Neutron diffraction and ESR studies of pseudocubic Nd 0.75Ba 0.25MnO 3 and its unusual critical behavior above T C
Results of structural neutron diffraction study and electron spin resonance (ESR) measurements are presented for insulating Nd 1− x Ba x MnO 3 ( x = 0.25 ) with the Curie temperature T C ≈ 129 K . Its pseudocubic structure reveals the definite distortions to a lower symmetry. Detailed analysis of th...
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Published in | Journal of magnetism and magnetic materials Vol. 300; no. 1; pp. 44 - 47 |
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Main Authors | , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier B.V
2006
|
Subjects | |
Online Access | Get full text |
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Summary: | Results of structural neutron diffraction study and electron spin resonance (ESR) measurements are presented for insulating Nd
1−
x
Ba
x
MnO
3 (
x
=
0.25
) with the Curie temperature
T
C
≈
129
K
. Its pseudocubic structure reveals the definite distortions to a lower symmetry. Detailed analysis of the data is performed in the frame of Pbnm space group in a temperature range 4.2–300
K. The compound is found to exhibit the Jahn-Teller (JT) transition at
T
JT≈250
K. Character of the coherent JT distortions and their temperature evolution differ from those of the
x
=
0.23
manganite. The ESR results correspond to behavior of a 3D isotropic ferromagnet above
T
*
≈
143
K
(
τ
*
≈
0.12
⩽
τ
<
1
,
τ
=
(
T
–
T
C
)
/
T
C
)
. It is shown that an anisotropic exchange coupling of the Mn and Nd magnetic moments may give a substantial contribution in ESR linewidth masking its critical enhancement. The different temperature treatments (slow/fast cooling/heating with/without external magnetic field) of the sample reveal a temperature hysteresis of the ESR spectra below
T* indicating an anomalous response in the paramagnetic region. The study of the magnetic phase transition in the
x
=
0.23
and 0.25 NdBa manganites suggests a change in its character from the second to first order at
T*. The conventional free energy including the magnetization and magnetic field failed to describe this first-order transition. The unconventional critical behavior is attributed to an orbital liquid metallic phase that begins to coexist with the initial orbital-ordered phases below
T*. |
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ISSN: | 0304-8853 |
DOI: | 10.1016/j.jmmm.2005.10.029 |