Structural and magnetic phase separation in PrMn2Ge2-xSix compounds
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Date
2011-02-03
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Institute of Physics
Abstract
Ternary intermetallic compounds of RMn2X2 (where R = rare earth or Yttrium and X = Si or Ge) display a rich variety of magnetic structures due to sharp changes in magnetic exchange interactions between neighbouring manganese atoms, resulting from changes in chemical pressure. Observed variants in the magnetic structure include ferromagnetic (f), collinear & non-collinear antiferromagnetic (a/f), mixed axial f + planar a/f, and even incommensurate a/f structures. This remarkable behaviour is symptomatic of subtle changes in interatomic bond lengths, differentiated at sub-picometre length scales. Transformation between magnetic variants is often accompanied by structural distortions due to magnetoelastic coupling. Further to this, we find that some pseudoternaries, in which one or more sites has mixed occupancy (e.g. La & Y mixed on the R site or Si & Ge mixed on the X site), simultaneously display two structural variants with different axial magnetic order (f or a/f). Such behaviour is most clearly seen in PrMn2Ge2-xSix compounds where x ≈ 1. We report a neutron diffraction study on the PrMn2Ge2-xSix system, through which we gain new insights into the magnetic and structural origins of the curious behaviour of these compounds. In certain regions of the phase diagram we clearly see phase separation (both structural and magnetic), which leads us to propose a two-phase structural model driven by changes in the Mn-Mn magnetic exchange energy, and related to variations in local strain
propagated by the shared crystallographic sites. This interpretation brings into question whether a random substitution could produce such remarkable magnetoelastic phenomena or whether local site-specific atomic order is prevalent in the family of mixed 122 compounds.
Description
Keywords
Praseodymium, Intermetallic compounds, Yttrium, Interactions, Manganese, Atoms, Ferroelectric materials, Antiferromagnetism, Germanium, Silicon, Coupling
Citation
Wang, J. L., Kennedy, S. J., Campbell, S. J., Hofmann, M., Zeng, R., Dou, S. X., Arulraj, A. & Stusser, N. (2011). Structural and magnetic phase separation in PrMn2Ge2-xSix compounds. Paper presented to the Australian and New Zealand Institutes of Physics 35th Annual Condensed Matter and Materials Meeting, Charles Sturt University, Wagga Wagga, NSW, 2nd - 4th February, 2011. Retrieved from: https://physics.org.au/wp-content/uploads/cmm/2011/