Strong enhancement of the critical current at the antiferromagnetic transition in ErNi${}_2$B${}_2$C single crystals

We report on transport and magnetization measurements of the critical current density $J_c$ in ErNi${}_2$B${}_2$C single crystals that show strongly enhanced vortex pinning at the Néel temperature $T_N$ and low applied fields. The height of the observed $J_c$ peak decreases with increasing magnetic field in clear contrast with that of the peak effect found at the upper critical field. Angular transport measurements of $J_c$ revealed the correlated nature of this pinning enhancement, which we attribute to the formation of antiphase boundaries at $T_N$.

Figure 1

(a) PPMS transport measurements of $J_c$ for $\mathbf{H}\parallel c$ and $\theta ={30}^{\circ }$. A new peak in $J_c$ is observed at $T=T_N$ for $\mathbf{H}\parallel c$. The sketch gives the measurement geometry. (b) Contour plot of $J_c$ as a function of temperature and magnetic field $\mathbf{H}\parallel c$ showing the field range where the peak at $T=T_N$ is present (measured in the PPMS).

Figure 2

(a) Angular transport $J_c$ measurements at ${\mu }_{0}H=0.4$ T reveal the narrow temperature range at $T_N$ over which the peak at $\mathbf{H}\parallel c$ occurs (obtained in the He flow system). (b) The contour plot of $J_c$ as a function of magnetic field orientation $\theta$ and $T$ shows the location of the peak at $T_N$ and $\theta =0^{\circ }$ in the $T$-$\theta$ space (measured in the PPMS).

Figure 3

The critical current density vs temperature at ${\mu }_{0}H=0.02\mathrm{T}$ (with $\mathbf{H}\parallel c$), obtained from magnetization measurements, exhibits a local maximum at $T=T_N$.