Evidence of tetragonal distortion as the origin of the ferromagnetic ground state in $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$ nanoparticles

Evidence of tetragonal distortion as the origin of the ferromagnetic ground state in $γ − Fe$ nanoparticles

V. Augustyns, K. van Stiphout, V. Joly, T. A. L. Lima, G. Lippertz, M. Trekels, E. Menéndez, F. Kremer, U. Wahl, A. R. G. Costa, J. G. Correia, D. Banerjee, H. P. Gunnlaugsson, J. von Bardeleben, I. Vickridge, M. J. Van Bael, J. Hadermann, J. P. Araújo, K. Temst, A. Vantomme, and L. M. C. Pereira

Phys. Rev. B 96, 174410 – Published 7 November 2017

Abstract

$γ − Fe$ and related alloys are model systems of the coupling between structure and magnetism in solids. Since different electronic states (with different volumes and magnetic ordering states) are closely spaced in energy, small perturbations can alter which one is the actual ground state. Here, we demonstrate that the ferromagnetic state of $γ − Fe$ nanoparticles is associated with a tetragonal distortion of the fcc structure. Combining a wide range of complementary experimental techniques, including low-temperature Mössbauer spectroscopy, advanced transmission electron microscopy, and synchrotron radiation techniques, we unambiguously identify the tetragonally distorted ferromagnetic ground state, with lattice parameters $a = 3.76 (2) Å$ and $c = 3.50 (2) Å$ , and a magnetic moment of 2.45(5) $μ_{B}$ per Fe atom. Our findings indicate that the ferromagnetic order in nanostructured $γ − Fe$ is generally associated with a tetragonal distortion. This observation motivates a theoretical reassessment of the electronic structure of $γ − Fe$ taking tetragonal distortion into account.

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Received 9 June 2017
Revised 16 October 2017

DOI:https://doi.org/10.1103/PhysRevB.96.174410

Physics Subject Headings (PhySH)

Crystal structure Nanocrystals

Magnetic nanoparticles

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

V. Augustyns¹, K. van Stiphout¹, V. Joly¹, T. A. L. Lima¹, G. Lippertz¹, M. Trekels¹, E. Menéndez¹, F. Kremer², U. Wahl³, A. R. G. Costa³, J. G. Correia³, D. Banerjee⁴, H. P. Gunnlaugsson¹, J. von Bardeleben⁵, I. Vickridge⁵, M. J. Van Bael⁶, J. Hadermann⁷, J. P. Araújo⁸, K. Temst¹, A. Vantomme¹, and L. M. C. Pereira^1,*

¹KU Leuven, Instituut voor Kern – en Stralingsfysica, 3001 Leuven, Belgium
²Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, ACT 0200, Australia
³Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela, Portugal
⁴Dutch-Belgian Beamline (DUBBLE), ESRF – The European Synchrotron, CS 40220, 38043 Grenoble, France
⁵Institut des Nanosciences de Paris (INSP), Universite Paris 6&7, UMR 7588 au CNRS 140, 75015 Paris, France
⁶KU Leuven, Laboratory of Solid-State Physics and Magnetism, 3001 Leuven, Belgium
⁷Electron Microscopy for Materials Science (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
⁸IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Universidade do Porto, 4169-007 Porto, Portugal

^*lino.pereira@kuleuven.be

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Vol. 96, Iss. 17 — 1 November 2017

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Physical Review B

covering condensed matter and materials physics

Evidence of tetragonal distortion as the origin of the ferromagnetic ground state in $γ − Fe$ nanoparticles

V. Augustyns, K. van Stiphout, V. Joly, T. A. L. Lima, G. Lippertz, M. Trekels, E. Menéndez, F. Kremer, U. Wahl, A. R. G. Costa, J. G. Correia, D. Banerjee, H. P. Gunnlaugsson, J. von Bardeleben, I. Vickridge, M. J. Van Bael, J. Hadermann, J. P. Araújo, K. Temst, A. Vantomme, and L. M. C. Pereira

Phys. Rev. B 96, 174410 – Published 7 November 2017

Abstract

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Physical Review B

covering condensed matter and materials physics

Evidence of tetragonal distortion as the origin of the ferromagnetic ground state in γ−Fe nanoparticles

V. Augustyns, K. van Stiphout, V. Joly, T. A. L. Lima, G. Lippertz, M. Trekels, E. Menéndez, F. Kremer, U. Wahl, A. R. G. Costa, J. G. Correia, D. Banerjee, H. P. Gunnlaugsson, J. von Bardeleben, I. Vickridge, M. J. Van Bael, J. Hadermann, J. P. Araújo, K. Temst, A. Vantomme, and L. M. C. Pereira

Phys. Rev. B 96, 174410 – Published 7 November 2017

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Evidence of tetragonal distortion as the origin of the ferromagnetic ground state in $γ − Fe$ nanoparticles