Novel Transport Properties in Spatially Confined La0.3Pr0.4Ca0.3MnO3 Thin Films

• Author / Creator

  Jeon, Jaechun

• Novel magneto-transport properties in spatially confined La0.3Pr0.4Ca0.3MnO3 (LPCMO) thin films have been intensively studied in this thesis. Due to the existence of micrometer-scale electronic phase separation in the LPCMO system, it exhibits extraordinary electronic transport behaviour when the lateral dimension of the system is reduced to the size of inherent phase domains. First, we studied the spatial confinement effect on the magnetoresistance in microbridges fabricated from LPCMO thin films. The spatially confined LPCMO micro-bridge was found to produce two maxima in the temperature dependence of the magneto-resistance (MR) as well as in the temperature dependence of the area of the hysteresis loops that exist in an isothermal magnetic field scan of the resistance. One of the peaks is close to the metal-to-insulator transition temperature, as expected for a standard manganite film, while the additional peak occurs at lower temperatures where co-existing metallic and insulating domains have sizes comparable to the spatially confined region. The dependence of the MR of these two peaks on magnetic field is also substantially different, i.e., the MR of the latter peak is considerably less sensitive to magnetic field than the former one. Next, time-dependent measurements of the resistance were carried out on thin films of LPCMO which contain microbridges with lateral dimensions 2 um by 2 um and 25 um by 25um. The 2 um by 2 um microbridge is spatially confined such that at certain temperatures, its lateral dimension is comparable to the sizes of the metallic and insulating domains within the sample. At a fixed temperature, as time increases, sharp jumps in the resistance are observed superimposed upon a long-time evolution of the resistance. The magnitude and sign of these jumps can be controlled by the strength of the magnetic field. By contrast, such resistance jumps are virtually non-existent in the 25 um by 25um microbridge. The results are described within a model of percolation or de-percolation of metallic domains within the confined region of the thin film. We also report the creation of colossal in-plane anisotropic magnetoresistance (CAMR) of > 16,000 % via the engineering of spatial confinement in LPCMO films. Recalling that typical AMR values in films are only a few percent, these results mark an astonishing increase which could shed new light on the nature of the AMR in electronically phase separated confined systems and might potentially lead to fabrication of novel manganite-based switching and sensor devices. The unique colossal behaviour is attributed to the anisotropic percolation of elongated metallic domains whose orientation depends on the direction of the magnetic field as well as the geometry of the micro-system. The effect of the bias current on the in-plane C-AMR was then investigated in spatially confined LPCMO microbridges. Dramatic increases of the C-AMR are found when the bias current is reduced. For example, in one of the samples, the C-AMR changed from ~ 900 % to over ~ 24,000 % as the current is decreased from 1 uA to 10 nA. The results indicate that the bias current can be a useful method to artificially manipulate the C-AMR, via changes in the percolation, in spatially confined manganite thin films. Finally, electron beam induced tunneling magnetoresistance (TMR) behaviour in spatially confined manganite thin films is investigated. Tunneling magnetoresistance (TMR) of ~ 300 % has been produced in spatially confined LPCMO films on LaAlO3 substrates by using electron beam scanning. This new e-beam scanning method to artificially engineer local phase domains can be a powerful tool for fabricating novel manganite-based sensor devices. We believe that the experimental results presented in this thesis will improve the scientific understanding of the electrical properties of these unique systems, i.e. spatially confined electronic phase separated systems, and can also provide important clues on engineering next generation EPS-based applications such as low field magnetoresistance sensor (LF-MR sensors), C-AMR hard disk read head, and magnetoresistive random access memory (M-RAM) devices.

• Subjects / Keywords

  • Manganites

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3639KD12

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.