Suppression of Biquadratic Coupling in Fe/Cr(001) Superlattices below the Néel Transition of Cr

The Néel temperature ( $T_N$) of Cr in sputtered, epitaxial Fe $/$Cr(001) superlattices is identified via transport and magnetic anomalies. The onset of the antiferromagnetism is at a thickness $t_{\mathrm{Cr}}$ of 42 Å. The bulk value of $T_N$ is approached asymptotically as $t_{\mathrm{Cr}}$ increases and is characterized by a three-dimensional shift exponent. Most strikingly, the biquadratic interlayer magnetic coupling (90° orientation of adjacent Fe layers), observed in the thick Cr regime, is suppressed below $T_N$. These results are attributed to finite-size effects and spin frustration near rough Fe-Cr interfaces.