LCMO Films Research Articles

Low temperature processing of epitaxial La 1− xCa xMnO 3 thin films by pulsed laser deposition

Magnetoresistive perovskite-like La 0.7Ca 0.3MnO 3 (LCMO) thin films have been successfully grown on (100)LaAlO 3 (LAO) at a relatively low substrate temperature of 600°C–750°C by pulsed laser deposition (PLD) method. Epitaxial LCMO films are obtained at deposition temperature of 650°C or above without post-annealing. The as-deposited films grown at higher substrate temperatures showed lower resistance and higher semiconductor-to-metal transition temperature. For films post-annealed for 1 h at their respective deposition temperatures, a large reduction in their electrical resistivity and an up-shifting of their transition temperature were observed. The maximum magnetoresistance ratio (MR), − Δ R(1 T)/ R(0), for the films deposited and annealed at 650°C and 750°C were 37% and 50%, respectively.

ENHANCED MAGNETORESISTIVE EFFECT IN TRILAYERED FILMS OF LaCaMnO/LaNdCaMnO/LaCaMnO

A series of La0.67Ca0.33MnO3/(La0.35Nd0.65)2/3Ca1/3MnO3/La0.67Ca0.33MnO3(termed as LCMO/LNCMO/LCMO) epitaxial trilayered films, in which LNCMO under zero magnetic field exhibits semiconductor-like conducting behavior down to 4.2K, have been fabricated on SrTiO3(001) substrates by d.c. magnetron sputtering technique. The measurements of resistance show that transport properties of the trilayered films are clearly different from that of the pure LNCMO or LCMO films. In the LCMO(75nm)/LNCMO(450nm)/LCMO(75nm)film, two resistance peaks have been observed. With the measurements of magnetic hysteresis loop, it show that there may exist a magnetic exchange-coupling interaction and an intra-magnetic field in the trilayered film. When the external magnetic field is applied, the resistance decreases and the resistance peak shifts to higher temperature, therefore it appears colossal magnetoresistance effect. Compared with the magnetoresistance response in pure LCMO film, the enhanced magnetoresistance effect have been observed in these trilayed films, and it maintains a stronger magnetoresistance effect in a wide temperature range. We suggest it results from the middle layer LNCMO in the trilayered film.

Structure and Magnetotransport Properties of La2/3Ca1/3MnO3 Thin Films Prepared by Pulsed Laser Deposition

AbstractLa1-xCaxMnO3-δ (LCMO) thin films are grown by pulsed laser deposition on a (100) SrTiO3 substrate at temperatures between 530°C and 890°C. The magnetotransport properties show a high negative magnetoresistance and a shift of the maximum of the R(T) curve as function of temperature. The Curie temperature changes with deposition temperature and film quality in the range of 100-220K. The film quality is characterised by X-ray diffraction and transmission electron microscopy (TEM); film and target compositions were verified by atomic emission spectroscopy. The local structure of the film depends on the growth conditions and substrate temperature. TEM reveals a slight distortion of the film leading to a breakdown of the symmetry from orthorhombic to monoclinic. At the highest growth temperatures, a well defined interface is observed within the LCMO film, parallel to the substrate surface; this interface divides the film into two lamellae with a different microstructure. The lamella close to the substrate is perfectly coherent with the substrate, suggesting that it is strained as a result of the lattice parameter mismatch; the upper lamella shows a typical domain structure with unusual translation interfaces characterised by a displacement vector of the type 1/2 [010]m and 1/2[001]m when referred to the monoclinic lattice.

Discrepancies between infrared and dc resistivities ofLa0.7Ca0.3MnO3samples

Infrared (IR) reflectivity spectra were measured in temperatures between 160 K and 290 K for polycrystalline ${\mathrm{La}}_{0.7}$${\mathrm{Ca}}_{0.3}$${\mathrm{MnO}}_{3}$ (LCMO) samples. Though all the samples showed nearly the same reflectivities, their dc resistivities were varied by more than one order of magnitude. Their resistivities predicted by the Hagen-Rubens relation from the IR spectra were much lower than the values from dc measurements, but they were very close to those of epitaxially grown LCMO films. Our results suggest that dc transport properties of LCMO might be strongly influenced by intergranular resistance, but that the IR responses reflect intrinsic properties of the LCMO grains.

