Thermomagnetic Studies of K$_{2}$NaCrO$_{8}$*

There has been renewed interest in the search for new model quantum spin systems that can exhibit BEC of magnons. K$_{2}$NaCrO$_{8}$ is one of the simplest spin systems available since $S=\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $ and $I$ = 0. Specific heat ($C_{p})$ measurements indicate that this material orders antiferromagnetically at $T_{N} \quad \sim $ 1.7 K in zero-field [1]. Application of an external magnetic field pushes the $C_{p}$ maximum to lower temperatures. Torque and AC susceptibility measurements show that the transition temperature is rapidly suppressed around 7.4 T, with no hysteretic behavior, implying the presence of a quantum phase transition. Measurements are underway to map the phase boundary in the $T \quad \to $ 0 K, B $\sim $ 7.4 T region and extract the critical exponent ($\alpha )$ from the relation $k_{B}T_{c} \quad \approx $ (B$_{c}$-B)$^{\alpha }$ . [1] B. Cage, N. S. Dalal, \textit{Chem. Mater.} \textbf{13}, 881 (2001).