2007/12/18 by Surjeet Singh, Surajit Saha, S. K. Dhar +4
Chemistry · Materials Science · Physics and Astronomy · #Advanced Condensed Matter Physics #Antiferromagnetism #Chemistry #Condensed matter physics #Crystallography #Frustration #Magnetic field #Magnetization #Multiferroics and related materials #Nuclear materials and radiation effects #Phase (matter) #Physics #Pyrochlore #Quantum mechanics #Spins #cond-mat.mtrl-sci
paper · pdf · doi:10.1103/physrevb.77.054408
24 pages, 6 figures, Accepted for publication in Phys. Rev. B
arxiv created 2007/12/18 · openalex publication_date 2008/02/07 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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\phantom\rule0.3em0exK. The absence of magnetic ordering is attributed to very small values of exchange (\ensuremathθcw\ensuremath∼\ensuremath-0.26\phantom\rule0.3em0exK) and dipolar interaction (\ensuremathμeff\ensuremath∼0.15\phantom\rule0.3em0ex\ensuremathμB) between the Sm3+ spins in this pyrochlore. In contrast, the pyrochlore Sm2Zr2O7 is characterized by a relatively large value of Sm-Sm spin exchange (\ensuremathθcw\ensuremath∼\ensuremath-10\phantom\rule0.3em0exK); however, long-range ordering of the Sm3+ spins is not established at least down to T=0.67\phantom\rule0.3em0exK 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\phantom\rule0.3em0exK. At higher temperatures, the magnetic susceptibility of Sm2Ti2O7 shows a broad maximum at T=140\phantom\rule0.3em0exK, 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.