Perovskite oxide superlattices: Magnetotransport and magnetic properties.

We have fabricated perovskite superlattices consisting of two ferromagnetic metallic oxides: ${\mathrm{La}}_{0.67}$${\mathrm{Ca}}_{0.33}$Mn${\mathrm{O}}_{3}$ (LCMO) and SrRu${\mathrm{O}}_{3}$ (SRO). We have investigated the magnetotransport and magnetic properties of a series of samples, in which the layer thickness of LCMO is fixed and that of SRO varied from 0 to 20 unit cells. The magnetoresistance ratio in a superlattice can be increased by a factor of 3 at low temperatures over the MR ratio in pure LCMO film. This substantial enhancement is most likely caused by the interface spin-dependent scattering. The superlattice structure also increases ${T}_{c}$ of LCMO by introducing a biaxial tension, and induces two consecutive switchings of magnetic easy axis direction with increasing SRO thickness.

Giant Magnetoresistance Phenomenon in Laser Ablated La0.6y0.07ca0.33mnox Thin Films

ABSTRACTMicrostructural and magnetoresistance properties of La0.6Y0.07Ca0.33MnOx (Y-doped LCMO) thin films grown in-situ by pulsed laser ablation have been studied. Transmission election microscopy and x-ray diffraction measurements have shown that the Y-doped LCMO thin films grow epitaxially on (100) LaAl03 substrates and are cubic with a lattice parameter of 3.849 ?. The as-deposited films exhibited a metal-insulator transition at 130 K and a giant magnetoresistance (GMR) at 125 K with a MR ratio (dR/RH) of 1500% in the presence of a magnetic field of 6 Tesla. Such a colossal value of MR ratio for as-deposited Y-doped LCMO films is quite promising keeping in view the fact that these films were unannealed and not optimized. We ascribe this magnetoresistance to spin-dependent electron scattering coupled with the presence of intervening O2. ions across Mn3+ and Mn4+ with suppressed separation between Mn-O layers caused by smaller sized Y-dopant. The effect of annealing on the positive-shift of metal-insulator transition temperature and the improvement in GMR ratio has also been discussed. We also report a non-ohmic response in the Y-doped LCMO films which is observed only in the region of the resistance peak and lends support to a conduction mechanism in these materials based on spin-dependent scattering of electrons.

A physical picture for proximity effect coupled to spin fluctuation

Proximity effect between YBCO and a magnetic manganese oxide, La 1−xCa xMnO z (LCMO) or La 1−x Sr xMnO z (LSMO), was investigated through junction characteristics and ferromagnetic resonance (FMR). The experimental study revealed that supercurrents pass through the magnetic material only in the region where the magnetic state changes from ferromagnetism to antiferromagnetism, where spin fluctuation is large. Temperature dependence of g-value was investigated by FMR for LCMO film and YBCO/LCMO/YBCO laminated films. It was shown that itinerancy was maintained at low temperature only for the laminated films. The results suggest that a certain kind of spin interaction, like spin-spin interaction via charge transfer, occurs between the YBCO and the LCMO. A physical picture for proximity effect coupled to spin dynamics is discussed.

Fabrication of YBa2Cu3Oy-La0.7Ca0.3MnOz-YBa2Cu3Oy coplanar junctions and their anisotropic current-voltage characteristics

Two types of YBa2Cu3Oy-La0.7Ca0.3MnOz-YBa2Cu3Oy (YBCO-LCMO-YBCO) coplanar-type junctions with a 0.2 μm gap were fabricated by electron-beam lithography and Ar-ion-beam milling. One is a junction in which a current flows into the a-b plane (ferromagnetic spin arrangement) of the LCMO and then passes through the channel along the c axis (antiferromagnetic arrangement), and the other is a junction in which the current only passes through the a-b plane. In the former junction the current-voltage characteristics show nonlinearity which suggests a superconductive linkage, while the latter has linear characteristics. This anisotropy of the proximity effect is attributed to anisotropy of the spin structure, because the LCMO film has a small anisotropy of the normal decay length in the a-b plane and along the c axis.