NMR investigation of the rare earth pyrochlore Yb₂Pt₂O₇

Until recently, there have been few NMR experiments on the pyrochlores, as many of the well-studied ones (such as Yb₂Ge₂O₇, Dy₂Ti₂O₇ and Yb₂Mo₂O₇ etc.) contain atoms whose nuclei are not suitable for NMR. Recently, however, platinum based pyrochlores have been synthesized. ¹⁹⁵Pt is an excellent nucleus for NMR as it has a large nuclear gyromagnetic ratio, relatively high abundance, and is nuclear spin ½. We present results from a field dependent NMR study of Yb₂Pt₂O₇, from 0.5 T to 8 T. 1/T₁ exponentially decreases as temperature is decreased from ~20 K to ~2 K in 2T and higher. This indicates that the low frequency spin fluctuations freeze out well before the known zero-field transition to a ferromagnet at ~ 0.3 K. Although 1/T₁ continues to decrease with decreasing temperature in the low field cases (1 T and lower), the freezing out of low frequency spin fluctuations is not nearly as dramatic, or definitively exponential, as in the high field case. We attempt to elucidate the behaviour of the low-frequency spin-fluctuations and how they behave with magnetic field.