Two dimensional Langmuir-Blodgett magnets

Abstract

The susceptibility of quasi-two-dimensional magnets formed by the Langmuir-Blodgett deposition of manganese stearate on aluminium foil has been measured at several points between 20 K and 0.4 K. Large area samples of 101 and 11 layers were detected by a SQUID magnetometer. With the magnetic field parallel to the film we deduced an equivalent volume susceptibility of 6.4x10^-3 at 4.2 K. The signals from the multilayers were paramagnetic in nature and no evidence for a transition was found. Unfortunately the signal from a bilayer and monolayer were masked by contaminants on the substrate.

The magnetometer used a cold finger to which the sample was attached. This was then moved into the pick-up coil, which was a second order gradiometer capable of cancelling out the signal from the long (150 mm) substrates. The magnetometer was usefully capable of detecting a sample with a moment down to 5x10^-11 Am² but vibration noise restricted the magnetic field to below 10 mT,

New equations were developed to describe the magnetic signals from a cylindrical magnetised sample within a superconducting shield. They were developed for use on a micro-computer making it possible to simulate the signal from the sample.

The tt-A curves for Manganese stearate were also studied. The uncertainty in the measurement of tx using filter papers was studied and estimated to be 2%. The manganese stearate was observed to transfer by Y and forced-Z type dipping.

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