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In ${\mathrm{BaV}}_{10}{\mathrm{O}}_{15}$ with quasitriangular V lattices, we found unique superstructures characterized by $(qq0)$-type peaks in the momentum space, where $q$ varies continuously with temperature between $q=0$ and $1/3$ and locks at $1/3$. Such a threefold superstructure is likely caused by the dense arrangement of the V trimers associated with the orbital ordering of V. The results indicate that the superstructure of the V trimers, each of which is also a superstructure, gives rise to the ordered phases with peculiar characteristics.

We investigated the structural, magnetic, transport, and high-temperature thermoelectric properties of single crystals of the pseudobrookite ${\mathrm{Al}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{2+x}{\mathrm{O}}_{5}$ for $0\ensuremath{\le}x\ensuremath{\le}1$ grown using a floating zone. We found a correlation of spin-singlet ${\mathrm{Ti}}^{3+}\text{\ensuremath{-}}{\mathrm{Ti}}^{3+}$ dimers coupled with the lattice even in the conductive $\ensuremath{\alpha}$ and $\ensuremath{\lambda}$ phases which develops with increasing $x$. This developing dimer correlation reduces the number of unpaired ${\mathrm{Ti}}^{3+}$ ions, which makes the compound more conductive owing to the suppression of disorder for $x$ up to about 0.75. The dimer fluctuation causes a critical enhancement of the magnetic susceptibility at around 150 K in the $\ensuremath{\lambda}$ phase near the boundary ($x\ensuremath{\sim}0.9$) between the $\ensuremath{\lambda}$ and the $\ensuremath{\beta}$ phases. Such a correlation of the spin-singlet ${\mathrm{Ti}}^{3+}\text{\ensuremath{-}}{\mathrm{Ti}}^{3+}$ dimers may produce a high Seebeck coefficient in the conductive $\ensuremath{\alpha}$ and $\ensuremath{\lambda}$ phases leading to a large thermoelectric power factor at high temperatures.

We investigated the magnetic properties of Ba1−xLaxTbO3 with x ​= ​0, 0.1, and 0.2. The parent compound BaTbO3, which has single valent Tb4+ ions, undergoes an antiferromagnetic transition at the Neel temperature TN ​= ​33 ​K. Substitution of Ba2+ with La3+ reduces Tb4+ into Tb3+ and significantly enhances the magnetization (M) below around 25 ​K. The enhancement of the M can be explained by the formation of ferrimagnetic (FIM) or ferromagnetic (FM) clusters caused by a magnetic interaction between Tb4+ and Tb3+. At x ​= ​0.2, the TN merges into the onset temperature of the formation of the FIM or FM clusters.

We investigated Fe-substitution effects on ferromagnetic fluctuations in the superconducting overdoped and non-superconducting heavily overdoped regimes of the Bi-2201 cuprates by the magnetization and electrical-resistivity measurements. It was found that the spin-glass state was induced at low temperatures by the Fe substitution. The Curie constant and the effective Bohr magneton, estimated from the magnetic susceptibility, as well as the dimensionality of the ferromagnetic fluctuations from the resistivity, suggest the enhancement of the ferromagnetic fluctuations owing to the Fe substitution. A ferromagnetic spin-cluster model is proposed in the heavily overdoped regime of Bi-2201, while an antiferromagnetic spin-cluster model has been proposed in the overdoped regime of Bi-2201 [Hiraka et al., Phys. Rev. B 81, 144501 (2010)]., Comment: 5 pages, 4 figures

The electron-doped SrTiO3 exhibits good thermoelectric properties, which makes this material a promising candidate of an n-type oxide thermoelectric device. Recent studies indicated that only a few percent co-doping of La and Mn in SrTiO3 substantially reduces the thermal conductivity, thereby greatly improving the thermoelectric figure of merit at room temperature. Our time-of-flight neutron scattering studies revealed that by doping both La and Mn into SrTiO3, the inelastic scattering spectrum shows a momentum-independent increase in the low-energy spectral weight approximately below 10 meV. The increase in the low-energy spectral weight exhibits a clear correlation with thermal conductivity. The correlation is attributed to dynamical and local structural fluctuations caused by the Jahn-Teller instability in Mn3+ ions coupled with the incipient ferroelectric nature of SrTiO3, as the origin of the low thermal conductivity.

