was shifted toward higher temperatures by the application of external pressure in TbMnO3. The ferroelectric transition of TbMnO3 was thought to be a second-order order-disorder-type one. (c) 2005 American Institute of Physics.

We have investigated dielectric properties in a series of crystals of RMnO3 (R is a rare-earth ion) under magnetic fields and quasihydrostatic pressure. We have found that a ferroelectric phase appeared in GdMnO3 crystal below 13 K. We have confirmed that a small spontaneous polarization exists along a-axis (P-a) in the orthorhombic Pbnm setting and that P-a can be reversed by the DC electric field. The dielectric anomaly due to the ferroelectric transition accompanied thermal hysteresis and lattice striction. The ferroelectric transition temperature decreased with quasi hydrostatic pressure. These results indicate that the ferroelectric transition is improper and is of the first-order displacement type. P-a was easily collapsed by the application of a magnetic field of 0.4 T parallel to the spin-canting direction (H parallel to c) while it was enhanced parallel to the easy axis (H parallel to b). (c) 2005 Elsevier B.V. All rights reserved.

Photoinduced effects in a single crystal of bilayered manganites, La2-2xSr1+2xMn2O7 (x = 0.38), were investigated in a wide range of temperatures by pump-probe measurement at a photon energy of 1.6 eV. In a ferromagnetic metallic state, significant enhancement of positive rise in differential reflectivity with a slow relaxing time of 100 ps was observed just below T-C = 127 K, indicating that the reflectivity change with the slow relaxation time constant is induced by laser heating. We have also observed an unconventional fast relaxing component that has a time constant of the order of 10 ps. This fast relaxing component, whose absolute value has an asymmetric peak at T-C, is presumably due to short-range correlation of Jahn-Teller distortion. (C) 2004 Elsevier Ltd. All rights reserved.

We have investigated the carrier-doping x dependence of Seebeck coefficient S(T) and resistivity rho(T) in Nd1-xSrxMnO3 (0.20 <= x <= 0.80) crystals. In the typical ferromagnetic region, S(T) is well explained by the Mott formula. The sign of S(T-C) was found to change from negative to positive near the metal insulator phase boundary. In addition, we have discovered that the power factor, S-2/rho; is optimized at x = 0.63 where the A-type antiferromagnetic metal and the C-type antiferromagnetic insulator coexist. (C) 2003 Elsevier B. V. All rights reserved.

We have studied the effects of the magnetic field up to 10 T on Raman spectra at 40 K in (Nd0.5Sr0.50)MnO3. The folded-phonon modes due to the superlattice in the charge-ordered phase disappear at 10 T, indicating the phase transition to the ferromagnetic metallic phase. We have observed a clear magnetic-field hysteresis. (C) 2003 Elsevier B.V. All rights reserved.

We performed pump-probe transient reflectivity measurements at d-d transition of bilayered perovskite manganite La2-2xSr 1+2xMn2O7 (x=0.38). Signals that suggest coexistence of spin-glass state and ferromagnetic metallic state were observed. © 2003 Optical Society of America.

We have investigated Hall-effect and magnetotransport properties of Nd-based manganite crystals with controlled band filling. We have determined normal (R-H) and anomalous (R-S) Hall coefficients as a function of temperature in the ferromagnetic metallic crystal. The obtained effective carrier number (1/eR(H)) is about 1.0 hole/Mn site, which does not depend on temperature and nominal hole concentration. We have also found magnetoresistance (MR) in the over-doped samples showing various electronic, magnetic, and orbital structures. In C-type antiferromagnetic insulator (0.63less than or equal tox), the rho-T curve below 45 K is well explained by the variable-range hopping (VRH) mechanism. A large negative MR, which is increased with decreasing temperature, was observed in VRH region. The localization length from the characteristic temperature of VRH increases with magnetic field, which indicates that application of magnetic field induces a reduction of energy gap from E-F to the mobility edge by the Zeeman shift. (C) 2003 American Institute of Physics.

We have investigated electronic transport and magnetic properties of Nd1-xSrxMnO3 crystals with controlled band filling (0.5less than or equal toxless than or equal to0.8) grown by the floating zone method. The detailed phase diagram of over-doped Nd1-xSrxMnO3 was obtained through magnetization, resistivity, and crystal structure measurements. We have found the phase boundary from an insulator with tetragonal symmetry to a metal with pseudocubic one at high temperatures approximate to450 K. The observed insulator-metal phase transition is attributed to the orbital order-disorder transition. (C) 2003 Elsevier Science B.V. All rights reserved.

