Page 25 - ILL Annual Report 2019

0.1 rGd-Gd
0.0 -0.1 -0.2
a)$ b)$
calc. AIAO
the second lower temperature range is related to the perpendicular component of the magnetic moment,
which presents a tendency to order below 1 K in
another antiferromagnetic pattern called ‘Palmer–Chalker’ (figure 1c). Note that the experiment on D4 allowed us to analyse the diffraction data using magnetic pair distribution function (mPDF) analysis in real space (figure 1e), a promising method for handling ill-ordered magnetic materials.
Finally, we have been able to model and interpret
this peculiar magnetic ground state as well as the associated excitations probed by an inelastic neutron scattering experiment on IN6-SHARP. The key ingredients responsible for the resulting complex antiferromagnetic pattern (figure 1d) are tiny anisotropic terms. The effect of these usually neglected contributions in Gd compounds is actually exacerbated by magnetic frustration in this new member of the pyrochlore family, eventually giving rise to a magnetic moment decoupling mechanism.
10
b–d) Grey lines: Monte Carlo simulations
of equal-time scattering functions using 4 the instrumental Q resolution. The model
takes into account the local field of the Ir,
antiferromagnetic interactions between the 2 Gd magnetic moments and tiny magnetic
anisotropy terms.
d) Red line: FULLPROF refinement of 0 the diffraction pattern, including an
all-in/all-out component of the magnetic
moments and Palmer–Chalker correlations
of the perpendicular component.
5K MCcalc. 8
a) b)6 4 2
8 from D7 polarised neutron measurements at 6
50 mK 600 mK 1.2K
5K
1.0
Figure 2
a–d) Magnetic scattering of Gd2Ir2O7 various temperatures.
MC calc.
Fit
MC calc. 50 mK
8 6 4 2
8 6 4 2 0
0.2 Gd2Ir2O7
e)
0 5 10 15 20
r (Å)
0.5
1.5
2.0
0.5
1.0
2.0
c)
element (red) by the Ir all-in/all-out order (blue).
Scheme of different configurations of the Gd magnetic moment on a tetrahedron:
b) All-in/all-out order of the component of the magnetic moment along the local directions (diagonals) of the tetrahedron.
c) Palmer–Chalker non-collinear antiferromagnetic order of the complementary component in the planes perpendicular to the local directions.
d) Total magnetic moments (black) obtained from the superposition of the two components.
e) mPDF obtained by Fourier transforming the D4 magnetic diffractogram compared with that calculated from an all-in/all-out configuration only. The additional negative peak reveals local antiferromagnetic correlations in Gd2Ir2O7 ascribed to the Palmer–Chalker component.
d)$
a) Sketch of the all-in/all-out ordering produced on the rare-earth
Figure 1
-1 Q (Å )
-1 Q (Å )
1.2 K
c)
d)
1.5
SCIENTIFIC HIGHLIGHTS
22-23
Magnetic scattering (a.u.)
mPDF (Å-2)
Magnetic scattering (a.u.)
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