# J. E. Crow's research while affiliated with The National High Magnetic Field Laboratory (National MagLab) and other places

## Publications (348)

Article
Results of the high-frequency/field electron spin resonance investigation of the quantum S = 1/2 chain compound LiCu2O2 are presented. Spin-singlet ground state (which occurs in LiCu2O2 as a result of the spin-dimerization) is revealed at a temperature above T ~ 23 K. The size of the gap between the spin-singlet ground state and the excited triplet...
Article
Well characterized single crystals of the four layer crystallographic form of BaRuO3 were studied at low temperatures (20 < T < 850 mK) and high magnetic fields (0 < H < 30 T). Quantum oscillations have been observed via the Shubnikov - de Haas and de Haas - van Alphen effects. In marked contrast, BaRuO3 with the nine-layer structure shows no simil...
Article
Zn substitution for Cu in YBa2Cu3O7 rapidly reduces the superconducting transition temperature, Tc. Superconductivity is quenched between x=0.08 (T =30 K) and x=0.10. The normal state paramagnetism grows with Zn substu-tition, presumably due to increased localization on the Cu sublattice. Susceptibility studies of oxygen depleted (nonsuperconductin...
Article
Solutions of Y, Ba and Cu nitrate were spray-frozen. Very small particles consisting of atomic mixtures of these salts remained after the water was sublimed. These YBCO precursors were characterized and their behavior was studied in detail while they were thermally decomposed by a variety of techniques. Kilogram size batches are routine. The final...
Article
High quality bulk YBa2CuOx−7 was synthesized by fusing stoichiometric amounts of yttrium and copper nitrates and barium hydroxide, in air, using an ordinary Bunsen burner. The starting materials go through a short-lived liquid phase yielding a solid black product which was subsequently heat treated, (900 C, 18–24 h, in air, followed by 500 C, 5 h.,...
Article
The temperature and concentration dependence of the electron paramagnetic resonance spectra of YBa2(Cu1−xZnx)3O7 has been measured for 0≤x≤0.16. Zn substituted on the Cu-site cause a rapid nearly linear depression of the superconducting transition temperature Tc with Tc going to zero in the vicinity of x=0.10. Only weak EPR spectra due to ≤1% of th...
Article
Optical spectra of nine-layer BaRuO3 show clear electrodynamic response changes due to a pseudogap formation. As temperature decreases, the pseudogap formation induces a gradual reduction of carrier density n and an abrupt suppression of scattering rate 1/τ. It was found that the competition between n and 1/τ can induce a crossover from metallic to...
Article
A comparative study of EuBaCo2O5+δ (Eu‐112) single crystals grown from a high temperature flux melt by two different approaches is presented. The magnetization and magnetoresistance (MR) of the single crystals were measured over a wide range of dc magnetic field. These data for the both types of crystals imply a strong correlation between the spi...
Article
Full-text available
We report recent transport and thermodynamic experiments over a wide range of temperatures for the Mott-like system Ca3Ru2O7 at high magnetic fields, B, up to 30 T. This work reveals a rich and highly anisotropic phase diagram, where applying B along the a-, b-, and c-axis leads to vastly different behavior. A fully spin-polarized state via a first...
Article
Srn+1RunO3n+1 represents a class of layered materials whose physical properties are a strong function of the number of Ru–O layers per unit cell, n. These materials along with the paramagnetic CaRuO3 shares two major characteristics, namely, robust Fermi liquid behavior at low temperatures and anomalous transport behavior featured by linear tempera...
Article
Full-text available
The magnetization, resistivity, and magnetoresistance (MR) of single crystals of GdBaCo2O5.5 and EuBaCo2O5.5 are measured over a wide range of dc magnetic fields (up to 30T ) and temperature. In LBaCo2O5.5 (L=Gd,Eu) , the Co ions are trivalent and can exist in three spin states, namely, the S=0 low-spin (LS) state, the S=1 intermediate-spin (IS) st...
Article
GdBaCo2O5+δ is an oxygen deficient perovskite system possessing a rich magnetic phase diagram. Magnetization, M(T), measured on GdBaCo2O5+δ single crystals reveals significant anisotropy along different crystal orientations. M(T) data show several magnetic regimes associated with different Co3+ spin states as well as dramatic differences for H appl...