The electron-doped SrTiO3 exhibits good thermoelectric properties, which makes this material a promising candidate of an n-type oxide thermoelectric device. Recent studies indicated that only a few percent co-doping of La and Mn in SrTiO3 substantially reduces the thermal conductivity, thereby greatly improving the thermoelectric figure of merit at room temperature. Our time-of-flight neutron scattering studies revealed that by doping both La and Mn into SrTiO3, the inelastic scattering spectrum shows a momentum-independent increase in the low-energy spectral weight approximately below 10 meV. The increase in the low-energy spectral weight exhibits a clear correlation with thermal conductivity. The correlation is attributed to dynamical and local structural fluctuations caused by the Jahn-Teller instability in Mn3+ ions coupled with the incipient ferroelectric nature of SrTiO3, as the origin of the low thermal conductivity.

We studied the physical properties of ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{V}}_{13}{\mathrm{O}}_{18}$ single crystals, which exhibit three different phases caused by the orbital and charge degrees of freedom in V ${t}_{2g}$ states. We found from the magnetic susceptibility and the NMR measurement that the low-temperature phase of this series of compounds is characterized by the spin-singlet state. We also found from the electrical resistivity and optical conductivity spectra that these compounds become heavily anisotropic in the low-temperature phase with V trimerization, indicating that the orbital ordering of V ${t}_{2g}$ states causes the anisotropy of the electronic structure of this series of compounds.

We have investigated the magnetic properties of ${\mathrm{EuTi}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}{\mathrm{O}}_{3}$ with $0\ensuremath{\le}x\ensuremath{\le}1$ and established a detailed magnetic phase diagram. Substitution of ${\mathrm{Ti}}^{4+}$ with ${\mathrm{Al}}^{3+}$, which oxidizes magnetic ${\mathrm{Eu}}^{2+}$ $(J=7/2)$ into nonmagnetic ${\mathrm{Eu}}^{3+}$ $(J=0)$, turns the antiferromagnetic insulating ground state $(x=0)$ into the ferromagnetic (FM) insulating one $(0.10\ensuremath{\le}x\ensuremath{\le}0.50)$. The ${\mathrm{Eu}}^{2+}/{\mathrm{Eu}}^{3+}$ mixed valence is indispensable for the FM behavior. In $0.10\ensuremath{\le}x\ensuremath{\le}0.33$, the Curie temperature ${T}_{\mathrm{C}}$ has a plateau at $\ensuremath{\sim}4$ K, and the FM correlation is most enhanced around $x=0.25$. In $0.33\ensuremath{\le}x\ensuremath{\le}1,{\mathrm{Al}}^{3+}$ substitution suppresses the FM correlation due to the dilution of magnetic ${\mathrm{Eu}}^{2+}$ ions. Our present results would provide useful information for magnetoelectric phase control of ${\mathrm{EuTiO}}_{3}$-based compounds.

The luminescence properties of Eu2+-doped barium calcium silicon oxynitrides (general formula: Ba4-xCaxSi6ON10: Eu2+ (x= 1.8 ~ 2.2)) were examined, together with the preparation conditions for the solid state reaction. Firstly, the stoichiometric amounts of Ba, Ca3N2, SiO2 and Si3N4 were mixed with Eu2O3 (activator; the molar ratios of Eu to (Ca + Ba + Eu) (= m; 0.05 to 1.0)) for the preparation of Ba1.8Ca2.2Si6ON10: Eu2+, Ba2.0Ca2.0Si6ON10: Eu2+ and Ba2.2Ca1.8Si6ON10: Eu2+, and then the mixtures were heated at a temperature between 1300 and 1550°C for 10 h in N2 atmosphere. The single phase compounds, which were prepared by the heating at and above 1350°C, emitted the red color light whose wavelength could be changed from 638 to 653 nm with increasing m value from 0.05 to 1.00, due to the excitation at the wavelength of 528 nm.

Magnetic field dependence of magnetization and electric polarization in mono-domain crystals of BiFeO3 were studied in pulsed magnetic fields up to 56 T. The observed anisotropic transition fields were reasonably explained by Ginzburg–Landau theory at low temperatures, whereas their temperature dependence could not be in the simple model. The electric polarization measurements provide matrix elements of the linear magnetoelectric tensor | α 31 | ∼ | α 32 | = 1.5 ± 0.2 ps / m .

