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Bilayers of the oxide 3d ferromagnet La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) and the 5d paramagnet SrIrO$_{3}$ (SIO) with large spin-orbit coupling (SOC) have been investigated regarding the impact of interfacial SOC on magnetic order. For the growth sequence of LSMO on SIO, ferromagnetism is strongly altered and large out-of-plane-canted anisotropy associated with lacking magnetic saturation up to 4 T has been observed. Thin bilayer films have been grown coherently in both growth sequences on SrTiO$_3$ (001) by pulsed laser deposition and structurally characterized by scanning transmission electron microscopy (STEM) and x-ray diffraction (XRD). Measurements of magnetization and field-dependent Mn L$_{2,3}$ edge x-ray magnetic circular dichroism (XMCD) reveal changes of LSMO magnetic order which are strong in LSMO on SIO and weak in LSMO underneath of SIO. We attribute the impact of the growth sequence to the interfacial lattice structure/symmetry which is known to influence the interfacial magnetic coupling.

Atomically flat interfaces between ternary oxides have chemically different variants, depending on the terminating lattice planes of both oxides. Electronic properties change with the interface termination which affects, for instance, charge accumulation and magnetic interactions at the interface. Well-defined terminations have yet rarely been achieved for oxides of ABO3 type (with metals A, B). Here, we report on a strategy of thin film growth and interface characterization applied to fabricate the La0.7Sr0.3MnO3-SrRuO3 interface with controlled termination. Ultra-strong antiferromagnetic coupling between the ferromagnets occurs at the MnO2-SrO interface, but not for the other termination, in agreement with density functional calculations. X-ray magnetic circular dichroism measurements reveal coupled reversal of Mn and Ru magnetic moments at the MnO2-SrO interface. Our results demonstrate termination control of magnetic coupling across a complex oxide interface and provide a pathway for theoretical and experimental explorations of novel electronic interface states with engineered magnetic properties.

We investigated \LAO\ - \STO\ heterointerfaces grown either in oxygen rich or poor atmosphere by soft x-ray spectroscopy. Resonant photoemission across the Ti L$_{2,3}$ absorption edge of the valence band and Ti 2p core level spectroscopy directly monitor the impact of oxygen treatment upon the electronic structure. Two types of Ti$^{3+}$ related charge carriers are identified. One is located at the Fermi energy and related to the filling of the \STO\ conduction band. It appears for low oxygen pressure only. The other one is centered at E$_{B}$ $\approx$ 1 eV and independent of the oxygen pressure during growth. It is probably due to defects. The magnitude of both excitations is comparable. It is shown that low oxygen pressure is detrimental for the Ti - O bonding. Our results shed light on the nature of the charge carriers in the vicinity of the \LAO\ - \STO\ interface., Comment: 8 pages, 6 figures

We study the effect of elastic anisotropic biaxial strain on the light emitted by neutral excitons confined in different kinds of semiconductor quantum dots (QDs). We find that the light polarization rotates by up to 80 degree and the excitonic fine structure splitting varies by several tens of $\mu$eVs as the strain is varied. By means of a continuum model we mainly ascribe the observed effects to substantial changes of the hole wave function. These results show that strain-fields of a few permill magnitude are suffcient to dramatically modify the electronic structure of QDs., Comment: Submitted to Phys. Rev. Lett. 4 Pages, 3 figures, Suppl. material not submitted