Article
Full-text available
The specific heat and electrical resistivity of Sr3Ru2O7 single crystals are measured in several magnetic fields applied along the c axis for temperatures below 2 K and at fields up to 17 T. Near the critical metamagnetic field at B*1˜7.8 T, the electronic specific heat divided by temperature increases logarithmically as the temperature decreases,...
Article
The 4d-electron based ruthenates, Srn+1RunO3n+1 (n=1, 2, 3 and infinity) are correlated electron systems characterized by ground states that are highly dependent on the interplay between spin, charge, lattice and orbital degrees of freedom. These materials, which represent another example of nature’s engineered layered systems, exhibit astonishing...
Article
We report magnetic and transport properties of single crystal Sr3Ir2O7, a bilayered orthorhombic system with Bbca symmetry. Our study reveals that Sr3Ir2O7 is a ferromagnetic insulator with a Curie temperature of 285 K and a small ordered magnetic moment. The saturation moment is found to be less than 4S=1/2. For fields larger than 1T the magnetic...
Article
Full-text available
Uniaxial strain can be applied to a sample in a standard piston-cylinder type pressure cell provided that the sample is constrained in such a way as to prevent any expansion or contraction in the plane perpendicular to the direction of the applied force. This can be accomplished by replacing the normal fluid based pressure media with a loaded epoxy...
Article
Resistivity of the bilayered ruthenate Sr_3Ru_2O7 was measured at a series of angles between 0^o (H bot c) and 90^o (H \vert \vert c) as a function of field and temperature for 20mK < T < 800mk and H T^* , resistivity with an exponent less than two is observed, which is common in non-Fermi liquid (NFL) systems. Angular dependent magnetoresistivity...
Article
The Ca3Ru2O7 with a Mott-like transition at 48 K and a Neel temperature at 56 K features different in-plane anisotropies of magnetization and magnetoresistance. Applying the magnetic field along the magnetic easy axis precipitates a spin-polarized state via a first-order metamagnetic transition but does not lead to full suppression of the Mott stat...
Article
Full-text available
Ca3Ru2O7 with a Mott-like transition at 48 K and a Néel temperature at 56 K features different in-plane anisotropies of the magnetization and magnetoresistance. Applying a magnetic field along the magnetic easy-axis precipitates a spin-polarized state via a first-order metamagnetic transition, but does not lead to a full suppression of the Mott sta...
Article
Text (Electronic thesis) in PDF format. Mode of access: World Wide Web. Advisor: Dr. Jack Crow, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed Jan 18, 2005). Thesis (Ph. D.)--Florida State University, 2004. Includes bibliographical references.
Article
Specific heat of Sr_3Ru_2O7 single crystals was measured in several magnetic fields applied along the c-axis for 0.07 K < T < 2 K. Near the critical metamagnetic field at H_1^* ˜ 7.8 T, the coefficient of electronic specific heat, gamma , diverges over a large region of temperature before saturating, indicating a crossover from a non-Fermi liquid r...
Article
The National High Magnetic Field Laboratory (NHMFL) operates three facilities in support of magnet-related research. The main facilities are located at Florida State University, Tallahassee, Florida, the ultra-low-temperature high-magnetic-field facilities are located at the University of Florida, Gainesville, Florida, and the pulsed field faciliti...
Article
Full-text available
We report magnetic and interplane transport properties of Ca3Ru2O7 at high magnetic fields and low temperatures. Ca3Ru2O7 with a bilayered orthorhombic structure is a Mott-like system with a narrow charge gap of 0.1 eV. Of a host of unusual physical phenomena revealed in this study, a few are particularly intriguing: (1) a collapse of the c-axis la...
Article
Ca3Ru2O7, a Mott-like system with a narrow charge gap of 0.1 eV, is characterized by strong coupling between different degrees of freedom and various magnetic and electronic transitions that are abrupt and highly anisotropic. In this paper, we report a host of physical phenomena including: (1) A collapse of the c-axis lattice parameter at a metal–n...
Article
We have studied the microstructures of single crystals of the bi- and triple-layered transition metal oxides grown from high-temperature solution, the Ca- or the Sr-ruthenates that belong to the Ruddelsden–Popper series by transmission electron microscopy. The single crystals usually have rectangular shape with the facets on basal plane and the {11...
Article
Ca3Ru2O7 is a bilayered metallic paramagnet that orders antiferromagnetically at TN=56K while remaining metallic and then undergoes a spin reorientation coincident with a metal-nonmetal transition at TM=48K, entering a metamagnetic state. Low-temperature specific-heat measurements in magnetic fields show that the electronic specific heat, γ=44mJ/mo...
