Field-induced order-disorder transition in the quasi-one-dimensional anisotropic antiferromagnet $\mathrm{Ba}{\mathrm{Co}}_2{\mathrm{V}}_2{\mathrm{O}}_8$

Order-disorder transition is observed in the quasi-one-dimensional anisotropic spin chain antiferromagnet $\mathrm{Ba}{\mathrm{Co}}_2{\mathrm{V}}_2{\mathrm{O}}_8$ in magnetic fields along the magnetic easy $c$ axis below the Néel temperature. We construct the phase diagram in the $H\text{−}T$ plane through magnetic and heat capacity measurements and find that the phase boundary of the order-disorder transition can be described in terms of a mean-field power law. We also suggest that quantum critical behavior from three-dimensional Néel ordering back into a one-dimensional disordered phase is observed in magnetic fields above a critical value of $4.4\mathrm{T}$.

Figure 1

(Color online) Magnetic susceptibilities in $H=1\mathrm{T}$ parallel $\left({\chi }_{\Vert }\right)$ and perpendicular $\left({\chi }_{\perp }\right)$ to the $c$ axis. The solid line is a fit based on 1D $S=3∕2$ linear chain model.

Figure 2

(Color online) Magnetization versus applied field at $2\mathrm{K}$.

Figure 3

(Color online) (a) Low temperature susceptibilities measured in different fields from $0.5\mathrm{T}\text{to}9\mathrm{T}$ parallel to the $c$ axis, and (b) low temperature heat capacity data measured in different fields.

Figure 4

(Color online) (a) Phase diagram of $\mathrm{Ba}{\mathrm{Co}}_2{\mathrm{V}}_2{\mathrm{O}}_8$ in the field $\left(H\right)$ -temperature $\left(T\right)$ plane. Solid line is a fit of $H=H_{\mathrm{c}}{(1-T∕T_{\mathrm{N}})}^{1∕3}$ with $T_{\mathrm{N}}=5.4\mathrm{K}$ and $H_{\mathrm{c}}=4.4\mathrm{T}$. (b) The $c$-axis susceptibilities measured at three different fields (1, 4.4, and $9\mathrm{T}$) showing a magnetic transition at $\sim 5\mathrm{K}$ with almost no change of the broad peak feature at $\sim 30\mathrm{K}$.