We report the Sr-concentration dependence of Raman spectra in (Nd1-xSrx)MnO3 (x similar to 1/2). In the charge-ordered phase of the x = 0.50 and 0.49 samples, several new Raman peaks appear. In the x = 0.48 sample, no new Raman peak is observed, indicating that the charge-ordered phase transition does not occur. We propose that the symmetry of the lattice in the charge-ordered phase is Pnmm. (C) 2003 Elsevier Science B.V. All rights reserved.

Magnetic domain structures of Nd1/2Sr1/2MnO3 were investigated by means of low-temperature Lorentz electron microscopy. On cooling, magnetic domain walls started to appear at 250 K, and they were oriented straight along the [100] and [110] directions. With a further decrease in temperature, the volume of each magnetic domain increased with discontinuous domain-wall jumps. A characteristic granular image was observed at around 140 K, near the charge-ordering transition temperature. We consider that this originated from ferromagnetic nanoclusters that appeared in the antiferromagnetic matrix.

Optical three-photon difference frequency generation (DFG) was observed in Pr1-xCaxMnO3 (x=0.30, 0.40) and Nd1-xSrxMnO3 (x=0.48, 0.50). In the paramagnetic phase, the DFG signal reflects the fourfold anisotropy of the quasicubic crystal, and all the independent tensor elements for DFG near 2.0 eV are determined. Below T(N)approximate to150 K, a two-order-parameter coupling to both antiferromagnetism and charge ordering leads to additional DFG contributions which allow to observe the formation of similar to100 mum large magnetic domains. (C) 2002 American Institute of Physics.

We have measured the temperature dependence of Raman spectra in (Nd0.5Sr0.5)MnO3. New phonon modes are observed in the charge-ordered phase. A change of the lattice symmetry at the charge-order phase transition and extraordinary behavior of the low-frequency Raman spectra are reported. (C) 2002 Elsevier Science B.V. All rights reserved.

Magnetization and magnetoresistance. were measured in A-type antiferromagnet Nd0.45Sr0.55MnO3 utilizing pulsed magnetic fields up to 45 T. We have observed a ferromagnetic transition accompanied by a discontinuous decrease of resistivity. The temperature dependence of the resistivity in the ferromagnetic state showed characteristics of a three-dimensional metal. The observed phenomena are explained in terms of simultaneous destruction of the d(x2-y2) orbital ordering and the A-type anti ferromagnetic spin ordering by magnetic field.

We have studied the phenomena relevant to charge/orbital ordering in perovskite manganites. In the three bandwidth controlled systems, La-0.7(Sr1-yCay)(0.3)MnO3 (x=0.3), (Nd1-ySmy)(0.55)Sr0.45MnO3 (x=0.45), and Pr-0.65(Sr1-yCay)(0.35)MnO3 (x=0.35), the variation of the magnetic and electronic properties with y has been studied as the hole doping level is kept constant. As y increases (the effective one-electron bandwidth decreases), the colossal magnetoresistance (CMR) or charge /orbital ordering appears. That is, the CMR is caused by competition between double exchange and charge/orbital ordering. As another issue, the electronic and magnetic properties of the ordered double perovskite Sr2FeMoO6 (T(C)similar to 420 K) have been studied by utilizing single crystals. (C) 2001 Elsevier Science BY. All rights reserved.

Pr(1-x)Ca(x)MnO(3) and Nd(1-x)Sr(x)MnO(3) were investigated with three-photon difference frequency generation (DFG). This method allows one to determine both the crystalline and the magnetic symmetry. In the highly ordered low-temperature phase of Nd(0.50)Sr(0.50)MnO(3), a DFG contribution coupling simultaneously to antiferromagnetic and charge ordering was observed and used to reveal the formation of domains. Thus, magnetically induced three-photon processes are introduced into the fields of both nonlinear magnetooptics and colossal magnetoresistance as a powerful new method.

Spin wave excitations were measured in the ferromagnetic phase of Nd1/2Sr1/2MnO3 by neutron scattering. This compound is located in proximity to the A-type antiferromagnetic state, and it shows a clear anisotropy and anomalous softening of the spin wave excitations. The softening in the ferromagnetic phase is induced by the orbital ordering. (C) 2001 Elsevier Science B.V. All rights reserved.