Article
SrRuO3 is a highly correlated narrow d-band oxide which has a ferromagnetic transition at Tc = 165K. Correlated oxide systems in general, and SrRuO3 in particular, have been studied extensively over the past several years. However, with exception of the high Tc superconductors which have been extensively studied with Angular Resolved Photoemission...
Article
Ca3Ru2O7 is a bilayered metallic paramagnet that orders antiferromagnetically at TN = 56 K while remaining metallic and then undergoes a spin reorientation coincident with a metal-nonmetal transition at TM = 48 K, entering a metamagnetic state. Low-temperature specific-heat measurements in magnetic fields show that the electronic specific heat, γ=...
Article
Magnetization, resistivity, and specific heat measurements were performed on GdBaCo_2O_5+delta single crystals for the first time revealing significant anisotropy along different crystal orientations. M(T) data show several magnetic regions associated with different Co^3+ spin states as well as dramatic differences for H applied parallel and perpen...
Article
Specific heat, resistivity, and magnetization have been measured through the ferromagnetic critical point for single-crystal ${\mathrm{SrRuO}}_{3}.$ All data are well fitted to small reduced temperatures with mean-field critical exponents including Gaussian fluctuations. The specific heat and temperature derivative of resistivity scale with each ot...
Conference Paper
When the optical conductivities of the normal and superconducting states are compared, one observes that there is a transfer of spectral weight from finite frequencies to the zero-frequency delta-function conductivity of the superconductor. The strength of this delta function gives the superfluid density, rho_s. In a metallic superconductor the fre...
Article
Full-text available
We report the interplane resistivity, ρc, at high magnetic fields B, with different orientations together with structural and magnetic properties of bilayered Ca3Ru2O7, a Mott-like system with a gap of 0.1 eV. A wide array of conventionally unanticipated phenomena revealed in this work includes (1) a collapse of the c-axis lattice parameter at a me...
Article
We report a Raman scattering study of the pressure-induced collapse of the Mott-like phases of Ca3Ru2O7 (T(N)=56 K) and Ca2RuO4 (T(N)=110 K). The pressure dependence of the phonon and two-magnon excitations in these materials indicate (i) a T approximately 0 pressure-induced collapse of the antiferromagnetic (AF) insulating phase above P(*) approxi...
Article
We report magnetic and transport properties of single-crystal Sr3Ir2O7, a bilayered orthorhombic system with Bbca symmetry. Our study reveals that Sr3Ir2O7 is a ferromagnetic insulator with a Curie temperature of TC=285K and a small ordered magnetic moment. The saturation moment μS is found to be less than 0.04μB/Ir or 4% of the expected moment for...
Article
The rare-earth ruthenate Pr3RuO7 is a Mott insulator displaying magnetic ordering at two temperatures TN1 = 36 K and TN2 = 55 K. By substituting diamagnetic La for Pr and diamagnetic Nb for Ru, TN1 is shown to be associated with ordering among the rare earths and TN2 among the Ru cations. These results are similar to those of Sm3RuO7, but the order...
Article
The rare-earth ruthenate Pr3RuO7 is a Mott insulator displaying magnetic ordering at two temperatures TN1 = 36 K and TN2 = 55 K. By substituting diamagnetic La for Pr and diamagnetic Nb for Ru, TN1 is shown to be associated with ordering among the rare earths and TN2 among the Ru cations. These results are similar to those of Sm3RuO7, but the order...
Article
Well characterized single crystals of the four layer crystallographic form of BaRuO3 were studied at low temperatures (20 < T < 850 mK) and high magnetic fields (0 < H < 30 T). Quantum oscillations have been observed via the Shubnikov - de Haas and de Haas - van Alphen effects. In marked contrast, BaRuO3 with the nine-layer structure shows no simil...
Article
Results of the high-frequency/field electron spin resonance investigation of the quantum S=1/2 chain compound LiCu2O2 are presented. Spin-singlet ground state (which occurs in LiCu2O2 as a result of the spin-dimerization) is revealed at a temperature above T ~ 23 K. The size of the gap between the spin-singlet ground state and the excited triplet i...
Article
Results of systematic structural, magnetic, electron-spin resonance, and specific-heat investigations of the S=1/2 quantum antiferromagnet compound LiCu2O2 are presented. A spin-singlet ground state is revealed at temperatures above T∼23K. In this temperature region LiCu2O2 may be regarded as a quantum S=1/2 chain with competing nearest- and next-n...
