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Magnetic order and spin fluctuations in the spin liquid Tb$\_2$Sn$\_2$O$\_7$

I. Mirebeau·A. Apeteri·J. Rodriguez-Carvajal·P. Bonville·A. Forget·D. Colson·V. Glazkov·J. P. Sanchez·O. Isnard·E. Suard
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Abstract

We have studied the spin liquid Tb$\_2$Sn$\_2$O$\_7$ by neutron diffraction and specific heat measurements. Below about 2 K, the magnetic correlations change from antiferromagnetic to ferromagnetic. Magnetic order settles in two steps, with a smeared transition at 1.3(1) K then an abrupt transition at 0.87(2) K. A new magnetic structure is observed, not predicted by current models, with both ferromagnetic and antiferromagnetic character. It suggests that the spin liquid degeneracy is lifted by dipolar interactions combined with a finite anisotropy along $<111>$ axes. In the ground state, the Tb$^{3+}$ ordered moment is reduced with respect to the free ion moment (9 $μ\_{\rm B}$). The moment value of 3.3(3) $μ\_{\rm B}$ deduced from the specific heat is much smaller than derived from neutron diffraction of 5.9(1) $μ\_{\rm B}$. This difference is interpreted by the persistence of slow collective magnetic fluctuations down to the lowest temperatures.

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I. Mirebeau, A. Apeteri, J. Rodriguez-Carvajal, P. Bonville, A. Forget, D. Colson, V. Glazkov, J. P. Sanchez, O. Isnard, E. Suard. 2005-03-15. Magnetic order and spin fluctuations in the spin liquid Tb$\_2$Sn$\_2$O$\_7$. https://doi.org/10.1103/physrevlett.94.246402

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