Magnetization and magnetoresistance of Nd0.45Sr0.55MnO3 have been measured in pulsed magnetic fields up to 45 T. Application of high magnetic field causes metamagnetic transitions below the Neel temperature T-N similar to 220 K. Temperature dependence of the resistivity under ferromagnetic state after the transition showed characteristics of a three-dimensional metal. The observed ferromagnetic transition and transport properties in the ferromagnetic state can be attributed to the collapse of planar orbital ordering by magnetic field. (C) 2001 Elsevier Science B.V. All rights reserved.

X-ray diffuse scattering measurements on Pr1-xCaxMnO3 and (Nd1-ySmy)(1-x)SrxMnO3 have been performed and characteristic patterns of the intensity distribution were observed. In Pr1-xCaxMnO3 exhibiting the charge-ordering transition, the intensity maxims were observed around (0, +/- zeta, 0) and (+/- zeta, 0, 0) with zeta similar to 0.4 at 300K. The value of zeta increases with decreasing temperature and discontinuously changes to 0.5 at the transition temperature. In (Nd1-ySmy)(1-x)SrxMnO3, the diffuse scattering profiles have intensity maxima around zeta similar to 0.3. The intensity increases with decreasing temperature above the ferromagnetic insulator-metal transition temperature (T-C), but its intensity vanishes below T-C. The local Jahn-Teller distortion associated with an independent polaron can account For the intensity patterns observed in both systems except for the local intensity maxims.

In 3-dimensional peroskite-type manganites RE(1-x)AE(x)MnO(3) (RE:trivalent rare earth ions, AE:divalent alkaline earth ions), the hydrostatic pressure enhances the double exchange (DE) interaction through the increase of the transfer integral, t. In terms of the increase of kinetic energy of carriers, such effect is quite similar to those of other perturbation such as the magnetic field, chemical pressure, carrier doping and so on. In this paper, the various IM transition induced by the hydrostatic pressure are shown and the analogy between the hydrostatic pressure and other external stimulus are discussed. Furthermore, the possibility of the critical state phase control in manganites by using the hydrostatic pressure is presented.

Muon spin relaxation (mu(+)SR) spectroscopy has been applied to study spin dynamics in the manganite single crystal Nd0.5Sr0.5MnO3. Critical slowing down of Mn spin fluctuations has been observed above the ferromagnetic ordering temperature T-C similar to 251 K. The dynamic critical exponent z = 2.00(12), deduced from muon spin relaxation rates above T-C (nonasymptotic regime) agrees with the results of 3d dipolar ferromagnets. Root-exponential relaxation is observed above 160 K and has been attributed to muon spin relaxation in local regions containing differently sized small spin clusters. (C) 2000 Elsevier Science B.V. All rights reserved.

Local magnetic state of Mn atoms in ferromagnetic perovskite-type manganites is investigated with magnetic circular dichroism (MCD) of Mn 2p core-level absorption (XAS). Small but clear differences in XAS and MCD spectra are found between La0.84Sr0.16MnO3 and Nd0.53Sr0.47MnO3. The electronic states of Mn atoms, especially the local spin and orbital states are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

Magnetic ion spin dynamics has been investigated in the perovskite manganite Nd1-xSrxMnO3 single crystals at the hole concentrations x of 0.5 and 0.55 by muon spin relaxation (mu(+)SR) spectroscopy. We have observed the critical slowing down of Mn ion spin fluctuations on approaching the ferromagnetic ordering at similar to 251 K in Nd0.5Sr0.5MnO3. The critical paramagnetic spin fluctuations, measured by the muon spin relaxation rate lambda(1), exhibit a crossover behavior from exchange critical regime to dipolar critical regime. This crossover is explained by considering the suppression of longitudinal and transverse components of spin susceptibility by dipolar interactions closer to T-C and the dipolar vector q(D) is found to be 0.020(2) Angstrom (-1). The dynamic critical exponent z = 2.00(12), deduced from muon spin relaxation rates away from Te (nonasymptotic regime), agrees with the experimental and the theoretical results of 3d dipolar ferromagnets. Critical slowing down is not observed in the x = 0.55 crystal at the onset of antiferromagnetic ordering at similar to 220 K. Muon spin relaxation in the x = 0.5 crystal (above T-N approximate to 5 160 K) and in the x = 0.55 crystal (both above and below TN) is root exponential and indicates nondiffusive relaxation mechanism as is in a magnetic glass. The growth of a glasslike relaxation component concomitant with the magnetic ordering has been observed in both the crystals. We suggest that this glassy component originates from those Mn ions located in local regions containing small and differently sized spin clusters.

