Large magnetodielectric response of PST/LSMO/LCMO film over a wide temperature range

Pb0.6Sr0.4TiO3/La0.7Sr0.3MnO3/La0.7Ca0.3MnO3 (PST/LSMO/LCMO) film is grown on Si substrate by chemical solution deposition method.

The Surface and Interface Microstructure of Epitaxial Pr0.7Sr0.3MnO3/La0.5Ca0.5MnO3 Bilayer Structure

Epitaxial bilayer structure consisting of ferromagnetic (FM) metallic Pr0.7Sr0.3MnO3 (PSMO) and antiferromagnetic (AFM) insulator La0.5Ca0.5MnO3 (LCMO) was fabricated on (001)-oriented single crystal SrTiO3 (STO) substrate by pulsed laser deposition technique. We studied the surface structure and interdiffusion at interface between PSMO and LCMO by using atomic force microscope and grazing incident x-ray reflectivity (GIXRR). The perfect data fitting result of GIXRR indicated that interdiffusion at the interface of Pr0.7Sr0.3MnO3/La0.5Ca0.5MnO3 (PSMO/LCMO) could not be negligible; there was a large interdiffusion zone at the PSMO/LCMO interfaces with a thickness of about 7 nm. We found that the thickness of the top layer at air/PSMO interface was about 2.5 nm and the mass density of the top layer was about 76.53% of that of PSMO layer. The surface roughness was about 1.6 nm which was consistent with observation by atomic force microscopy. Normal X-ray diffraction (NXRD) was also employed to investigate the average structure. Except from PSMO and LCMO layer diffraction peaks, we observed another additional peak, which was developed from the large disordered layer resulting from interdiffusion at the interface of PSMO/LCMO. This implied that the variation of crystalline structure of PSMO/LCMO film occurred due to interdiffusion. Surface roughness and interdiffusion played an important role in magnetic properties of FM/AFM bilayer.

Observation of Domain Wall Resistance in La0.7Ca0.3MnO3 Films

We report the study of the magnetoresistance (MR) and resistivity as a function of temperature in epitaxial thin films of the La0.67Ca0.33MnO3 type (LCMO). The films deposited onto Y-cut of single-crystalline LiNbO3 (LNO) substrates by pulsed-laser deposition in an on-axis geometry. For comparison, the same manganite film deposited onto LaAlO3 (LAO) substrate is studied. The MR of LCMO/LNO film is found to be anisotropic and exhibits a hysteresis loops in low magnetic fields. When magnetic field is parallel to the film plane a number of jumps are observed in the MR below magnetic fields H~6 kOe. These jumps reflect the presence of pinning centers for domain walls. Evidently, a lattice deformation produced by a mismatch of lattice constants LCMO film and LNO, which lead to distortion of the film, is the origin of such strong pinning centers.

POSSIBLE ABNORMAL MECHANISM FOR LATTICE STRAIN RELAXATION IN La0.7Ca0.3MnO3 THIN FILM

La 0.7 Ca 0.3 MnO 3(LCMO) thin films with the thickness of 50 nm were deposited on (001)-oriented single crystal SrTiO 3(STO), MgO and α- Al 2 O 3(ALO) by 90° off-axis radio frequency magnetron sputtering. Grazing incidence X-ray diffraction technique, associated with normal X-ray diffraction, was performed to measure the in-plane lattice parameter and investigate the lattice strain and strain relaxation in LCMO films. The results indicated that critical thickness of strain relaxation is very small, which may be related to large mismatch between film and substrate. The mechanism for strain relaxation in LCMO film is perhaps different from that for tetragonal distortion.

Colossal Temperature Coefficient of Resistivity in Epitaxial Colossal Magnetoresistive La0.67Ca0.33MnO3 Films

ABSTRACTEpitaxial La0.67Ca0.33MnO3(LCMO) films have been grown by pulsed laser deposition technique on three single crystal substrates: LaAlO3, SrTiO3, and NdGaO3 having lattice mismatch with LCMO film of + 1.26 %, - 0.9 %, and + 0.18 %. We found the transport colossal magnetoresistive (CMR) properties were improved with the reduction of a film/substrate mismatch. Processing conditions for LCMO film on NdGaO3substrate were optimized as well as post-annealing process was employed to achieve a superior temperature coefficient of resistivity TCR = 35 %K−1 and the magnetoresistance MR = 66 % at 7 kOe. To our knowledge, these are the record CMR parameters achieved so far.

Structural Inhomogeneities and Resistivity in Radiation Damaged LA2/3(CA,SR)1/3MNO3-δ Pulsed Laser Deposited Thin Films

ABSTRACTThe relationship between structural distortions and resistivity in pulsed laser deposited La2/3Ca1/3MnO3 (LCMO) and La2/3Ca1/3MnO3 (LSMO) thin films was investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM) and resistivity measurements. The growth defects inherent to annealed films were characterized, and then additional defects were introduced by radiation damage. Epitaxially grown films on (100) LaA1O3 substrates exhibited three primary types of growth defects: interface strain, column boundary mismatch, and column rotation. High resolution TEM measurements show well-ordered regions of film that offer low resistance paths for current flow around growth defects. A series of annealed samples were irradiated with 6 Mev Si+3 ions to produce 0.006 to 0.024 displacements per atom (dpa) in LCMO films, and 0.028 to 0.14 dpa in LSMO films. The peak resistance temperature (Tp) was found to depend strongly on defect concentration, varying from 235K ± 15K for the unirradiated LCMO films to 95K for 0.018 dpa. At 0.024 dpa, the LCMO film was insulating at all temperatures. LSMO films showed a downward shift in Tp from 300K for an unirradiated film to 250K for 0.028 dpa, and complete insulating behavior for 0.14 dpa.

Domain Structure and Colossal Magnetoresistance of La1−xSrxCoO3 and La1−xCaxMnO3

La1−xSrxCoO3 (LSCO) and La1−xCaxMnO3 (LCMO) are a class of magnetic oxides exhibiting the colossal magnetoresistance (CMR) effect. However, the CMR ratio of LSCO is much lower than that of LCMO. Microstructure studies were carried out to understand this difference. In La0.5Sr0.5CoO3 (LSCO), an ordered, anisotropic perovskite-type structure n-LSCO was observed. The ordered structure has a tetragonal cell with a La-Co-Sr-Co- [001] layered atom distribution along the c-axis. This new structure is intrinsic for the LSCO system and is a direct result of the lattice substitution between La and Sr. The entire film is composed of [001], [010] and [100] anisotropic domains with sizes on the order of 30–200 nm. The La0 7Ca0.3MnO3 (LCMO) film, however, does not exhibit a domain structure. It is concluded that the domain structure may have negative effect on the CMR ratio.