La0.67Ca0.33MnO3 Layer Research Articles

Crossover from magnetostatic to exchange coupling in La0.67Ca0.33MnO3/YBa2Cu3O7/La0.67Ca0.33MnO3 heterostructures

The influence of YBa2Cu3O7 (YBCO) superconductor layer (S-layer) with a varying thickness dYBCO = 20–50 nm on the magnetic coupling between two La0.67Ca0.33MnO3 (LCMO) ferromagnet layers (F-layer, thickness dLCMO = 50 nm) in F/S/F heterostructures (HSs) was investigated by measuring global magnetization (M) in a temperature (T) range = 2–300 K and a magnetic field (H) range = 0–10 kOe. All the HSs were superconducting with the critical temperature (TC) decreasing from = 78 to 36 K with decrease in dYBCO, whereas the ferromagnetic ordering temperature TM = 250 K did not change much. Systematically measured M-H loops of all HSs at both T > TC and T < TC show three main results (a) the two step magnetic reversal above TC converts into a four step reversal below TC in HSs with dYBCO ⩾ 30 nm, (b) the magnitude and magnetic field corresponding to the additional two switching steps show characteristic evolution with T and dYBCO; and (c) the HS with dYBCO = 20 nm shows radically different behaviour, where the two step magnetic reversal above TC continues to persist below TC and converts into a single step reversal at T TC. The first two results indicate magnetostatic coupling between the magnetic domains and the vortices across the two F/S interfaces resulting in reversal dynamics different from that deep within the LCMO layers. Whereas, the result ‘c’ reveals indirect exchange coupling between LCMO layers through the superconducting YBCO layer, which is a clear experimental evidence of coexistence of ferromagnetism and superconductivity in nm scale F/S/F HSs expected theoretically by Sa de Melo (2003 Physica C 387 17–25).

Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures.

The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.

Exchange bias effect in epitaxial La0.67Ca0.33MnO3/SrMnO3 thin film structure

Bilayers consisting of La0.67Ca0.33MnO3 (LCMO) and SrMnO3 (SMO) have been prepared by pulsed-laser deposition on SrTiO3 (001) substrates. Unconventional magnetic coupling was found after cooling in a small field. The LCMO/SMO bilayers exhibit an exchange bias field of 209 Oe, which vanishes as the temperature rises above 90 K. A small magnetization has been found above the Curie temperature of the pure LCMO thin films. Spin-cluster-like antiferromagnetic (AFM)/ferromagnetic (FM) clusters have been deduced to exist at the interface due to the competing types of magnetic order at the interface. The magnetic relaxation is found to follow a double-exponential equation and a slow relaxation process is observed due to the strong exchange coupling between AFM/FM clusters and the LCMO layer. We speculate that the short-range high-temperature FM order of the Mn3+ and Mn4+ moments above the Curie temperature at the interface gives rise to the magnetic regions that pin the FM LCMO layer as the temperature decreases.

Contrasting size-scaling behavior of ferromagnetism in La0.67Ca0.33MnO3 films and La0.67Ca0.33MnO3/CaRuO3 multilayers

Using La0.67Ca0.33MnO3 (LCMO) and CaRuO3 (CRO) as components, the single-layer films, bilayers, trilayers, and superlattices were fabricated on NdGaO3 (110) substrates. These epitaxial structures show quite different Curie temperature (TC) depending on the LCMO layer thickness (x), especially in the low x region. For LCMO films, TC dramatically decreases with x and disappears below 3.2 nm, as previously reported. For LCMO/CRO (CRO/LCMO) bilayers, however, a smooth decline of TC was observed, retaining a TC near 50 K at 1.6 nm. More strikingly, for the multilayers with LCMO sandwiched between CRO, TC is stabilized at ∼250 K even at x of 1.6 nm, before decreasing to 200 K at 0.8 nm. We ascribed these distinct behaviors to the LCMO/CRO interfaces, and a possible charge transfer from CRO to LCMO was suggested to play a vital role in stabilizing the ferromagnetism in ultrathin LCMO. This finding would shed some lights on the dead layer formation in ultrathin manganites and be significant in improving the performance of the related spintronic devices.

Resistance switching behaviors of V-doped La0.67Ca0.33MnO3 thin films on F-doped SnO2 conducting glass

V-doped La0.67Ca0.33MnO3 (LCMO) thin films were prepared on fluorine-doped SnO2 (FTO) conducting glass substrates with a sol-gel technique. The resistance switching properties of Au/V:LCMO/FTO heterostructures investigated by electrochemical workstation showed reproducible resistive switching behaviors at room temperature. The interactions between nonlattice (mobile) oxygen and oxygen vacancies and/or the cationic vacancies contributed to the carrier transport of the LCMO layer sandwiched systems. With proper doping concentration (3% V-doped LCMO), the resistive switching behaviors could be well improved and stabilized. The maximum resistance ratio obtained could be reached up to 700%. The experimental results show a high potential for nonvolatile memory application on amorphous substrates.

Magnetotransport properties of La 0.67 Ca 0.33 MnO 3 /La 0.67 Sr 0.33 MnO 3 bilayers

The perovskite bilayers La0.67Ca0.33MnO3 (LCMO) (1.00 nm) / La0.67Sr0.33MnO3(LSMO) (100 nm) and LSMO (100 nm) / LCMO (100 nm) are fabricated by a facing-target sputtering technique. Their transport and magnetic properties are investigated. It is found that the transport properties between them are different obviously due to distinguishable structures, and the different lattice strains in both films result in the difference of metal-to-insulator transition. Only single-step magnetization loop appears in our bilayers from 5K to 320K, and the coercive force of LSMO/LCMO varies irregularly with a minimum similar to 2387A/m which is lower than that of LCMO and LSMO single layer films. The behaviour is explained by some magnetic coupling.

Transport Properties in YBa&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;8&lt;/sub&gt;/La&lt;sub&gt;0.67&lt;/sub&gt;Ca&lt;sub&gt;0.33&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; Multilayers

Transport properties of YBa2Cu4O8 (YBCO)/La0.67Ca0.33MnO3 (LCMO) multilayers were studied. The metal-semiconductor transition temperature shows an oscillatory behavior with a period ~ 12 nm. In contrast to that for LCMO films, the magnetoresistance ratio for multilayers is enhanced and strongly depends on the thickness of the YBCO layer. These results imply that the magnetic spin interaction between the LCMO layers may exist through the normal-conductive YBCO layer.