Nuclear magnetic resonance studies of 75As under uniaxial stress were conducted on theparent and Co-doped BaFe2As2 iron-based superconductors. An NMR strain probe, that incorporates
piezoelectric-based apparatus from Razorbill Instruments, was designed to apply
the uniaxial stress. Nuclear quadrupolar splittings of the parent compound were measured
as a function of strain. The electric eld gradient tensor responds linearly to the presence of
a strain eld in the paramagnetic phase. The nematic susceptibility was extracted from the
slope of this linear response as a function of temperature and it diverges near the structural
transition. The detailed spin-lattice relaxation rate dependence on strain was measured for
the parent BaFe2As2. The magnetic
uctuation spectrum in the paramagnetic phase acquires
an anisotropic response in spin-space upon application of a tetragonal symmetry-breaking
strain eld. This result unveils an internal spin structure of the nematic order parameter,
indicating that electronic nematic materials may oer a route to magneto-mechanical control.
A second horseshoe device was used to apply strain, and the in-plane anisotropy of
spin-lattice relaxation rate under uniaxial stress was measured in Co-doped BaFe2As2. The
anisotropy reaches a maximum of 30% at TN, and the recovery data reveal that the glassy
behavior of the spin
uctuations present in the twinned state persist in the fully detwinned
crystal.
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