Persistent Detwinning of Iron-Pnictide EuFe2As2 Crystals by Small External Magnetic Fields

Our comprehensive study on EuFe2As2 reveals a dramatic reduction of magnetic detwinning fields compared to other AFe(2)As(2) (A = Ba, Sr, Ca) iron pnictides by indirect magnetoelastic coupling of the Eu2+ ions. We find that only similar to 0.1 T are sufficient for persistent detwinning below the local Eu2+ ordering; above T-Eu = 19 K, 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 (190 K). This persistent detwinning provides the unique possibility to study the low temperature electronic in-plane anisotropy of iron pnictides without applying any symmetry-breaking external force.