Article
Results of systematic structural, magnetic, electron-spin resonance, and specific-heat investigations of the S = 1/2 quantum antiferromagnet compound LiCu2O2 are presented. A spin-singlet ground state is revealed at temperatures above T ∼ 23 K. In this temperature region LiCu2O2 may be regarded as a quantum S = 1/2 chain with competing nearest- and...
Article
We report the specific heat as a function of temperature in zero applied magnetic field for three magnetic systems (α-Co[N(CN)2]2, β-Co[N(CN)2]2, Ni[N(CN)2]2) and two nonmagnetic systems (Cu[N(CN)2]2, Zn[N(CN)2]2). The anomalies revealed by the magnetic contribution to the specific heat are associated with the onset of long-range order. The transit...
Article
Full-text available
We report a Raman scattering study of the pressure-induced collapse of the Mott-like phases of Ca_3Ru_2O_7 (T_N=56 K) and Ca_2RuO_4 (T_N=110 K). The pressure-dependence of the phonon and two-magnon excitations in these materials indicate: (i) a pressure-induced collapse of the antiferromagnetic (AF) insulating phase above P* ~ 55 kbar in Ca_3Ru_2O_...
Article
Full-text available
Ca$_3$Ru$_2$O$_7$ undergoes an antiferromagnetic transition at $T_{\text{N}}=56$K, followed by a Mott-like (MI) transition at $T_{\text{MI}}=48$ K. This nonmetallic ground state, with a charge gap of 0.1 eV, is suppressed by a highly anisotropic metamagnetic transition that leads to a fully spin-polarized metallic state. We report the observation...
Article
Full-text available
We investigated the temperature dependence of the Raman spectra of a nine-layer BaRuO3 single crystal and a four-layer BaRuO3 epitaxial film, which show pseudogap formations in their metallic states. From the polarized and depolarized spectra, the observed phonon modes are assigned properly according to the predictions of group theory analysis. In...
Article
Advancements in condensed matter science have been primarily driven by the discovery and refinement of new materials and innovative approaches to characterization tools. There are many examples where advances in spectroscopic techniques including electron and magnetic resonance, new and more accessible approaches to phase space (pressure, magnetic...
Article
Ca3Ru2O7 is a Mott-like system with a narrow charge gap of 0.1eV. It is characterized by abrupt temperature or field induced transitions that separate a variety of magnetic and electronic phases, which are highly anisotropic. Ca3Ru2O7 undergoes an antiferromagnetic transition at TN=56 K and a metal-nonmetal transition at TMI=48 K with a unique anti...
Article
BaIrO3 is a nonmetallic weak ferromagnet with an exotic ground state. Recent experimental studies reveal evidence for a simultaneous onset of weak ferromagnetism and charge density wave formation at Tc=175 K, an unexpected occurrence that is also supported by results of tight-binding band structure calculations, which show partially nested pieces o...
Article
SrRuO3 is an itinerant ferromagnet (TC = 165K) and narrow d-band metal in which the physical properties are highly sensitive to slight changes in the structure. Doping Na onto the Sr site impacts this system in two ways: distorting the structure and reducing the number of electrons in the system. Measurements of the magnetic susceptibility, resisti...
Article
The experimental picture of the magnetism in the double-layered ruthenate Sr3Ru2O7 (with both the ferromagnetic and antiferromagnetic correlations present) could be consistent with the spin arrangement where the Ru ions in a layer (bilayer) are ferromagnetically aligned, but the layers (bilayers) are coupled antiferromagnetically. Since the effects...
Article
Nickel tapes which were cold rolled to large deformation and annealed to produce a cube texture were used as substrates for YBCO coated conductor development. In this study the cold rolled Nickel was annealed in 4%H2-Ar at 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, and 1050 °C for various times. After annealing, grain size and grain boundary (GB) gro...
Article
Pseudogap phenomena have been an interesting issue in strongly correlated systems, especially high-Tc cuprates. In 4d transition metal oxides, for the first time, we introduce BaRuO3 systems as a new kind of systems exhibiting the pseudogap phenomena. Compared with high-Tc cuprates, a development of the pseudogap as well as the coherent component i...