Using the epitaxial strain, the magnetic and electronic phases can be controlled for thin films of the manganites, La1-xSrxMnO3, grown on perovskite substrates with various lattice parameters. The strain-induced orbital-ordering (disordering) via coupling with the cooperative Jahn-Teller distortion produces different spin-structures, such as ferromagnetic, layer-type or chain-type antiferromagnetic states, and hence different magnetoelectronic characteristics. The spin-orbital phase diagram for La1-xSrxMnO3 films has been obtained in the plane of strain-field (c/a ratio) vs doping x; which carl be quantitatively reproduced by the density-functional electronic-calculation.

X-ray scattering study on (Nd0.125Sm0.875)(0.52)Sr0.48MnO3 has revealed the existence of diffuse scattering in the paramagnetic phase. Its intensity increases with decreasing temperature, but it vanishes at the ferromagnetic transition temperature. This result indicates that local lattice distortion arises from the localization of electrons on Mn sites (polarons). The intensity distributions are in agreement with calculations based on polarons associated with the Jahn-Teller distortion. Correlation between the distortion fields seems to be related to the formation of charge ordering.

We have peformed neutron diffraction measurements on melt-grown polycrystalline samples of Nd1-xSrxMnO3 (0.49 less than or equal to x less than or equal to 0.75). A systematic transformation of the crystalline and magnetic structures of this system was observed. This can be consistently explained by the change of the character of the Mn e(g) orbitals. When increasing x, the Nd1-xSrxMnO3 system exhibits an evolution from a metallic ferromagnetic state, to a metallic A-type antiferromagnetic (AFM), and then Co an insulating C-type AFM state. The CE-type charge-ordered AFM state was observed only in the vicinity of x = 1/2 and it coexists with the A-type AFM state for x greater than or similar to 1/2, indicating that the energy difference between these two states is very small. We also found that the MnO6 octahedra are apically compressed in the CE-type and A-type AEM states due to the d(3x(2)-r(2))/d(3y(2)-r(2)) or d(x(2)-y(2)) orbital ordering, whereas they are epically elongated by the rod-type d(3z(2)-r(2)) orbital ordering in the C-type AFM state. Finally, a selective broadening of Bragg peaks was observed in the C-type AFM phase and its nc dependence strongly suggests the onset of charge ordering for either x=4/5 or x=3/4. [S0163-1829(99)11737-5].

We discuss unusual behavior discovered in spin dynamics in the nearly half-doped manganite systems. Nd0.45Sr0.55MnO3 is a metallic antiferromagnet, and exhibits very anisotropic spin wave dispersion relations. The ferromagnetic (FM) state of Pr1/2Sr1/2MnO3 and Nd1/2Sr1/2MnO3 also exhibit dear anisotropic dispersion relations. Such anisotropy reflects the underlying d(x(2) - y(2))-type Orbital ordering. We also demonstrate that the high temperature paramagnetic state without charge ordering in doped manganites is characterized by the FM spin fluctuations with an anomalously small energy scale for a wide range of doping concentrations. (C) 1999 Elsevier Science S.A. All rights reserved.

Extensive studies on the colossal magnetoresistive (CMR) manganites have revealed important interplay of charge, spin, orbital, and lattice degrees of freedom not only in CMR characteristics but also in anomalous charge and spin dynamics. Here, we overview our latest experimental investigations of the CMR manganites in light of the important role of the orbital degree of freedom. (C) 1999 Elsevier Science S.A. All rights reserved.

Electronic structures of the charge-ordering manganite Nd1-xSrxMnO3 (x similar to 0.5) have been studied by resonant and high-resolution photoemission. The Mn 2p (Nd 3d) resonant photoemission confirmed the Mn 3d (Nd 4f) states hybridized with the O 2p states. The high-resolution Mn 3p resonance spectra show a clear transition from the metal to the charge-orderod insulator for x = 0.5 upon cooling while a Fermi cutoff is seen for x = 0.47 at all temperatures, suggesting that the transition is induced by a subtle competition between the charge-ordering instability and the double-exchange interaction. Temperature and filling dependence of the spectra implies that the electronic states change not gradually but suddenly at the phase boundary.

