Percolative transport in the vicinity of charge-order ferromagnetic transition in a hole-doped manganite

We report measurements of non-linear charge transport in epitaxial (La1-x Pr x )0.7Ca0.3MnO3 thin films fabricated on (100) oriented SrTiO3 single crystals by pulsed laser deposition. The end members of this series, namely Pr0.7Ca0.3MnO3 and La0.7Ca0.3MnO3 are canonical charge-ordered (CO) and ferromagnetic manganites, respectively. The onset of the CO state in Pr0.7Ca0.3MnO3 is manifested by a pronounced insulating behavior below ~ 200 K. The CO state remains stable even when a large (~ 2×105 V/cm) electric field is applied across the thin film samples. However, on substitution of Pr with La, a crossover from the highly resistive CO state to a state of metallic character is observed at relatively low electric fields. The current-voltage characteristics of the samples at low temperatures show hysteretic and history dependent effects. The electric field driven charge transport in the system is modelled on the basis of an inhomogeneous medium consisting of ferromagnetic metallic clusters dispersed in a CO background

Growth of [110] La2/3_{2 / 3}Sr1/3_{1 / 3}MnO3_{3} - YBa2_{2}Cu3_{3}O7_{7} heterostructures

YBa$_{2}$Cu$_{3}$O$_{7}$ - La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ heterostructures of [110] orientation are grown to allow direct injection of spin polarized holes from the La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ into the CuO$_2$ superconducting planes. The magnetic response of the structure at T $<$ T$_{sc}$ shows both diamagnetic and ferromagnetic moments with [001] direction as magnetic easy axis. While the superconducting transition temperature (T$_{sc}$) of these structures is sharp ($\Delta$T$_{sc} \simeq$ 2.5 K), the critical current density (J$_c$) follows a dependence of the type $J_c = J{_o}(1-\frac{T}{T_{sc}})^{3/2}$ with highly suppressed J$_o$ ($\simeq 2 \times 10^4$ A/cm$^2$) indicating strong pair breaking effects of the ferromagnetic boundary.Comment: 12 pages five figure

Giant quenching and mobile carrier assisted recovery of ordered moments in La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB>/Er<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB> and La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB>/LaNiO<SUB>3</SUB> superlattices

We report measurements of magnetic ordering temperature, magnetic moment, and resistivity of La0.7Ca0.3MnO3/LaNiO3 and La0.7Ca0.3MnO3/Er0.7Sr0.3MnO3, thin film superlattices. The ordered moment per Mn ion of the ferromagnetic layers undergoes a giant quenching as the insulating spacer layer (Er0.7Sr0.3MnO3) thickness is increased. We attribute the quenching to random pinning of the t2g spins of Mn ions in a disordered interfacial zone of length scale λ c. The nonzero quenching followed by full recovery seen at large n in superlattices with the metallic spacer (LaNiO3), suggest a mobile-carrier-assisted depinning of the t2g spins in the disordered zone

Interfacial Antiferromagnetic Coupling and Dual-Exchange Bias in Tetragonal SrRuO 3 –PrMnO 3 Superlattices

International audienc

Interfacial Antiferromagnetic Coupling and Dual-Exchange Bias in Tetragonal SrRuO 3 –PrMnO 3 Superlattices

International audienceThe functional properties of oxide heterostructures depend on the interfaces accommodating ions, their spins, and structural mismatches. Here, by stabilizing tetragonal symmetry, we achieve the in-plane antiferromagnetic (AFM) ordering and dual-exchange bias in the superlattices consisting of two ferromagnets SrRuO3 (SRO) and PrMnO3 (PMO). The tetragonal symmetry of this superlattice system achieved after the octahedral rotations yield an elongation of the c-axis parameter with Ru–O–Mn bond angle close to 180°, induces an interfacial antiferromagnetic ordering, which is suppressed as the ferromagnetic (FM) ordering in the PMO layer increases. The 0.1 T in-plane cooling field (Hcool) leads to the shift (ca. −0.04 T) of minor hysteresis loop along the negative field axis due to the presence of −0.87 erg/cm2 AFM interfacial exchange coupling energy density (ERu,Mn) at 20 K. The exchange bias field (HEB) switches from negative to positive value with the increase in Hcool. For 5 T Hcool, the HEB is positive, but the ERu,Mn is −1.25 erg/cm2 for n ≤ 8 (n = number of unit cells of PMO) and 1.52 erg/cm2 for n ≥ 8. The HEB and its switching from negative to positive with the increase in Hcool are explained by the interplay of strong antiferromagnetic coupling energy and Zeeman energy at the interfaces. The results demonstrate that the SRO–PMO superlattice could be a model system for the investigation of the interfacial exchange coupling in functional oxides

Ultrathin Scale Tailoring of Anisotropic Magnetic Coupling and Anomalous Magnetoresistance in SrRuO 3 −PrMnO 3 Superlattices

International audienceA strong perpendicular magnetocrystalline anisotropy (PMA) in antiferromagnetically coupled SrRuO3(17 uc (unit cell))/PrMnO3(n uc) superlattices effectively reconstructs the interfacial spin ordering. The occurrence of significant anisotropic interfacial antiferromagnetic coupling between the Ru and Mn ions is systematically tuned by varying the PrMnO3 layer thickness in ultrathin scale from 3 to 12 uc, which is associated with a rise in PMA energy from 0.28 × 106 to 1.60 × 106 erg/cm3. The analysis using the Stoner–Wohlfarth model and density functional theory confirm that the exchange anisotropy is the major contribution to the PMA. The superlattices with PrMnO3 layer thickness ≥7 uc exhibit the tunneling-like transport of Ru 4d electrons, which is rather expected in the stronger antiferromagnetically coupled superlattices with thinner PrMnO3 layer. Tunneling-like transport at thicker spacer layer in the SrRuO3–PrMnO3 superlattice system is an unique feature of two ferromagnet-based superlattices. Our investigations show that the technologically important interfacial magnetic coupling, PMA, and tunneling magnetoresistance could be achieved in a periodically stacked bilayer and can be precisely manipulated by the size effect in ultrathin scale

