Two types of magnetic shape-memory effects in Fe_1+yTe

The discovery of superconductivity in β-FeSe triggered considerable interest also in the related tellurium compound Fe_1+yTe. Here we present a detailed experimental study of Fe_1+yTe (y = 0.11 and 0.12) using pulsed magnetic fields up to 60 T. Our studies confirmed two types of magnetic shape memory (MSM) effects in the low temperature antiferromagnetic state of these compounds [1]. Scanning tunneling microscopy measurements at low temperature established a modulated and finely twinned martensitic microstructure. The antiferromagnetism of the monoclinic phase allows for a magnetic–field–induced reorientation of these twin variants by the motion of twin boundaries. At sufficiently high magnetic fields, we observed a second isothermal transformation process. This gives rise to a second MSM effect caused by a phase transition back to the field-polarized tetragonal lattice state [2]. Observation of MSM effects in two known material families [1,3] related to high-T_c superconductors points to a prominent role of electron–phonon coupling arising through the spin–orbit interactions.
[1] S. Rößler et al., Proc. Natl. Acad. Sci. USA, 116, 16697 (2019).
[2] X. Fabreges et al., Phys. Rev. B 95, 174434 (2017).
[3] A. N. Lavrov et al., Nature 418, 385 (2002).