X-ray diffraction measurements have been performed on Nd0.5Sr0.5MnO3 single crystals at various temperatures and magnetic fields. The temperature dependences of the lattice parameters show abrupt changes in the slopes at the ferromagnetic transition temperature of 250 K. Discontinuous changes in the lattice parameters occur at the charge-ordering transition temperature of 165 K, below which Mn3+ and Mn4+ ions are spatially ordered. In the ferromagnetic phase, the orthorhombic lattice distortion is reduced with decreasing temperature. This behavior can be attributed to a magnetoelastic interaction in this compound. Superlattice reflections corresponding to a doubling of the unit cell along the b axis appear in the charge-ordered phase, and their intensities change very little with temperature and magnetic field except near the transition. When the charge-ordered phase is transformed into the ferromagnetic phase by an external magnetic field, the superlattice reflections vanish and the lattice parameters discontinuously change. Values of the magnetic fields at which the transition occurs are independent of directions of applied magnetic fields.

Below the Neel temperature (T-N) a layered antiferromagnetic (AF) Nd0.45Sr0.55MnO3 crystal is metallic within the ferromagnetic (F) layers (ab plane), while insulating along the AF-coupling direction (c axis), showing an extremely large anisotropy in resistivity. The observed two dimensionality of charge dynamics is due to confinement of the spin-polarized carriers within the F sheets induced by the magnetic ordering as well as orbital ordering (perhaps of d(x2-y2) type). Large negative magnetoresistance is observed over a wide temperature region below T-N, which arises from the dimensional crossover due to the field-induced spin canting in the AF state. [S0031-9007(99)09183-8].

The spin dynamics of Nd0.6Sr0.4MnO3 have been determined along [qqq], [qq0], and [00q] propagation directions using inelastic neutron scattering. At T = 13 K, the low-q Mn-Mn mode energies varied quadratically with wave vector q, but exhibited marked softening on approach to the zone boundaries when compared with a Heisenberg nearest-neighbor exchange calculation. At the larger q's the modes also show evidence of increasing spin wave energy width. The temperature dependence of the spin wave stiffness parameter D was measured up to T-c = 273 K and showed conventional behavior. The 0 K value of D = 150 meV Angstrom(2) yields D(0)/kT(c) = 6.3. No anomalous E = 0 central mode intensity was observed on approach to T-c. At low T additional modes were observed and are ascribed to Nd-Mn exchange interactions. These modes have q = 0 spin wave gap of 2.1 meV compared to 1.1 meV for the Mn-Mn excitations. (C) 1999 American Institute of Physics. [S0021-8979(99)20308-8].

A (Formula presented) NMR study was carried out on melt-grown samples of (Formula presented) (Formula presented) The microscopic magnetic structure of the parent (Formula presented) was identified as a homogeneous antiferromagnet at low temperatures. Substituted compounds with (Formula presented) demonstrate the homogeneous ferromagnetic phase. Only a lightly doped sample with (Formula presented) shows the coexistence of NMR lines from ferromagnetic and antiferromagnetic phases. © 1999 The American Physical Society.

We have peformed neutron diffraction measurements on melt-grown polycrystalline samples of Nd1-xSrxMnO3(0.49 &lt x &lt 0.75). A systematic transformation of the crystalline and magnetic structures of this system was observed. This can be consistently explained by the change of the character of the Mn egorbitals. When increasing X, the Nd1-xSrxMnO3system exhibits an evolution from a metallic ferromagnetic state, to a metallic A-type antiferromagnetic (AFM), and then to an insulating C-type AFM state. The CE-type charge-ordered AFM state was observed only in the vicinity of x = 1/2 and it coexists with the A-type AFM state for x ≳ 1/2, indicating that the energy difference between these two states is very small. We also found that the MnO6octahedra are apically compressed in the CE-type and A-type AFM states due to the d(3x2-r2)/d(3y2-r2) or d(x2-y2) orbital ordering, whereas they are apically elongated by the rod-type d(3z2-r2) orbital ordering in the C-type AFM state. Finally, a selective broadening of Bragg peaks was observed in the C-type AFM phase and its x dependence strongly suggests the onset of charge ordering for either x=4/5 or x=3/4. © 1999 The American Physical Society.

