Volume 85, Issue 8, 15 April 1999
Index of content:
- CMR-THIN FILMS I
85(1999); http://dx.doi.org/10.1063/1.370483View Description Hide Description
We report on a systematic study of the correlation between the disorder produced by ion irradiation and the magnetoresistance (MR) behavior of two doped manganite films: a highly textured film on a (100) substrate and a film of on a YSZ substrate with a high degree of large-angle grain boundary disorder. The films were grown via metal organic chemical vapor deposition and exposed to irradiation of 200 keV Ne ions. The temperature and field dependence of the resistivity were measured on the same samples at different levels of damage. For the Sr-doped film, the bulk magnetic properties were observed to degrade faster with cumulative damage than transport. For both films at low temperature, a low-field hysteretic MR was either induced or enhanced by ion damage. These effects are discussed in terms of diffusive transport through “granular” magnetically disordered regions.
Effects of film thickness and lattice mismatch on strain states and magnetic properties of thin films85(1999); http://dx.doi.org/10.1063/1.370484View Description Hide Description
The effects of strain relaxation on the crystallographic domain structure and on the magnetic and transport properties of epitaxial colossal magnetoresistive (LCMO) thin films have been studied. LCMO films in the thickness range of 100–4000 Å were grown on (001) and (001) substrates, which impose an in-plane tensile and an in-plane compressive biaxial stress in the films, respectively. On (001) substrates, the films can be grown coherently up to a thickness ∼250 Å, then strain relaxation occurs at a thickness of ∼500 Å. In contrast, even the 100 Å filmgrown on (001) is partially relaxed, and the critical thickness for complete strain relaxation is ∼750 Å. The very thin films (<250 Å) show a pure normal orientation for growth on and a pure texture for growth on As thickness increases, the lattice strain relaxes, resulting in mixed and textures for growth on both substrates. Both the Curie and peak resistivity temperatures increase with increasing film thickness, but they do not exhibit a correlation to strain states of the film.
85(1999); http://dx.doi.org/10.1063/1.370485View Description Hide Description
We have performed magnetization and magnetoresistancemeasurements on thin films in order to understand the role of in-plane uniaxial magnetic anisotropy in the magnetoresistance.Transportmeasurements with current flowing along the magnetically easy  and magnetically hard directions exhibit a linear dependence of magnetoresistance on field at high fields due to bulk colossal magnetoresistance. The low field behavior depends not only on the angle of the magnetization with the current but also the direction of the current in the crystal.
85(1999); http://dx.doi.org/10.1063/1.370486View Description Hide Description
We report on the growth of epitaxial thin films on buffered Si(001) substrates. We show that a suitable choice of the buffer heterostructure allows one to obtain epitaxial and (hhh) manganite thin films. The magnetotransport properties are investigated and we have found that the low-field magnetoresistance is directly related to the width of the normal-to-plane rocking curves, irrespective of the film orientation. The magnetic anisotropy of these films has also been determined.
85(1999); http://dx.doi.org/10.1063/1.370487View Description Hide Description
The resistivitytensors of films were investigated at temperatures from the Curie temperature up to 600 K in magnetic fields up to 20 T. The diagonal transport is described by hopping of a small spin polaron cluster of 4 ions to nearest-neighbor spins. A spin-dependent activation energy and a mean field approximation for the magnetization of clustered polaron spins and unclustered Mn ion spins allowed the description of with a minimum of free parameters. The electron-like low field Hall coefficient showed a thermally activated behavior with an activation energy higher than that extracted from diagonal data.