Persistent detwinning of iron pnictides by small magnetic fields
  Our comprehensive study on EuFe$_2$As$_2$ reveals a dramatic reduction of magnetic detwinning fields compared to other AFe$_2$As$_2$ (A = Ba, Sr, Ca) iron pnictides by indirect magneto-elastic coupling of the Eu$^{2+}$ ions. We find that only 0.1T are sufficient for persistent detwinning below the local Eu$^{2+}$ ordering; above $T_\text{Eu}$ = 19K, higher fields are necessary. Even after the field is switched off, a significant imbalance of twin domains remains constant up to the structural and electronic phase transition (190K). This persistent detwinning provides the unique possibility to study the low temperature electronic in-plane anisotropy of iron pnictides without applying any symmetrybreaking external force. 
S. Zapf, C. Stingl, K. W. Post, J. Maiwald, N. Bach, I. Pietsch, D.   Neubauer, A. Loehle, C. Clauss, S. Jiang, H. S. Jeevan...
cond-mat.supr-con cond-mat.str-el