Ultrathin Scale Tailoring of Anisotropic Magnetic Coupling and Anomalous Magnetoresistance in SrRuO 3 −PrMnO 3 Superlattices

International audienceA strong perpendicular magnetocrystalline anisotropy (PMA) in antiferromagnetically coupled SrRuO3(17 uc (unit cell))/PrMnO3(n uc) superlattices effectively reconstructs the interfacial spin ordering. The occurrence of significant anisotropic interfacial antiferromagnetic coupling between the Ru and Mn ions is systematically tuned by varying the PrMnO3 layer thickness in ultrathin scale from 3 to 12 uc, which is associated with a rise in PMA energy from 0.28 × 106 to 1.60 × 106 erg/cm3. The analysis using the Stoner–Wohlfarth model and density functional theory confirm that the exchange anisotropy is the major contribution to the PMA. The superlattices with PrMnO3 layer thickness ≥7 uc exhibit the tunneling-like transport of Ru 4d electrons, which is rather expected in the stronger antiferromagnetically coupled superlattices with thinner PrMnO3 layer. Tunneling-like transport at thicker spacer layer in the SrRuO3–PrMnO3 superlattice system is an unique feature of two ferromagnet-based superlattices. Our investigations show that the technologically important interfacial magnetic coupling, PMA, and tunneling magnetoresistance could be achieved in a periodically stacked bilayer and can be precisely manipulated by the size effect in ultrathin scale

Effect of Symmetry Breaking on Interlayer Exchange Coupling and Electrical Conduction in SrRuO 3 -PrMnO 3 Superlattices

International audienceThe breaking of orthorhombic to tetragonal crystal symmetry is realizedby increasing the PrMnO3 layer thickness in the superlattices consistingtwo ferromagnets, SrRuO3 and PrMnO3. The octahedral rotation patternis a+c−c− and a0a0c− type for the superlattices with orthorhombic andtetragonal phase, respectively, inferred in the simulated projected densityof states. The 15% reduction in dz2 orbital occupancy due to the a0a0c−type octahedral rotation compared to that of the a+c−c− type suggeststhe presence of stronger antiferromagnetic (AFM) coupling. The largerorbital overlapping leads to a stronger spin–orbit coupling, associatedwith a shift of 42.8% of the minor in-plane field cooled (FC) magnetichysteresis loop(M(H)) along the magnetization axis in orthorhombicsuperlattices. While, minor in-plane FC M(H) shifts along the field axis dueto the strong AFM coupling in tetragonal superlattices. In field-dependentmagnetoresistance, the rotation of spins in the antiferromagneticallycoupled interfacial layers is detected as a unique anomaly, which is strongerin the superlattices for the biased spins and tetragonal symmetry than thepinned spins and orthorhombic symmetry. The results demonstrate thatthe tuning of interfacial exchange coupling and spin-dependent transportby controlling structural distortion could be used as a tool in fabricatingmodern spintronics-based devices

Evidence of weak antilocalization in quantum interference effects of (001) oriented La 0.7 Sr 0.3 MnO 3 –SrRuO 3 superlattices

International audienceQuantum corrections to conductivity in the ferromagnetic La0.7Sr0.3MnO3 (LSMO) and SrRuO3 (SRO) thin films depend on the structural mismatches and interfaces accommodating ions and their spins. Here, by making interfaces of LSMO and SRO in the form of artificial superlattices, we achieve positive magnetoresistance (MR) and weak antilocalization (WAL), although the individual component shows negative MR and weak localization (WL). The [20 unit cell (u.c.) LSMO/3 u.c. SRO]×15 superlattice stabilizes in tetragonal symmetry associated with the rhombohedral and orthorhombic structures and demonstrates the occurrence of the single magnon scattering process. The low-field MR of the superlattice fit to the Hikami–Larkin–Nagaoka expression yields 595 Å phase coherence length (lϕ) with WAL of carriers. As the SRO layer thickness in the superlattice increases to 5 u.c., the value of lϕ = 292 Å decreases, and positive MR increases confirm the manifestation of WAL by SRO. The orthorhombic symmetry of the SRO is preserved in the [20 u.c. SRO/3 u.c. LSMO]×15 superlattice, which shows the existence of locally cooperative bond-length fluctuations and conduction due to the scattering of the electron by the Fermi liquid electrons, bond length, and spin fluctuations. However, as the LSMO layer thickness in the superlattice is increased to 5 u.c., the WL effect suppresses WAL at the low field. The spin–orbit coupling associated with magnetic anisotropy, i.e., spin and bond length fluctuations, modifies the WL in the superlattices and leads to WAL, thereby achieving positive MR

Evidence of weak antilocalization in quantum interference effects of (001) oriented La 0.7 Sr 0.3 MnO 3 –SrRuO 3 superlattices

International audienceThis paper was selected as an Editor's Pick ARTICLES YOU MAY BE INTERESTED IN Emergent ferromagnetism with tunable perpendicular magnetic anisotropy in short-periodic SrIrO 3 /SrRuO 3 superlattice