We have systematically investigated the magnetic and the dielectric properties of Eu0.595(Y1−x Ho x )0.405MnO3 (0 ≤ x ≤ 1) single crystals with fine tunning of 4f magnetic moments while keeping the average size of the rare-earth (R) site the same. In the x = 0.3 crystal, the ferroelectric polarization along the c axis (P c ) emerges at 25 K; then, P c is suppressed, and P a appears simultaneously with decreasing temperature. On further decreasing temperature, P a disappears and P c appears again. The observed reentrant behavior of the P c phase indicates that the P a and the P c phases are strongly competing with each other.

We study the effects of Zn substitution on single crystals of the low-dimensional multiferroic material Cu3Mo2O9. We report the magnetic field-temperature phase diagram obtained from the temperature and the magnetic field dependences of the specific heat, the dielectric constant, the differential magnetization, and the electric polarization-electric field curve in Cu2.85Zn0.15Mo2O9. We obtain three phases: a paraelectric and a ferroelectric phase, and a ferroelectric phase with a large coercive electric field. The origin of the last one is discussed based on the charge redistribution effect on a half-filled Mott insulator. In this phase, the Zn substitution induces a robust localized ferroelectric polarization that increases the coercive electric field.

The two-legged spin ladder Cu(CO3)0.5(ClO4)(H2O)0.5(NH3)2.5 consists of a rung formed by two Cu(II)’s and of a spacing molecule CO $_{3}^{2-}$ between each two rungs. The non-centrosymmetric shape of CO $_{3}^{2-}$ molecule brings a slight bond alternation along the leg, and hence the system can be considered as an alternating spin chain, which is confirmed so far by the temperature dependence of magnetic susceptibility. In order to investigate its spin state at low temperatures, we have performed experiments of 1H-NMR, magnetization and specific heat under wide range of magnetic field, and have found the critical diverging of longitudinal relaxation rate 1/T 1, the spectral broadening and the lambda-type anomaly in specific heat at T N≃ 3.4 K, indicating the existence of long range magnetic order. In paramagnetic state well above T N, 1/T 1 showed a power-law temperature dependence, suggesting the realization of Tomonaga Luttinger liquid state.

Strain, magnetization, dielectric relaxation, and unpolarized and polarized neutron diffraction measurements were performed to study the magnetic and structural properties of spinel Co1 amp; 8722;xV2 xO4. The strain measurement indicates that, upon cooling, amp; 916;L L in the order of amp; 8764;10 amp; 8722;4 starts increasing below TC, becomes maximum at Tmax, and then decreases and changes its sign at T . Neutron measurements indicate that a collinear ferrimagnetic order develops below TC and upon further cooling noncollinear ferrimagnetic ordering occurs below Tmax. At low temperatures, the dielectric constant exhibits a frequency dependence, indicating slow dynamics. These results indicate the existence of an orbital glassy state at low temperatures in this nearly metallic frustrated magnet. DOI 10.1103

We have investigated magnetic and dielectric properties of akermanite Sr2CoSi2O7 single crystal in which the orbital hybridization is controllable by external magnetic fields. Sr2CoSi2O7 shows the electric polarization that is originated from asymmetric orbital hybridization induced by magnetic field. This induced electric polarization was observed even at temperatures considerably higher than the magnetic transition temperature. The polarization data obtained for the paramagnetic phase are scaled with the square of the induced magnetization. By the discussion of the crystal symmetry, the space group of a polar state of akermanite materials is probably Cmm2.

