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Origin of the tetragonal distortion in FePd shape memory alloys

Ingo Opahle ,  Klaus Koepernik ,  Manuel Richter 

Leibniz-Institute for Solid State and Materials Research, P.O.Box 270116, Dresden D-01171, Germany

Abstract
Magnetic shape memory alloys (MSMA) have attracted considerable attention as materials for actuator and sensor applications, due to large magnetically induced strains of up to 10%. A promising MSMA is disordered Fe70Pd30 with an induced strain of about 6% and a relatively high blocking stress of 10 MPa.We have calculated the electronic structure of disordered Fe100-xPdx alloys (15<x<50) in the framework of density functional theory using the full potential local orbital (FPLO) code. Disorder was treated in the coherent potential approximation (CPA). Our calculations show a good agreement with available experimental data on magnetic properties, lattice parameters, and specific heat. The origin of the tetragonal distortion in these completely disordered alloys is found to be a Jahn-Teller like effect, which allows the system to reduce its band energy in a narrow composition range.

On the basis of our results, we discuss the prospects for an optimization of the alloys' properties by adding third elements, including effects on the magneto-crystalline anisotropy energy.

 

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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium E, by Ingo Opahle
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-13 19:37
Revised:   2009-06-07 00:44