Temperature, magnetic field, and pressure dependence of the crystal and magnetic structures of the magnetocaloric compound Mn1.1Fe0.9(P0.8Ge0.2)

D. M. Liu, Q. Z. Huang, M. Yue, J. W. Lynn, L. J. Liu, Y. Chen, Z. H. Wu, and J. X. Zhang
Phys. Rev. B 80, 174415 – Published 17 November 2009

Abstract

Neutron powder-diffraction studies of the crystal and magnetic structures of the magnetocaloric compound Mn1.1Fe0.9(P0.8Ge0.2) have been carried out as a function of temperature, applied magnetic field, and pressure. The data reveal that there is only one transition observed over the entire range of variables explored, which is a combined magnetic and structural transformation between the paramagnetic (PM) and ferromagnetic phases (Tc255K for this composition). The structural part of the transition is associated with an expansion of the hexagonal unit cell in the direction of the a and b axes and a contraction of the c axis as the FM phase is formed, which originates from an increase in the intralayer metal-metal bond distance. The application of pressure is found to have an adverse effect on the formation of the FM phase since pressure opposes the expansion of the lattice and hence decreases Tc. The application of a magnetic field, on the other hand, has the expected effect of enhancing the FM phase and increasing Tc. We find that the substantial range of temperature/field/pressure coexistence of the PM and FM phases observed is due to compositional variations in the sample. In situ high-temperature diffraction measurements were carried out to explore this issue, and reveal a coexisting liquid phase at high temperatures that is the origin of this variation. We show that this range of coexisting phases can be substantially reduced by appropriate heat treatment to improve the sample homogeneity.

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  • Received 27 April 2009

DOI:https://doi.org/10.1103/PhysRevB.80.174415

©2009 American Physical Society

Authors & Affiliations

D. M. Liu1, Q. Z. Huang2, M. Yue1, J. W. Lynn2,*, L. J. Liu1, Y. Chen2,3, Z. H. Wu4, and J. X. Zhang1

  • 1Key Laboratory of Advanced Functional Materials Ministry of Education, Beijing University of Technology, 100 Pingleyuan, Chaoyang District, Beijing 100022, China
  • 2NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
  • 3Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
  • 4Neutron Scattering Laboratory, China Institute of Atomic Energy, P.O. Box 275(30), Beijing 102413, China

  • *Corresponding author; jeff.lynn@nist.gov

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Vol. 80, Iss. 17 — 1 November 2009

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