Manifestation of geometric frustration on magnetic and thermodynamic properties of the pyrochlores Sm2X2O7 (X=Ti,Zr)

Singh, Surjeet and Saha, Surajit and Dhar, SK and Suryanarayanan, R and Sood, AK and Revcolevschi, A (2008) Manifestation of geometric frustration on magnetic and thermodynamic properties of the pyrochlores Sm2X2O7 (X=Ti,Zr). In: Physical Review B: Condensed Matter and Materials Physics, 77 (5).

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Abstract

We present here magnetization, specific heat, and Raman studies on single-crystalline specimens of the first pyrochlore member Sm2Ti2O7 of the rare-earth titanate series. Its analogous compound Sm2Zr2O7 in the rare-earth zirconate series is also investigated in the polycrystalline form. The Sm spins in Sm2Ti2O7 remain unordered down to at least T=0.5 K. The absence of magnetic ordering is attributed to very small values of exchange (θcw∼−0.26 K) and dipolar interaction (μeff∼0.15 μB) between the Sm3+ spins in this pyrochlore. In contrast, the pyrochlore Sm2Zr2O7 is characterized by a relatively large value of Sm-Sm spin exchange (θcw∼−10 K); however, long-range ordering of the Sm3+ spins is not established at least down to T=0.67 K due to frustration of the Sm3+ spins on the pyrochlore lattice. The ground state of Sm3+ ions in both pyrochlores is a well-isolated Kramers doublet. The higher-lying crystal field excitations are observed in the low-frequency region of the Raman spectra of the two compounds recorded at T=10 K. At higher temperatures, the magnetic susceptibility of Sm2Ti2O7 shows a broad maximum at T=140 K, while that of Sm2Zr2O7 changes monotonically. Whereas Sm2Ti2O7 is a promising candidate for investigating spin fluctuations on a frustrated lattice, as indicated by our data, the properties of Sm2Zr2O7 seem to conform to a conventional scenario where geometrical frustration of the spin excludes their long-range ordering.

Item Type:	Journal Article
Publication:	Physical Review B: Condensed Matter and Materials Physics
Publisher:	The American Physical Society
Additional Information:	Copyright of this article belongs to The American Physical Society.
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	24 Mar 2010 10:56
Last Modified:	19 Sep 2010 05:58
URI:	http://eprints.iisc.ac.in/id/eprint/26506

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