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Experimental and Theoretical Investigations of the Magnetic Phases of Epitaxially Grown EuSe at Low Fields and Temperatures

Published online by Cambridge University Press:  01 February 2011

K. Rumpf ,
P. Granitzer  and
H. Krenn
K. Rumpf
Affiliation:
Institut für Experimentalphysik, Universität Graz, A-8010 Graz, Austria
P. Granitzer
Affiliation:
Institut für Experimentalphysik, Universität Graz, A-8010 Graz, Austria
H. Krenn
Affiliation:
Institut für Experimentalphysik, Universität Graz, A-8010 Graz, Austria
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Abstract

Due to its metamagnetic behaviour the magnetic phases of EuSe are more complicated than for the other Eu-chalcogenides, e.g. EuTe. At very low temperatures (below 2K) there occurs an additional antiferromagnetic phase. This behaviour cannot be solely explained by exchange interaction of nearest neighbors and next nearest neighbors but requires more information about the NNSSNN, NSNS and NNSNNS spin arrangements. Because the nearest and next nearest neighbour exchange constants are nearly cancelled out, higher order interaction becomes important and the biquadratic exchange has also to be taken into account. Our measurements were carried out on an epitaxial grown 2.5 micrometers EuSe film on BaF2. Three regions predicted in the phase diagram of a EuSe bulk crystal are of special interest. For low temperatures (below 1.8K) and low magnetic fields (below 0.05T) a NSNS antiferromagnetic (type II) phase occurs. For higher temperatures from 1.8K to 4.6K and B = 0.1T to 2.5T a NNSNNS ferrimagnetic order exists whereas for lower magnetic fields a further antiferromagnetic (type I) NNSSNNSS-phase is formed above a temperature of 3.6-3.7K. The experimental data show that bilinear mean field calculations taking into account only nearest (JNN) and next nearest exchange (JNNN) interaction fail on this system. Therefore biquadratic exchange (K) has to be included. We present a 12x12 matrix MFA-formalism to extract the proper exchange parameters, which deviate slightly from the bilinear MFA-approach: JNN = 0.165 K, JNNN = -0.1209 K. The biquadratic exchange constant is taken as K = -0.0458 K. We prove this theoretical implication by testing Arrott plots for a varying slope. We made a fit to the experimental data even beyond MFA by taking the corresponding critical exponents of the Heisenberg model.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 875: Symposium O – Thin Films - Stresses and Mechanical Properties XI , 2005 , O4.14
Copyright
Copyright © Materials Research Society 2005

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