The conditions for the preparation of regular-shaped Eu2+-doped calcium silicon nitride ((Ca0.99Eu0.01)2Si5N8) powder were examined by the carbothermal reduction and nitridation (CRN) of oxide/nitride powder prepared by ultrasonic spray pyrolysis. Two kinds of silicon sources, i.e., (i) colloidal silica (CS) and (ii) silicon nitride (Si3N4; SN), were used for the spray pyrolysis. Firstly, the solution containing 0.057 mol·m-3 Ca(NO3)2, 0.140 mol·dm-3CS and 5.71 x 10-4 mol·dm-3Eu(NO3)3 was spray-pyrolyzed at 600°C, and the resulting powder was calcined at 800°C for 10 min in air. The single phase but agglomerated particles of (Ca0.99Eu0.01)2Si5N8 were obtained when the CRN (the relative carbon amount to the stoichiometric amount (m): 1.5) of spray-pyrolyzed/calcined oxide powder was conducted at 1300°C for 2 h in nitrogen (N2) atmosphere. Secondly, the solution containing 0.0285 mol·dm-3Ca(NO3)2, 0.070 mol·dm-3SN and 2.855 x 10-4mol·dm-3Eu(NO3)3 (one-half of the solution concentration compared to the case of CS utilization) was spray-pyrolyzed, and the CRN of spray-pyrolyzed oxide/nitride powder was conducted at 1500°C for 2 h to obtain (Ca0.99Eu0.01)2Si5N8 in N2 atmosphere. The microscopic observation showed that this powder was composed of regular-shaped particles with sizes of approximately 2-3 µm. The excitation and emission peaks of this powder appeared at around 370 and 590 nm, respectively, showing the emission of orange light.

Large changes in the low-temperature specific heat (low-T C) by applying magnetic fields up to 9 Tesla were found in the lightly Mn-substituted electron-doped perovskites Sr1−xLaxTiO3. The changes in the low-T C are qualitatively well explained by the Schottky specific heat (CSch) of localized spins of the Mn 3d electrons in weak internal magnetic fields via itinerant electrons. According to the analysis by using the conventional model, the doped Mn ions are apparently not Mn4+ (S = 3/2) ions, but are Jahn-Teller active Mn3+ (S = 2) ions or mixtures of Mn3+ and Mn2+ ions. However, the actual numbers of localized spins estimated from CSch are about 30% smaller than the expected values. Part of the localized spins of the Mn 3d electrons may disappear due to Kondo coupling with the itinerant electrons, leading to the observed enhancement of the electronic specific heat coefficients.

We developed a high-speed polarizing microscope imaging system combined with a 37 T pulse magnet. With utilizing this system, we can visualize some kinds of structural transitions induced by high magnetic fields. The efficiency of this system was tested through observation of the field-induced collapse of charge-orbital ordering (COO) in mixed-valent manganites. In perovskite-type Nd1/2Sr1/2MnO3, quantitative analyses of the obtained polarizing microscope images clearly show the discontinuous change in birefringence accompanied with hysteresis, which are characteristic of the first order transitions. This observation of field-induced melting of the COO was also successful in a layered manganite La1/2Sr3/2MnO4 in which changes in magnetization and magnetoresistance at the transition are less clear. The present success in observation of the melting of the COO demonstrates the potential applicability of this system to visualize other kind of structural transitions even in a tiny piece of crystal.

A neutron diffraction study was performed on a single crystal of 4 f -moment-free perovskite manganite Eu0.595Y0.405MnO3 to elucidate the relation between the spontaneous ferroelectric polarization and the magnetic structure. Eu0.595Y0.405MnO3 shows an incommensurate magnetic ordering below T N = 47 K . The ferroelectric polarization P along the c axis appears below 25 K, and it is replaced by P along the a axis below 23 K. We have observed the change of magnetic structure at temperatures where the ferroelectric polarization appears and changes its polarization direction.

We have studied the chemical potential shift and changes in the electronic density of states near the Fermi level (E F) as functions of temperature and carrier concentration in Pr1−x Ca x MnO3 (PCMO) and Nd1−x Sr x MnO3 (NSMO) by measurements of photoemission spectra. Suppression of the chemical potential shift as a function of carrier concentration has been observed in PCMO and NSMO near and in the composition range where the CE-type antiferromagnetic charge-ordered (CO) phase appears at low temperatures. This result indicates that there is charge self-organization on a microscopic scale such as stripe formation in this composition range. In the ferromagnetic metallic phase of NSMO, we found a large temperature-dependent chemical potential shift at low temperatures and attributed this to double-exchange mechanism. Suppression of the temperature-dependent chemical potential shift near Curie temperature was observed, possibly associated with the formation of correlated polarons. In the valence band near the E F of PCMO, spectral weight was transferred with hole doping, leading to a finite intensity at E F even in the paramagnetic insulating phase above the CO phase for x≳0.3, and as the temperature was lowered, a clear gap opening was observed in the CO phase.

BiFeO3 is one of the most widely studied multiferroic materials, as it offers a strong coupling between magnetism and electric polarization up to room temperature. Here, studying monodomain crystals, the authors find an additional electric polarization component orthogonal to the widely studied one.

