Origin of magnetic freezing in pyrochlore ${\text{Y}}_2{\text{Mo}}_2{\text{O}}_7$

We investigated the nature of the spin-glass like phase transition in the geometrically frustrated pyrochlore lattices ${\text{Y}}_2{\text{Mo}}_2{\text{O}}_7$ using the local probes nuclear and muon magnetic resonances, and the field-dependent long-range probes x-ray and neutron scatterings. The long-range probes indicated that ${\text{Y}}_2{\text{Mo}}_2{\text{O}}_7$ does not undergo any global symmetry changes, even in a field of 6 T. In contrast, the local signal indicates a lattice distortion close to the critical temperature. The nuclei show at least two inequivalent Y sites, and the muons show sublinear line broadening as a function of moment size, over a wide temperature range. The conclusion from all the measurements is that even in high field, the distortion of ${\text{Y}}_2{\text{Mo}}_2{\text{O}}_7$ takes place within the unit cell while its global cubic symmetry is preserved. Moreover, the muon result clearly indicates the presence of magnetoelastic coupling.

Figure 1

(Color online) The raw muon depolarization data taken at $T=24\text{K}$, at two transverse fields. The error bars represent statistical errors. The inset shows the bulk susceptibility $\chi =M/H$ versus temperature in zero-field-cooled and field-cooled conditions taken at a 1 kG field.

Figure 2

(Color online) The TF-$\mu \text{SR}$ relaxation rate, $1/T_2^{\ast }$, versus the magnetization, $M$ at $T=24\text{K}$. The field ${\mu }_{0}H$ is an implicit parameter. Hollow circles are taken from Ref. 10. The red (solid) line is a linear fit to low $M$ data. The black (dotted) line is a fit to $A\cdot M^{\beta }$, where $\beta =0.66\left(12\right)$. The inset shows $1/T_2^{\ast }$ versus $M$ at $T=100\text{K}$.

Figure 3

(Color online) The exponent $\beta$ versus the Temperature. $\beta$ is extracted from $1/T_2^{\ast }$ versus the magnetization $M$ fits to $1/T_2^{\ast }=A{M}^{\beta }$. Line is a guide to the eyes.

Figure 4

(Color online) The NMR spectra at $25\le T\le 300\text{K}$. Inset: the NMR spectrum at $T=25\text{K}$. The line is a fit to a powder spectrum with three sites. The arrows point to the main peak in the powder spectrum of each site.

Figure 5

(Color online) The NMR shift, $K_y$, versus the bulk susceptibility $\chi$ and the temperature as an implicit parameter. In the inset, a theoretical powder spectrum of a nuclear spin 1/2 is depicted.

Figure 6

(Color online) Field and temperature dependence of the (440) Bragg peak from (a) x-ray and (b) neutron scatterings. The error bars representing statistical errors of $\pm 1\sigma$ are smaller than the symbols. The peaks in (a) and (b) are resolution limited.