Article
We measured temperature-dependent reflectivity spectra of non-perovskite nine layer BaRuO3 single crystal and four layer BaRuO3 epitaxial film. In optical conductivity spectra obtained through Kramers–Kronig transformation, we observed that both materials show pseudogap formations in their metallic states. A clear development of pseudogap as well a...
Article
Ca2RuO4 is an antiferromagnetic insulator with a Neel temperature at TN=110K and a Mott transition at TMI=357K. Slight substitution of trivalent La for divalent Ca in Ca2RuO4 not only drastically reduces TMI but also simultaneously precipitate robust ferromagnetism in the antiferromagnetic host. It is believed that the ferromagnetic behavior is clo...
Article
RE2RuO5 (R=Nd,Sm,Eu,Gd,Tb) is a new class of materials, and is found to be insulating and magnetically ordered with an ordering temperature varying from 8 to 21K. The magnetic ground state is likely to be antiferromagnetic with a canted spin structure that leads to ferromagnetic behavior. The saturation moment is suppressed particularly for Gd2RuO5...
Article
In order to develop alternative buffer layers for YBCO coated conductors, RE<sub>2</sub>O<sub>3</sub> (RE=La, Pr, Sm, Eu, Gd, Tb, Ho, Yb, and Lu) thin films were studied as candidate materials. Buffer layers were grown on Ni tapes using organometallic compounds that are 2,4-pentanedionates, isopropoxides, and acetates by a continuous, non-vacuum so...
Article
Sr2YRuO6 is a magnetic insulator with a double-perovskite structure derived from the perovskite SrRuO3, which is an itinerant ferromagnet. Measurements of the magnetic susceptibility, magnetization, and electrical resistivity are performed on newly synthesized single crystals of Sr2YRuO6. The system orders antiferromagnetically at TN=26K and yet sh...
Article
Polycrystalline samples of the lanthanide ruthenate series L2RuO5 (L=Pr, Nd, Sm, Gd, and Tb) magnetically order in the range 8<T<24K with the ordering involving both the L and Ru cations. The series has a complex orthorhombic structure (space group Pnma) possessing chains of RuO5 five oxygen coordinated square pyramids which are corner-sharing and...
Article
BaRuO3 is a quasi one dimensional metal which displays unusual and highly anisotropic transport behavior. Magnetic susceptibility and transport properties of high quality single crystals of the nine-layer crystallographic form of BaRuO3 have been measured over the temperature range of 30 mK to 1000 K. Of particular interest are (1) the appearance o...
Article
The magnetic and transport properties of Pr_3RuO7 along with impurity doped compounds have been investigated. The structure of Pr_3RuO7 is believed to be a quasi 1-D system characterized by corner-sharing RuO6 octahedra chains along the c-axis. Pr_3RuO7 is an insulator and antiferromagnetically orders at T_N1=55K and T_N2=36K. La(4f^0) and Nb(4d^0)...
Article
Gd_2RuO5 is a member of a recently investigated series of rare earth ruthenates possessing a complex orthorhombic structure consisting of edge-sharing 7-fold coordinated Gd sites and trans-corner-sharing chains of RuO5 square pyramids. Measurement of the magnetization and specific heat on polycrystalline samples indicate that the Gd ions order magn...
Article
In the insulating rare earth-transition metal oxide series R_2RuO_5, magnetic coupling is associated with both cation species. For R=Gd and Tb, (T_M=10 K and 18 K, respectively), the ordering is likely canted antiferromagnetic. For R=Pr (T_M= 8 K) ordering is spin glass-like, related to the partly structural frustration of the lattice. Field induce...
Article
LiCu_2O2 is a compound with double chain Cu^2+ copper ions separated in pairs by Li and Cu^1+ that forms a spin ladder or zig-zag chain system depending on the relative J's. The orthorhombic single crystals are highly twinned as determined by TEM. Magnetization and specific heat show ladder behavior above a transition near 25 K, suggestive of a fir...
Article
The H–T–J phase diagram of superconducting Ba1−xKxBiO3−y (x=0.37, 0.41, 0.5) single crystals has been studied by means of SQUID and cantilever force magnetometry. Strong upward curvature of the Hc2(T) dependence confirms at least intermediate strength of the electron–phonon coupling in this 3D-superconductor family. The normalized critical current...
Article
Full-text available
As carriers are introduced into the cuprates (by doping the insulating "parent" compounds) spectral weight appears in the optical spectrum at photon energies below the charge-transfer gap. This spectral weight increases as the doping level increases. Magnetic penetration depth measurements have shown a good correlation between superfluid density an...