The magnon dispersion of Nd0.60Sr0.4MnO3 has been measured along the [q q q], [q q 0], and [0 0 q] propagation directions using inelastic neutron scattering. Modes attributed to both Mn–Mn interactions and Nd–Mn interactions were detected. At low temperatures, and for all three directions, the low q Mn–Mn dispersion closely followed a Heisenberg nearest-neighbor model calculation, before showing marked softening at higher values of q. For the [q q 0] and [0 0 q] directions, this softening appears to correspond with intersection with 20 and 40 meV phonon branches, respectively. At low temperatures, and for all three directions, the Nd–Mn dispersion followed the calculated Heisenberg dispersion for all measured points. Additionally, the temperature dependence of the magnon stiffness parameter D was measured up to T C = 273 K , and showed conventional temperature renormalization behavior.

The Hall resistivity and magnetization have been investigated in the ferromagnetic state of the bilayered manganite La(2-2x)Sr(1+2x)Mn2O7 (x=0.36). The Hall resistivity shows an increase in both the ordinary and anomalous Hall coefficients at low temperatures below 50K, a region in which experimental evidence for the spin glass state has been found in a low magnetic field of 1mT. The origin of the anomalous behavior of the Hall resistivity relevant to magnetic states may lie in the intrinsic microscopic inhomogeneity in a quasi-two-dimensional electron system., 7 pages, 4 figures, Solid State Communications (in press)

We have investigated the magnetic and the dielectric properties of akermanite Sr2CoSi2O7 and Sr2MnSi2O7 single crystals. Sr2CoSi2O7 shows a canted antiferromagnetism with a large magnetic anisotropy at temperatures below 7 K. By applying a magnetic field along the [110] direction, an electric polarization emerges along the c axis at temperatures below the magnetic transition temperature. In high magnetic fields, the saturation magnetization becomes enhanced only when the electric polarization appears. In contrast, the magnetization of Sr2MnSi2O7 is isotropic at all temperatures, and its magnetic-field-induced electric polarization is very small. These results suggest that the electronic configuration of the transition-metal ion is of crucial importance for the appearance of electric polarization.

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.

Magnetic and dielectric properties of \aa kermanite Ca$_2$CoSi$_2$O$_7$ single crystals were investigated in pulsed high magnetic fields. In magnetic fields along the $c$ axis, this material shows a magnetization plateau in a wide range of field below the saturation. Magnetization processes for fields along the $a$ and $b$ axes show multiple anomalies but different traces to each other, indicating the breaking of four-fold symmetry. Measurements of the magnetoelectric effects exhibit the changes in electric polarization according to the changes in the spin system. The experimentally determined quadratic magnetoelectric tensor is consistent with that expected in the crystal symmetry of orthorhombic $P2_12_12$., Comment: 11 pages, 5 figures

The magnetic and dielectric properties under high magnetic fields are studied in the single crystal of Cu3Mo2O9. This multiferroic compound has distorted tetrahedral spin chains. The effects of the quasi-one dimensionality and the geometrical spin frustration are expected to appear simultaneously. We measure the magnetoelectric current and the differential magnetization under the pulsed magnetic field up to 74 T. We also measure the electric polarization versus the electric field curve/loop under the static field up to 23 T. Dielectric properties change at the magnetic fields where the magnetization jumps are observed in the magnetization curve. Moreover, the magnetization plateaus are found at high magnetic fields.

We studied single crystals of $\text{BaV}{}_{13}$$\text{O}{}_{18}$, in which V ions with an average valence of +2.62 ($3{d}^{2.38}$) form a quasi-fcc lattice. We found that the ground state of the stoichiometric crystal is insulating, whereas that of the off-stoichiometric crystal is metallic with a large effective mass. This metallic state can be explained by the Kondo coupling between the magnetic moment existing at the lone V ion and itinerant carriers in the V tetramers.

