Graduation Year

2010

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Physics

Major Professor

Casey W. Miller, Ph.D.

Committee Member

Dale Johnson, Ph.D.

Committee Member

Gerald Woods, Ph.D.

Keywords

Magnetocaloric effect, nanostructuring, magnetic entropy

Abstract

The standard material by which all materials exhibiting magnetocaloric effect are

measured is Gadnolinium. In this work we are attempting to understand how

nanostructuring can impact the magnetocaloric effect, to this end we have grown Gd in

various thin film structures. The samples made were grown via magnetron sputtering on

MgO(100) substrates. Samples of thick Gd (2000 A) were grown and sandwiched

between two layers of Cr or W and annealed at increasing temperatures to study how this

can perturb the magnetic and structural properties of the Gd. Another set of samples was

grown in which Gd (at various thicknesses) is in a multilayer system with W. Here the

purpose is to explore how changing the thickness of the Gd can change its magnetic

properties. Using the appropriate Maxwell relation, the magnetic entropy change was

observed to increase with increasing annealing temperature. In a 0-4T magnetic field

change, the peak entropy was found to go from approximately 1.5 J/kg-K for the

unannealed sample to 4.4 J/kg-K when annealed to 600°C. The multilayers were found

to all have a T

C near 280 K, in contrast with what is predicted by finite size scaling. This

is likely due to pinholes in the W layers allowing the Gd to act as one magnetic material.

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