$\mu$SR study of NaCaNi2F7 in zero field and applied longitudinal magnetic field

Rich physics of abundant magnetic ground states has been realized in the A$_2$B$_2$X$_7$ geometrically frustrated magnetic pyrochlores. Recently, a new spin-$1$ Ni$^{2+}$ pyrochlore, NaCaNi$_2$F$_7$, was synthesized and shown to have spin freezing at 3.6~K with a frustration index of $f\sim36$ and antiferromagnetic exchange interactions [1] . This structure has chemical disorder on the A site caused by randomly distributed Ca and Na ions, which causes bond disorder around the magnetic Ni sites. We present Zero Field (ZF) and Longitudinal Field (LF) muon spin rotation ($\mu$SR) measurements on this single crystal pyrochlore. Our data shows that the Ni$^{2+}$ spins start freezing around 4~K giving a static local field of $\sim$140 G. The data show no oscillations down to 75 mK which indicates no long range magnetic order. They are well described by the dynamic Gaussian Kubo-Toyabe function with a non-zero hopping rate that is not easily decoupled with an applied longitudinal field, which implies persistent spin dynamics down to 75 mK.