Magnetic and crystal field properties of thulium calcium manganite
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Date
2004-02-04
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Institute of Physics
Abstract
For sufficiently large average Ln/A radii, the hole-doped manganites Ln2/3A1/3MnO3 (Ln =
lanthanide, A = divalent metal) exhibit “colossal” magneto-resistance (CMR), which is
associated with a transition from paramagnetic insulator to a low temperature ferromagnetic
metal phase. However, with decreasing radius, the transition temperature is lowered and the
ordered phase eventually reverts to that of a magnetic insulator. In this work, 169Tm
Mössbauer spectroscopy has been used to investigate Tm2/3Ca1/3MnO3, which falls into the
latter category. From the temperature of the onset of line broadening, the magnetic ordering
temperature is determined as Torder ≈ 40 K (compared with ≈ 32 K from a.c. and d.c.
susceptibility). The local Tm3+ magnetisation is almost certainly that of an isolated pseudodoublet
ground state driven by a weak (compared with the crystal field) Mn-Tm exchange
interaction. To a good approximation, the low temperature 169Tm spectrum is the
superposition of a relaxation-broadened sextet and a paramagnetic doublet. This is consistent
with regions of large slowly fluctuating magnetic clusters and regions of smaller rapidly
fluctuating clusters, as has been observed for the generic CMR manganite, La2/3Ca1/3MnO3.
However, recent neutron diffraction measurements performed on the Bragg Institute's HRPD
facility are insensitive to this weak magnetism, suggesting a complex (perhaps spin-glass in
nature) Mn sub-lattice magnetisation. The refinement of the position parameters for the nearneighbour
oxygen atoms has assisted with the interpretation of the temperature-dependent
169Tm quadrupole interaction data in terms of a crystal field scheme for the Tm3+ ion. The
appropriateness of this scheme will be considered in terms of the above observations.
This work was supported by separate grants for source irradiation and neutron diffraction
from the Australian Institute of Nuclear Science and Engineering.
Description
Keywords
Magnetic properties, Crystal structure, Thulium, Rare earths, Calcium, Manganates, Ferromagnetic materials, Spectroscopy, ANSTO, Australia, Spin glass state
Citation
Steward, G. A., Edge, A. V. J., Studer, A., Elcombe, M., Horvat, J., & Lewis, R. (2004). Magnetic and crystal field properties of thulium calcium manganite. Poster presented to the 28th Annual Condensed Matter and Materials Meeting, Charles Sturt University, Wagga Wagga, 3-6 February 2004. Retrieved from: https://www.physics.org.au/wp-content/uploads/cmm/2004/04handbook.pdf