We investigate the low-temperature electron, lattice, and spin dynamics of LaMnO_3 (LMO) and La_0.7Ca_0.3MnO_3 (LCMO) by resonant pump-probe reflectance spectroscopy. Probing the high-spin d-d transition as a function of time delay and probe energy, we compare the responses of the Mott insulator and the double-exchange metal to the photoexcitation. Attempts have previously been made to describe the sub-picosecond dynamics of CMR manganites in terms of a phenomenological three temperature model describing the energy transfer between the electron, lattice and spin subsystems followed by a comparatively slow exponential decay back to the ground state. However, conflicting results have been reported. Here we first show clear evidence of an additional component in the long term relaxation due to film-to-substrate heat diffusion and then develop a modified three temperature model that gives a consistent account for this feature. We confirm our interpretation by using it to deduce the bandgap in LMO. In addition we also model the non-thermal sub-picosecond dynamics, giving a full account of all observed transient features both in the insulating LMO and the metallic LCMO., Comment: 6 pages, 5 figures http://link.aps.org/doi/10.1103/PhysRevB.81.064434 v2: Abstract corrected

We investigate the structure and magnetic properties of thin films of the LaCoO$_{3}$ compound. Thin films are deposited by pulsed laser deposition on various substrates in order to tune the strain from compressive to tensile. Single-phase (001) oriented LaCoO$_{3}$ layers were grown on all substrates despite large misfits. The tetragonal distortion of the films covers a wide range from -2% to 2.8%. Our LaCoO$_{3}$ films are ferromagnetic with Curie temperature around 85 K, contrary to the bulk. The total magnetic moment is below $1\mu_{B}$/Co$^{3+}$, a value relatively small for an exited spin-state of the Co$^{3+}$ ions, but comparable to values reported in literature. A correlation of strain states and magnetic moment of Co$^{3+}$ ions in LaCoO$_{3}$ thin films is observed., Comment: submitted tu European Phys. J. B

The magnetization of ferromagnetic LaCoO3 films grown epitaxially on piezoelectric substrates has been found to systematically decrease with the reduction of tensile strain. The magnetization change induced by the reversible strain variation reveals an increase of the Co magnetic moment with tensile strain. The biaxial strain dependence of the Curie temperature is estimated to be below 4K/% in the as-grown tensile strain state of our films. This is in agreement with results from statically strained films on various substrates.

We report on the observation of a strain-induced insulator state in ferromagnetic La_0.7Sr_0.3CoO_3 films. Tensile strain above 1% is found to enhance the resistivity by several orders of magnitude. Reversible strain of 0.15% applied using a piezoelectric substrate triggers huge resistance modulations, including a change by a factor of 10 in the paramagnetic regime at 300 K. However, below the ferromagnetic ordering temperature, the magnetization data indicate weak dependence on strain for the spin state of the Co ions. We interpret the changes observed in the transport properties in terms of a strain-induced splitting of the Co e_g levels and reduced double exchange, combined with a percolation-type conduction in an electronic cluster state.

The electronic response of doped manganites at the transition from the paramagnetic insulating to the ferromagnetic metallic state in $\rm La_{1-x}Ca_{x}MnO_3$ for $\rm (x=0.3,0.2)$ was investigated by dc conductivity, ellipsometry, and VUV reflectance for energies between 0 and 24 eV. A stablized Kramers-Kronig transformation yields the optical conductivity and reveals changes in the optical spectral weight up to 24 eV at the metal to insulator transition. In the observed energy range, the spectral weight is conserved within $\rm 0.3 %$. The redistribution of spectral weight between low and high energies has important ramifications for the down-folding of low-energy Hamiltonians. We discuss the importance of the charge-transfer, Coulomb onsite, Jahn-Teller, and screening effects to the electronic structure., Comment: 4 pages, 3 figures