A La-139 NMR study was carried out on melt-grown samples of La1-xSrxMnO3 (0 less than or equal to x less than or equal to 0.15). The microscopic magnetic structure of the parent LaMnO3 was identified as a homogeneous antiferromagnet at low temperatures. Substituted compounds with x greater than or equal to 0.1 demonstrate the homogeneous ferromagnetic phase. Only a lightly doped sample with x = 0.05 shows the coexistence of NMR lines from ferromagnetic and antiferromagnetic phases. [S0163-1829(99)15901-0].

We have investigated the ferromagnetic spin fluctuations in Nd 1/2 Sr 1/2 MnO3, which shows relatively weak colossal magnetoresistance (CMR) behavior at TC. An intense quasielastic fluctuation, a so-called central peak, develops at around the ferromagnetic transition temperature. By comparing the results with those observed in other CMR manganites, we examine which feature of the central component is essential to the CMR phenomenon.

We demonstrate that Nd0.45Sr0.55MnO3 is an example of a metallic antiferromagnetic manganite, and that it exhibits very anisotropic spin-wave dispersion relations with intra- and interplanar exchange parameters 8JS = 32.6 +/- 0.9 meV and 4J' S= - 10.1 +/- 0.5 meV, respectively. This anisotropy reflects underlying d(x)2(-y)2-type orbital ordering, and the metallic behavior indicates that a charge ordering is decoupled from the orbital ordering in this system. [S0163-1829(98)51926-1].

In the case of La1-xSrxMnO3, the ferromagnetic and metallic states have been understood in terms of the double exchange model, while in the compounds with relatively narrow one-electron bandwidth, such as Nd1-xSrxMnO3 or Pr1-xCaxMnO3, the double exchange is weakened and the charge-ordered (Mn3+/Mn4+ ordered) state emerges at x similar to 1/2. In the charge-ordered state, the e(g)-orbitals also order simultaneously and the antiferromagnetic non metallic state is realized at low temperatures. Recent investigations, however, have shown that the antiferromagnetic charge-ordered state can be altered to the ferromagnetic metallic state by applying an external magnetic field. The competition between the double exchange and the charge/orbital-ordering instability plays an important role in the observed field-induced transition, and also in other versatile field-induced phenomena in the perovskite-type manganese oxides. The robustness of charge ordering which depends on both of the (R, A) cations and the carrier concentration is a key factor for those unconventional features. (C) 1998 Elsevier Science B.V. All rights reserved.

We have investigated electronic transport and magnetic properties of perovskite-type Nd1-xSrxMnO3 crystals with change of controlled hole-doping level (0.30 less than or equal to x less than or equal to 0.80). The electronic phase diagram of Nd1-xSrxMnO3 was obtained by systematic measurements of magnetization (magnetic structure), resistivity, and lattice parameter. We have also studied the anisotropic transport properties of x=0.50 and 0.55 crystals with different magnetic structures: CE-type antiferromagnetic (AF) structure for x=0.50 and A-type layered AF one for x=0.55. In the case of the x=0.55 crystal, the metallic behavior was observed within the ferromagnetic (F) layers, while along the AF-coupling direction the crystal remains insulating over the whole temperature region. The observed large anisotropy is due to the magnetic as well as orbital-ordering induced confinement of the spin-polarized carriers within the F sheets. The nearly isotropic transport behavior has been confirmed for the CE-type AF charge-ordered state in the x=0.50 crystal.

Anisotropic charge transport and magnetic properties have been investigated for single crystals of the layered manganite, La2-2xSr1+2xMn2O7 (0.3 less than or equal to x less than or equal to 0.5). Remarkable variations in the magnetic structure as well as in the charge-transport properties are observed with changing doping-level x. A crystal with x=0.3 behaves like a 2-dimensional ferromagnetic metal in the temperature region between similar to 90 K and similar to 270 K, and shows the interplane tunneling magnetoresistance at lower temperatures. These characteristic charge-transport properties are attributed to the interplane magnetic coupling between the adjacent MnO2 bilayers, and are strongly affected by the application of pressure as well as low magnetic fields through the change in magnetic structure. With increase of the carrier concentration toward x=0.5, the charge-ordered phase is stabilized and dominates the charge transport and magnetic properties.