Spacecraft usually expel excess heat into deep space with radiators, keeping the temperature of all the elements of a spacecraft system within the allowable limits for all mission phases. As the infrared emissivity of the radiator is constant, the temperature (T) of these components is affected by heat inputs which are highly variable with time over the life of the mission. Thus, some devices are required for active thermal control. The Smart Radiation Device (SRD) is one of the next generation thermal control materials for spacecrafts [1]. It is a light ceramic tile that changes its emissivity according to its own T. SRD makes use of perovskite-type magnetoresistive Mn oxides L 3+ 1-xB 2+ xMnO3 (L=lanthanides and B=alkaline earths) that show a drastic metal-to-insulator transition (MIT) with increasing T. Such an exceptional MIT allows these compounds to have low infrared emissivity () at low T’s due to metallic behavior and high  at high T’s due to insulating behavior and this change of  is suitable for a spacecraft radiator. The first SRD used for a spacecraft HAYABUSA (in operation 2003-2010) employed La0.775Sr0.115Ca0.11MnO3 which has a large change of  (from  0.63 at 353 K) across a MIT around the room temperature.

We have studied the phenomena relevant to charge/orbital ordering in perovskite manganites. In the three bandwidth controlled systems, La 0.7 (Sr 1− y Ca y ) 0.3 MnO 3 ( x =0.3), (Nd 1− y Sm y ) 0.55 Sr 0.45 MnO 3 ( x =0.45), and Pr 0.65 (Sr 1− y Ca y ) 0.35 MnO 3 ( 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 Sr 2 FeMoO 6 ( T C ∼420 K) have been studied by utilizing single crystals.

Pr(1--x)CaxMnO(3) and Nd(1--x)SrxMnO(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 magneto-optics and colossal magnetoresistance as a powerful new method.

We present the muon spin relaxation/rotation spectra in the multiferroic compound (Cu,Zn)$_{3}$Mo$_{2}$O$_{9}$. The parent material Cu$_{3}$Mo$_{2}$O$_{9}$ has a multiferroic phase below $T_{\rm N}$ = 8.0 K, where the canted antiferromagnetism and the ferroelectricity coexist. The asymmetry time spectra taken at RIKEN-RAL pulsed muon facility show a drastic change at $T_{\rm N}$. At low temperatures the weakly beating oscillation caused by the static internal magnetic fields in the antiferromagnetic phase was observed in Cu$_{3}$Mo$_{2}$O$_{9}$ and the lightly ($0.5\%$) Zn-doped sample. From the fitting of the oscillating term, we obtain the order parameter in these samples: ferromagnetic moment in two sublattices of antiferromagnet. In the heavily ($5.0\%$) Zn-doped sample, the muon-spin oscillation is rapidly damped. The frequency-domain spectrum of this sample suggests a formation of magnetic superstructure., 8 pages, 5 figures, in press in JPS Conf. Proc. as a part of USM2013 Proceedings

Muon spin relaxation (μ + SR) spectroscopy has been applied to study spin dynamics in the manganite single crystal Nd 0.5 Sr 0.5 MnO 3 . Critical slowing down of Mn spin fluctuations has been observed above the ferromagnetic ordering temperature T C ∼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.

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

We have peformed neutron diffraction measurements on melt-grown polycrystalline samples of ${\mathrm{Nd}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ $(0.49l~xl~0.75).$ 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 ${\mathrm{Nd}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ system 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 $x\ensuremath{\gtrsim}1/2,$ indicating that the energy difference between these two states is very small. We also found that the ${\mathrm{MnO}}_{6}$ octahedra are apically compressed in the CE-type and A-type AFM states due to the ${d(3x}^{2}\ensuremath{-}{r}^{2}{)/d(3y}^{2}\ensuremath{-}{r}^{2})$ or ${d(x}^{2}\ensuremath{-}{y}^{2})$ orbital ordering, whereas they are apically elongated by the rod-type ${d(3z}^{2}\ensuremath{-}{r}^{2})$ 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 x dependence strongly suggests the onset of charge ordering for either $x=4/5$ or $x=3/4.$

We have investigated the ferromagnetic spin fluctuations in Nd1/2Sr1/2MnO3, 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 discuss unusual behavior discovered in spin dynamics in the nearly half-doped manganite systems. Nd 0.45 Sr 0.55 MnO 3 is a metallic antiferromagnet, and exhibits very anisotropic spin wave dispersion relations. The ferromagnetic (FM) state of Pr 1/2 Sr 1/2 MnO 3 and Nd 1/2 Sr 1/2 MnO 3 also exhibit clear 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.

X-ray diffraction measurements have been performed on Nd 0.5 Sr 0.5 MnO 3 single crystals at various temperatures and magnetic fields. The temperature dependences of the lattice parameters show abr...