Page 46 - ILLS Annual Report 2018

MAGNETISM
Tapan Chatterji. French
ILL, Grenoble
Twitter account: Tapan_Chatterji
‘My field of scientific research is magnetism and superconductivity. To study magnetic and superconducting materials, I use neutron scattering along with other laboratory measurements.’
Hyperfine interaction study
of Sr2-xLaxFeCoO6 for
x = 0, 1 and 2 by high-resolution neutron spectroscopy
Backscattering spectrometer IN16B SPHERES at MLZ, Garching
Double perovskites have been under intense investigation for about a decade or so, by way of ab initio electronic structure calculations and many other condensed-matter experimental methods. They show promise as smart, functional materials for electronic industries.
Here, we studied the magnetic
ground state of these materials by measuring their hyperfine interaction and electronic magnetic fluctuations
with inelastic neutron scattering.
AUTHORS
T. Chatterji and M. Appel (ILL)
M. Zamponi (Jülich Centre for Neutron Science at MLZ, Garching, Germany) H.S. Nair (University of Texas El Paso, USA)
R. Pradheesh, G.R. Haripriya, V. Sankaranarayanan and K. Sethupathi (Indian Institute of Technology Madras, Chennai, India)
ARTICLE FROM
PRB (2018)—doi: 10.1103/PhysRevB 98.094429
REFERENCES
[1] A. Heidemann, Z. Phys. 238 (1970) 208
[2] T. Chatterji, B. Frick, M. Zamponi, M. Appel, H.S. Nair, R. Pradheesh,
G.R. Hariprya, V. Sankaranarayanan and K. Sethupathi, Phys. Rev.
B 98 (2018) 094429
[3] M. Appel and B. Frick, Rev. Sci. Instrum. 88 (2017) 036105
The study of hyperfine interaction by high-resolution neutron spectroscopy has become a well-established technique [1]. However, among scientific communities it remains considerably less well known than nuclear magnetic resonance (NMR), Mössbauer, perturbed angular correlation, etc. In addition,
to date it has mainly been employed for studying long-range magnetically ordered systems and seldom for disordered magnetic systems such as spin glass or the so-called magnetic glasses that are not long-range ordered. Here, we report on detailed, hyperfine interaction studies [2] using high-resolution neutron spectroscopy on three double perovskites, Sr2-xLaxFeCoO6 for x = 0, 1 and 2, with canonical spin-glass, magnetic glass and long-range ordered magnetic ground states, respectively.
These studies were carried out on the backscattering spectrometers IN16B of the Institute Laue-Langevin and the SPHERES of the MLZ in Garching.
Looking at figure 1, we can see the inelastic spectra
of Sr2FeCoO6 and SrLaFeCoO6 at T = 2 K, along with vanadium resolution spectra obtained on IN16B. These spectra are background corrected, summed in the Q range 0.44 < Q < 1.9 Å-1 and normalised to the elastic peak maximum. We can see immediately that the spectrum of the canonical spin-glass compound Sr2FeCoO6 (blue triangles), although broader than the vanadium resolution spectra, shows no clear-cut inelastic peaks in the energy loss and energy gain sides, whereas the spectrum for the so-called magnetic glass compound SrLaFeCoO6 shows clear inelastic peaks on both sides of the central elastic peak.
Presented in figure 2 is the temperature variation of
the inelastic spectra of the magnetic glass compound, SrLaFeCoO6. We note that the inelastic peaks on both sides of the elastic peak move towards the central elastic peak as the temperature increases, finally merging with the central elastic peak at about the spin-freezing temperature Tsf = 90 K.
Our analysis, provided in reference [2], shows the spin-glass compound Sr2FeCoO6 to exhibit similar softening behaviour.
Figure 1
Inelastic spectra of Sr2FeCoO6 and SrLaFeCoO6 at T = 2 K, along with vanadium resolution spectra obtained on IN16B with high signal-to-noise ratio (HSNR) [3]. These spectra are background corrected, summed in the
Q range 0.44 < Q < 1.9 Å-1 and normalised to the elastic peak maximum.
ANNUAL REPORT 2018
-5 0 5 Energy (μeV)
SrLaFeCoO6 T = 2 K
Sr2FeCoO6 T = 2 K
Vanadium
1
0.1
0.01
0.001
intensity scaled to maximum