Experiment-1: Colossal Magneto-Resistive (CMR) effect

(Web site under construction)

Objective: To study the temperature dependence of the magnetoresistance of a LaSrMnO3 thin film.

Theory / Background: The colossal magneto-resistive (CMR) manganites (see Wikipedia) are known for their very large MR near their metal insulator transition. The metal insulator transition also coincides with the magnetic ordering. The detailed physics behind this CMR effect has been puzzling for sometime. The present understanding of these compounds is based on the Zener double exchange mechanism with corrections arising from the electron-lattice interactions. Click here to know more about Magnetoresistance and how it can arise in general.

Principle & Apparatus: We use van der Pauw method for measuring resistivity by four probe method. In this method four contacts are made at the four corners of a rectangular thin film. A known current is passed through two contacts at one edge while the voltage is measured at the opposite contacts.

Method: In the LabView interface the user has two options: 1) Field scan at a fixed temperature 2) Temperature scan at a fixed field. In both cases user has to decide the amount of current for measuring the resistance. In the first case the user has to give fixed temperature while the resistance is measured as a function of the magnetic field in a range decided by the user. In the second one the user has to give a temperature range and the fixed magnetic field value. While the field dependent data are faster the temperature dependence may take more time for stabilizing the temperature. In both the cases the direction of field could be either perpendicular to the film or parallel to it.

Detailed Manual: To be added

Links to Experiments

Internal (inside IITK)

1. Resistance vs Temperature (simulation)

2. Resistance vs Magnetic Field (simulation)

External (outside IITK)

1. Resistance vs Temperature (simulation)

2. Resistance vs Magnetic Field (simulation)