Article
The hyperfine magnetic field in the ferromagnetic metal, SrRuO3, has been measured from 4.2 to 166.3 K by the 99Ru Mossbauer effect. The hyperfine field at 4.2 K is determined to be 33.0(0.4) T with an isomer shift of -0.33(.02) mm/s. The Curie temperature is determined 162(2) K for a polycrystalline sample. This is consistent with the determinatio...
Article
Ca3Ru2O7 is a Mott-like system with a narrow gap (≈0.1 eV). Very dilute doping of trivalent La (⩽5%) for divalent Ca prompts rapid and simultaneous changes in both the magnetic and transport properties, unambiguously illustrating the strong spin-charge coupling that characterizes Ca3Ru2O7. The antiferromagnetic metallic phase unique to Ca3Ru2O7 per...
Article
Ca_3Ru_2O7 is a Mott system with an antiferromagnetic transition at TN = 56 K and a sharp metal-insulator transition at TM = 48 K. As hydrostatic pressure is applied to the system, both TN and TM increase rapidly in temperature, although with quite different rates. The results of magnetic susceptibility and electrical resistance at pressures up to...
Article
Ca_3Ru_2O7 is a "badly" conducting metal having rho (T) ∝ T at high temperatures. It orders antiferromagnetically at T_N=56 K and undergoes a metal to insulator transition at T_M=48 K. The magnetic and electronic phase transitions of Ca_3Ru_2O7 are suppressed uniformly and rapidly by only very small substitution of the divalent Ca by the trivalent...
Article
Magnetic properties of the linear chain system LiCu_2O_2--T. Caldwell, P. L. Kuhns, A. P. Reyes, W. G. Moulton, G. Cao, S. McCall, and J. E. Crow, NHMFL X-ray diffraction studies show the LiCu_2O2 structure has two interacting perpendicular Cu^3+ chains isolated from the next plane of chains. The magnetization deviates appreciably from the Bonner-F...
Article
Ca_2RuO4 is a Mott system with a structurally driven metal-insulator transition at T_MI=357 K and a Néel temperature at T_N=110 K. Slight substitution of trivalent La for divalent Ca in Ca_2RuO4 drastically reduces T_MI and the electrical resistivity, simultaneously precipitating robust ferromagnetism in the antiferromagnetic host. TC is conspicuou...
Article
We present magnetization and electrical resistivity ρ data of single crystalline calcium hexaborides. The samples were grown from Ca rich (Ca_1+δB_6) and Ca deficient (Ca_1-δB_6) aluminum melts in order to study the influence of deviations form the exact stoichiometry on the electronic properties. The samples grown with excess Ca are diamagnetic. B...
Article
Ca_3Ru_2O7 is a double layered quasi-perovskite metal that orders antiferromagnetically at 56K and then undergoes a spin reorientation at 48K in conjunction with a metal to insulator transition(MIT). At low temperatures, this system undergoes a first order metamagnetic transition in a magnetic field of 6T applied along the easy axis, with a corresp...
Article
We measured reflectivity spectra of 9-layered BaRuO3 single crystal in the temperature(T) range of 10 to 500 K. T-dependent optical conductivity spectra, obtained through Kramers-Kronig transformation, exhibited the unexpected gap-like feature in the far-infrared region below 0.1 eV. Though its metallic state retains down to 80 K in dc resistivity,...
Article
We report neutron diffraction, magnetic and specific heat studies of the isomorphous M[N(CN)_2]2 (M = Mn, Fe). The crystal structure consists of axially elongated and successively tilted discrete octahedra. There are two antiferromagnetically coupled and spontaneously canted sublattices. The spin orientation is mainly along the a-axis with small un...
Article
We report a Raman scattering study of the relationship among the charge, spin, and lattice dynamics of Ca_3Ru_2O_7. The metal-insulator (MI) transition (T_MI 48 K) in this compound manifests inself as a rapid suppression of low-frequency electronic scattering intensity, reflecting the opening of a charge gap, Deltac 760 cm-1, and a concomitant soft...
Article
Orthorhombic Re_2RuO5 (Re=Y or rare earth ion) are a new class of materials, and have all been found to be ferromagnetic insulators with TC varying from 20 to 25 K. Preliminary results of our study indicate that the magnetic properties are chiefly dominated by 4d-electrons and/or d-f electron coupling. Characteristic of ruthenates, these materials...
