Evolution of the normal-to-magnetically ordered state in substituted BaFe2As2: a microscopic point of view

GUILLERME G. LESSEUX; THALES M. GARITEZI; MÁRIO M. PIVA; PRISCILA F. S. ROSA; DINA TOBIA; MARTIN SALETA; EDUARDO GRANADO; P. KUHNS; A. REYES; X. WANG; T. GRANT; Z. FISK; C. ADRIANO; R. M. FERNANDES; PASCOAL G. PAGLIUSO; RICARDO URBANO

San Diego

Conferencia; 13th Joint MMM-Intermag Conference; 2016

The discovery of high-temperature superconductivity in the iron-pnictides in 2008 triggered a massive amount of scientific inquiries. Since then, much has been learned about the novel forms of quantum matter and a reasonable understanding of the nature of the superconducting state itself has been accomplished. However, unresolved issues include the complexity of the consecutive phase transitions at elevated temperatures in the phase diagram of these materials. Here we report a detailed microscopic investigation of the structural/nematic-magnetic transitions in pure and slightly substituted BaFe2As2 single crystals by means of high-resolution synchrotron x-ray diffraction and high field Nuclear Magnetic Resonance. The combination of these techniques, along with specific heat measurements, revealed that a structural tetragonal-to-orthorhombic transition spontaneously emerges prior to a paramagnetic-to-antiferromagnetic (spin density wave) one. The transition temperatures are well distinguished and our results undoubtedly show the presence of short ranged magnetic order in the orthorhombic phase within the finite temperature range between the transitions. The balance of entropy associated with these transitions as revealed by the heat capacity data is well described by a theoretical model in which spin fluctuations drive the structural/nematic transition.