Structural, magnetic and electrical properties of single crystalline La_(1-x)Sr_xMnO_3 for 0.4 < x < 0.85

We report on structural, magnetic and electrical properties of Sr-doped LaMnO_3 single crystals for doping levels 0.4 < x < 0.85. The complex structural and magnetic phase diagram can only be explained assuming significant contributions from the orbital degrees of freedom. Close to x = 0.6 a ferromagnetic metal is followed by an antiferromagnetic metallic phase below 200 K. This antiferromagnetic metallic phase exists in a monoclinic crystallographic structure. Following theoretical predictions this metallic antiferromagnet is expected to reveal an (x^2-y^2)-type orbital order. For higher Sr concentrations an antiferromagnetic insulator is established below room temperature.Comment: 8 pages, 7 figure

Study of equilibrium carrier transfer in LaAlO3/SrTiO3 from an epitaxial La1 12x Sr x MnO3 ferromagnetic layer

Using x-ray magnetic circular dichroism and ab-initio calculations, we explore the La1-xSrxMnO3/LaAlO3/SrTiO3 (001) heterostructure as a mean to induce transfer of spin polarized carriers from ferromagnetic La1-xSrxMnO3 layer into the 2DEG (two-dimensional electron gas) at the LaAlO3/SrTiO3 interface. By out-of-plane transport measurements, the tunneling across the LaAlO3 barrier is also analyzed. Our results suggest small or vanishing spin-polarization for the 2DEG: magnetic dichroism does not reveal a neat signal on Ti atoms, while calculations predict, for the pristine stoichiometric interface, a small spin-resolved mobile charge of 2.5 x 10(13) cm(-2) corresponding to a magnetic moment of 0.038 mu(B) per Ti atom, tightly confined within the single SrTiO3 layer adjacent to LaAlO3. Such a small magnetization is hard to be detected experimentally and perhaps not robust enough to survive to structural disorder, native doping, or La1-xSrxMnO3 dead-layer effects. Our analysis suggests that, while some spin-diffusion cannot be completely ruled out, the use of ferromagnetic La1-xSrxMnO3 epilayers grown on-top of LaAlO3/SrTiO3 is not effective enough to induce robust spin-transport properties in the 2DEG. The examined heterostructure is nevertheless an excellent test-case to understand some fundamental aspects of the spin-polarized charge transfer in 2D wells

Chemical potential shift in La(1-x)Sr(x)MnO(3): Photoemission test of the phase separation scenario

We have studied the chemical potential shift in La(1-x)Sr(x)MnO(3) as a function of doped hole concentration by core-level x-ray photoemission. The shift is monotonous, which means that there is no electronic phase separation on a macroscopic scale, whereas it is consistent with the nano-meter scale cluster formation induced by chemical disorder. Comparison of the observed shift with the shift deduced from the electronic specific heat indicates that hole doping in La(1-x)Sr(x)MnO(3) is well described by the rigid-band picture. In particular no mass enhancement toward the metal-insulator boundary was implied by the chemical potential shift, consistent with the electronic specific heat data.Comment: 7 pages, 3 figures, to be published in Europhysics Letter

Existence of orbital polarons in ferromagnetic insulating La1−x_{1-x}Srx_xMnO3_{3} (0.11<x<<x<0.14) evidenced by giant phonon softening

We present an inelastic light scattering study of single crystalline (La$_{1-y}$Pr$_y$)$_{1-x}$Sr$_{x}$MnO$_3$ ($0\leq x\leq0.14$,$y=0$ and $x=1/8$,$0\leq y\leq0.5$). A giant softening up to 20 - 30 cm$^{-1}$ of the Mn-O breathing mode has been observed only for the ferromagnetic insulating (FMI) samples ($0.11\leq x \leq 0.14$) upon cooling below the Curie temperature. With increasing Pr-doping the giant softening is gradually suppressed. This is attributed to a coupling of the breathing mode to orbital polarons which are present in the FMI phase.Comment: 4 pages, 5 figure

Chemical potential shift induced by double-exchange and polaronic effects in Nd_{1-x}Sr_xMnO_3

We have studied the chemical potential shift as a function of temperature in Nd$_{1-x}$Sr$_x$MnO$_3$ (NSMO) by measurements of core-level photoemission spectra. For ferromagnetic samples ($x=0.4$ and 0.45), we observed an unusually large upward chemical potential shift with decreasing temperature in the low-temperature region of the ferromagnetic metallic (FM) phase. This can be explained by the double-exchange (DE) mechanism if the $e_g$ band is split by dynamical/local Jahn-Teller effect. The shift was suppressed near the Curie temperature ($T_C$), which we attribute to the crossover from the DE to lattice-polaron regimes.Comment: 5 pages, 6 figure

Giant Tunneling Electroresistance Effect Driven by an Electrically Controlled Spin Valve at a Complex Oxide Interface

A giant tunneling electroresistance effect may be achieved in a ferroelectric tunnel junction by exploiting the magnetoelectric effect at the interface between a ferroelectric barrier and magnetic La1-xSrxMnO3 electrode. Using first-principles density functional theory we demonstrate that a few magnetic monolayers of La1-xSrxMnO3 near the interface act, in response to ferroelectric polarization reversal, as an atomic scale spin-valve by filtering spin-dependent current. This effect produces more than an order of magnitude change in conductance, and thus constitutes a giant resistive switching effect.Comment: 4 pages, 4 figure

Magnetic Transition Temperature of (La,Sr)MnO3_3

Using the Kondo lattice model with classical spins in infinite dimension, magnetic phase transition in the perovskite-type $3d$ transition-metal oxide (La,Sr)MnO$_3$ is theoretically studied. On the Bethe lattice, the self-consistency equations are solved exactly. Curie temperatures at the region of double-exchange ferromagnetism $0.1 < x < 0.25$ as well as the Neel temperature at $x=0$ are well reproduced quantitatively. Pressure effect on the Curie temperature is also discussed.Comment: 7 pages, 1 PS file with 3 figures appended at the end, LaTe