Article
Sr_3Ru_2O7 is a member of the Ruddeldson and Popper series with n=2, and has a slightly distorted perovskite structure. Magnetization measurements on samples used in these experiments show ferromagnetic ordering with T_c=105 K and a spin rearrangement at 66 K. X-ray diffraction shows no evidence of any second phase. The zero field ^99,101Ru NMR has...
Article
Sr_3Ru_2O7 is a highly correlated narrow d-band itinerant ferromagnet with T_C=105K. In contrast Ca_3Ru_2O_7, a structural isomorph, is antiferromagnetic (T_N=56K) and undergoes a metal to non-metal transition at T_M=48K. A systematic transport and thermodynamic study of single crystal (Sr_1-xCa_x)_3Ru_2O7 for 0<= x<= 1 reveals an evolution of magn...
Article
Ca2RuO4 is a Mott system with a structurally driven metal-insulator transition at TMI=357 K and Néel temperature at TN=110 K. Slight substitution of trivalent La for divalent Ca in Ca2RuO4 drastically reduces TMI and the electrical resistivity, simultaneously precipitating robust ferromagnetism in the antiferromagnetic host. TC is conspicuously and...
Article
The magnetic, transport, optical, and structural properties of quasi-one-dimensional BaIrO3 show evidence for the simultaneous onset of electronic density wave formation and ferromagnetism at Two additional features in the chain direction dc conductivity show a sudden change to metallic behavior below and then a Mott-like transition at Highly non-l...
Article
In clean metallic superconductors, 100% of the mobile carriers participate ill the condensate, so that the London penetration depth (which measures the electromagnetic screening by the superconductor) indicates charge densities comparable to those inferred from the free-carrier plasma frequency. In the cuprates, this is not the case, even though pe...
Article
this report is based. In these cases the M-O-M bond angle may be considerably less than the ideal 180
Article
Full-text available
We report a first-order phase transition at TM=357 K in single-crystal Ca2RuO4, an isomorph to the superconductor Sr2RuO4. The discontinuous decrease in electrical resistivity signals the near destruction of the Mott insulating phase and is triggered by a structural transition from the low-temperature orthorhombic to a high-temperature tetragonal p...
Article
We report a Raman-scattering study of the relationship among the charge, spin, and lattice dynamics of CaâRuâOâ. The metal-insulator (MI) transition (T{sub MI}â¼48 K) in this compound manifests itself as a rapid suppression of low-frequency electronic scattering intensity, reflecting the opening of a charge gap, Î{sub c}â¼760 cmâ»Â¹, and a concomi...
Article
This paper presents a brief review of recent experimental results of the layered ruthenates (Sr, Ca)n+1,RunO3n+1, with n=1, 2, 3 and ∞ (n=number of Ru–O layers). With the layered nature of the crystal structures and the extended characteristic of the 4d-electrons, these ruthenates provide a truly unique opportunity to study not only the evolution o...
Article
SrRuO3 is an itinerant ferromagnet with TC = 165 K and CaRuO3 is a metallic paramagnet down to at least 30 mK. These materials are known to be narrow d-band metals, the physical properties of which are highly sensitive to small perturbations such as chemical doping. In this article, we report results of resistivity, specific heat, and magnetic susc...
Article
Full-text available
We report on the ab-plane optical reflectance measurements of single crystals of Y-doped Bi2Sr2CaCu2O8+delta and Pr-doped YBa2Cu3O7-delta over a wide frequency range from 80 to 40 000 cm(-1) (10 meV-5 eV) and at temperatures between 20 and :300 K. Y and Pr doping both decrease the hole concentration in the CuO2 planes. This has allowed us to invest...
Article
The temperature dependence of the electrical resistivity of two chemically substituted Ca-ruthenates is examined with the Efros-Shklovskii mechanism invoking Coulomb interactions between carriers. Additional mechanisms causing an energy dependence to the density of states at the Fermi surface may explain the unusually wide temperature and conductiv...
Article
Magnetization and magnetoresistivity of as-grown, oxygenated, and argon annealed single crystals of Ca3Ru2O7 are presented for 5<T<300 K and 0<H<7 T. As-grown Ca3Ru2O7 has been shown to have an antiferromagnetic metallic phase for 48<T<56 K and 0<H<4 T, located between the high-temperature paramagnetic metallic and the low-temperature antiferromagn...