Page 40 - ILLS Annual Report 2018

MAGNETISM
José Alberto Rodríguez Velamazán.
Spanish. ILL
‘I received my PhD from the University of Zaragoza, Spain, in 2007. I then moved to the ILL, where I have been working as a scientist, first for the Spanish CRGs and then as ILL staff. My main research focus is magnetic materials of molecular base.’
Switching of the chiral
magnetic domains in the hybrid molecular/inorganic multiferroic (ND4)2[FeCl5(D2O)]
Spin-polarised hot-neutron diffractometer D3
Magneto-electric multiferroics are materials that can host electric and magnetic
order simultaneously. A strong coupling between both orders, as achieved in
the so-called spin-driven multiferroics,
leads to remarkable possibilities for cross-control of the physical properties. Important efforts have in recent years
been dedicated to innovative approaches allowing a rational design of such systems. (ND ) [FeCl (D O)] represents a promising
AUTHORS
J.A. Rodríguez-Velamazán, O. Fabelo, J. Rodríguez-Carvajal and N. Qureshi (ILL)
J. Campo (CSIC-University of Zaragoza, Spain)
L.C. Chapon (Diamond light source, Didcot, UK)
ARTICLE FROM
Sci. Rep. (2018)—doi: 10.1038/s41598-018-28883-z (Publication funded through FILL2030 Open Access programme)
REFERENCES
[1] M. Ackermann, D. Brüning, T. Lorenz, P. Becker and L. Bohatý, New J. Phys. 15 (2013) 123001
[2] J.A. Rodríguez-Velamazán, O. Fabelo, A. Millán, J. Campo, R.D. Johnson and L. Chapon, Sci. Rep. 5 (2015) 14475
[3] Y. Tokura, S. Seki and N. Nagaosa, Rep. Prog. Phys. 77
(2014) 076501
[4] N. Qureshi, Mag2Pol. arXiv 1801 (2018) 08431
(ND4)2[FeCl5(D2O)] is a spin-driven multiferroic, with a strong magneto-electric coupling [1] that derives from an incommensurate cycloidal magnetic structure in the ground state (below 6.9 K) [2]. The cycloid propagates along the c-axis with magnetic moments mainly contained in the ac-plane. A ferroelectric polarisation, primarily directed along the a-axis, develops in this phase [1], which is compatible with the spin current mechanism of magneto-electric coupling [3]. The cycloidal spin arrangement implies two ‘chiral’ domains with opposite rotation of the cycloids (figure 1), which directly correspond to electric domains with opposite polarities. Therefore, by applying an E-field, one can manipulate the population of the ‘chiral’ magnetic domains.
We used spherical neutron polarimetry, which is directly sensitive to the absolute magnetic configuration and domain population, to unambiguously prove the multiferroicity of
this material. This technique is ideally suited to studying complex magnetic structures since it allows access to the direction and phase of the magnetic scattering, unreachable by unpolarised methods. For each measured reflection, and in a particular reference frame, we obtain the polarisation matrix P, with matrix elements Pij (i, j = X, Y, Z), representing the polarisation of the scattered beam in the direction j, for
2
4 2 5
example of the new hybrid molecular/
inorganic approach to creating materials with strong magneto-electric coupling.
Figure 1
Schematic representation of the magnetic structure of the two magnetic domains, with the direction of the resulting electric polarisation.
ANNUAL REPORT 2018