The critical properties at the ferromagnetic - paramagnetic transition have been analysed from data of static magnetization measurements on single crystals of Pr1-xPbxMnO3, for x = 0.23 and x = 0.30. In Pr1-xPbxMnO3 the ferromagnetic ordering and the metal-insulator transition do not coincide in parts of the phase diagram. The crystal with x = 0.23 is a ferromagnetic insulator with Curie temperature Tc = 173 K, while the crystal with x =0.30 has Tc = 198 K and remains metallic up to a metal-insulator transition temperature Tmi = 235 K. The dc magnetization measurements were carried out in the field range from 0 to 5 T for an interval in the critical temperature range Tc+_10 K corresponding to a reduced temperature interval 0.003 < epsilon < 0.6. The exponents beta for spontaneous magnetization, gamma for the initial susceptibility above Tc and delta for the critical magnetization isotherm at Tc were obtained by static scaling analysis from modified Arrott plots and by the Kouvel Fisher method for the insulating crystal with composition x = 0.23. The data are well described by critical exponents similar to those expected for the Heisenberg universality class relevant for conventional isotropic magnets Systematic deviations from scaling in the data for the metallic crystal with composition x = 0.30 are demonstrated from effective critical exponents near the assumed ordering transition. The unconventional magnetic ordering in this system indicates the presence of frustrated magnetic couplings that suppresses magnetic ordering and lowers the transition temperature., Comment: 9 double column pages, 14 figures. 1 table

In this paper, we discuss the most deleterious effect of charge state modification at the Mn site on the ground state of the CMR manganites., Comment: 4 pages; figures are included in the text (ISRS-2004, Chennai, India)

For the first time,we report the effect of pentavalent subtitution at the Mn site of La(0.67)Ca(0.33)MnO(3). The ferromagnetic -metallic ground state modifies to a cluster-glass insulator beyond x=0.03. The observed suppression in the transition temperatures (39K/at.%) is the largest reported for the Mn site subtituted manganites. We argue that charge state(valence) of the substituent has a dominant role in affecting the ferromagnetic - metallic ground state of CMR manganites., Comment: Four pages inclusing three figures.(To appear in J.Magn.Magn.Mater. in 2005)

Results of a study of dc-magnetization M(T, H), performed on a Nd0.6Pb0.4MnO3 single crystal in the temperature range around T_C (Curie temperature) which embraces the critical region | epsilon | = |T -T_C |/T_C <= 0.05 are reported. The magnetic data analyzed in the critical region using the Kouvel-Fisher method give the values for the T_C =156.47 +/- 0.06 K and the critical exponents, beta = 0.374 +/- 0.006 (from the temperature dependence of magnetization), and gamma = 1.329 +/- 0.003 (from the temperature dependence of initial susceptibility). The critical isotherm M(T_C, H) gives delta = 4.547 +/- 0.1. Thus the scaling law gamma+beta=delta beta is fulfilled. The critical exponents obey the single scaling-equation of state M(H, epsilon) = epsilon^b f_+/- (H/epsilon^(beta + gamma)) where, f_+ for T > T_C and f_- for T< T_C. The exponent values are very close to those expected for the universality class of 3D Heisenberg ferromagnets with short-range interactions., Comment: 19 pages, including 6 figures

We report the magnetotransport characteristics of a trilayer ferromagnetic tunnel junction build of an electron doped manganite (La_0.7Ce_0.3MnO_3) and a hole doped manganite (La_0.7Ca_0.3MnO_3). At low temperatures the junction exhibits a large positive tunneling magnetoresistance (TMR), irrespective of the bias voltage. At intermediate temperatures below T_C the sign of the TMR is dependent on the bias voltage across the junction. The magnetoresistive characteristics of the junction strongly suggest that La_0.7Ce_0.3MnO_3 is a minority spin carrier ferromagnet with a high degree of spin polarization, i.e. a transport half metal., Comment: 4 pages, 3 figures, 2nd revised version

We report on the non-linear in-plane electrical transport in coherently grown [La0.7Sr0.3MnO3/SrTiO3] multilayers with ultrathin (< 3 nm) single layers. Current-induced switching of the conductance, with low conductance at larger currents, is demonstrated. The conductance switching is modified under a magnetic field, resulting in an extremely large magnetoresistance of negative, or in a special case even positive, sign. Our results suggest a percolative nature of transport where a large local current density gives rise to a spin-polarizing and a thermal effect of current., Comment: 10 pages, 6 figures