M. Rajeswari

Strain-driven charge-ordered state in La 0.67 Ca 0.33 MnO 3

We present evidence for the coexistence of ferromagnetic metallic and charge-ordered insulating phases in strained thin films of

Two-phase behavior in strained thin films of hole-doped manganites

{\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_{3}

Growth of colossal magnetoresistance thin films on silicon

at low temperatures. Such a phase-separated state is confirmed using low-temperature magnetic force microscopy and magnetotransport measurements. This phase separated state is not observed in the bulk form of this compound and is caused by the structural inhomogeneities due to the nonuniform distribution of strain in the film. The strain weakens the low-temperature ferromagnetic metallic state and a charge-ordered insulator is formed at the high strain regions. The slow dynamics of the transport properties of the mixed phase is illustrated by measurements of the long-time scale relaxation of the electrical resistance.

Effects of annealing and strain on La1−xCaxMnO3 thin films: A phase diagram in the ferromagnetic region

We present a study of the effect of biaxial strain on the electrical and magnetic properties of thin films of manganites. We observe that manganite films grown under biaxial compressive strain exhibit island growth morphology which leads to a nonuniform distribution of the strain. Transport and magnetic properties of these films suggest the coexistence of two different phases, a metallic ferromagnet and an insulating antiferromagnet. We suggest that the high strain regions are insulating while the low strain regions are metallic. In such nonuniformly strained samples, we observe a large magnetoresistance and a field-induced insulator-to-metal transition.

Correlation between magnetic homogeneity, oxygen content, and electrical and magnetic properties of perovskite manganite thin films

We are able to grow high quality La0.67Sr0.33MnO3(LSMO) colossal magnetoresistive (CMR) thin films on Y‐stabilized zirconia (YSZ) buffered (100) Si substrates using a Bi4Ti3O12 texturing and lattice matching layer. The CMR films have very high structural perfection and show excellent transport and ferromagnetic properties, including the almost full saturation magnetization values and narrow ferromagnetic resonance peaks (15 Oe at 290 K). The lattice matching template/buffer layer approach is suitable for the high quality CMR films on Si. A close correlation between the magnetic hysteresis loop and the field dependence of MR is observed at lower temperatures.

Pulsed-laser-deposited epitaxial Sr2FeMoO6−y thin films: Positive and negative magnetoresistance regimes

Oriented, single phase thin films of La1−xCaxMnO3 have been deposited onto (100)-oriented LaAlO3 (0.1<x<0.5) substrates using the pulsed laser deposition technique. While for some compositions, the physical properties (transport and magnetization) of the as-grown films are higher than the bulk values, for other calcium contents the optimized properties are obtained only after annealing under oxygen. These data can be partly explained by changes in oxygen content resulting in cationic vacancies, and thus self-doping effects, accompanying structural changes, may be the cause of properties beyond the phase diagram. We propose a phase diagram for (La1−xCax)1−y□yMnO3 (0.1<x<0.5) thin films.

Effect of substrate-induced strain on the charge-ordering transition in Nd0.5Sr0.5MnO3 thin films

Perovskite manganese oxide materials known for the phenomenon of colossal magnetoresistance often exhibit anomalously large 1/f noise and large, temperature-dependent ferromagnetic resonance (FMR) linewidths. We show that in epitaxial films, these anomalies are very sensitive to oxygen partial pressure during film growth and to postdeposition thermal processing in oxygen, suggesting that oxygen stoichiometry plays a key role. We find that the temperature coefficient of resistance (TCR) at the metal–insulator transition increases and the FMR linewidth decreases as we increase the oxygen partial pressure during growth. Postdeposition heat treatment in oxygen leads to further increase in TCR and decrease in FMR linewidth, accompanied by a dramatic reduction in 1/f noise magnitudes.

Low‐frequency optical response in epitaxial thin films of La0.67Ca0.33MnO3 exhibiting colossal magnetoresistance

Epitaxial thin films of ordered double-perovskite Sr2FeMoO6−y are deposited on (001) SrTiO3 substrates by pulsed-laser deposition using a two step growth process. Selection of growth conditions is found to lead to either highly conductive metallic thin films (residual resistivity of about 1 μΩ cm) or semiconducting films. The metallic films show a positive magnetoresistance (MR) as high as 35%, while the semiconducting films show a negative MR of −3%, at a temperature of 5 K and a field of 8 T.

Influence of strain and microstructure on magnetotransport in La0.7Ca0.3MnO3 thin films

We report the synthesis and characterization of Nd0.5Sr0.5MnO3 thin films grown by the pulsed laser deposition technique on [100]-oriented LaAlO3 substrates. X-ray diffraction (XRD) studies show that the films are [101] oriented, with a strained and quasi-relaxed component, the latter increasing with film thickness. We observe that transport properties are strongly dependent on the thickness of the films. Variable temperature XRD down to 100 K suggests that this is caused by substrate-induced strain on the films.

Improved properties of La2/3Ca1/3MnO3 thin films by addition of silver

We report measurements of the low‐frequency optical response in epitaxial thin films of La0.67Ca0.33MnO3 in the temperature range covering both the ferromagnetic metallic state and the paramagnetic insulating state. We observe a bolometric optical response in fully oxygenated films of the above composition as well as in oxygen deficient films. In both types of samples, the optical response is thermal in nature as indicated by its proportionality with the temperature derivative of the resistance dR/dT.