Block Magnetic Excitations in the Orbitally Selective Mott Insulator BaFe_{2}Se_{3}

Area of Science:

• Condensed matter physics
• Materials science
• Magnetism

Background:

• Iron pnictides and selenides exhibit complex magnetic phases due to coupled electronic, orbital, and lattice properties.
• The Fe4 block state is an exotic magnetic ground state found in low-dimensional iron-based magnets.

Purpose of the Study:

• To fully characterize the static and dynamic spin correlations of the Fe4 block state in BaFe2Se3.
• To investigate the role of orbital degrees of freedom in stabilizing exotic magnetic states in iron-based magnets.

Main Methods:

• Powder inelastic neutron scattering was employed to study the magnetic excitations.
• Analysis involved comparing experimental data with predictions from an effective Heisenberg model.

Main Results:

• All predicted magnetic excitations for the Fe4 block state below 300 meV were observed and quantitatively reproduced.
• The measured spectral weight was approximately 2/3 of that expected for localized S=2 moments, indicating missing contributions.

Conclusions:

• The study successfully characterized the spin correlations of the Fe4 block state.
• Orbital degrees of freedom are highlighted as a key factor in stabilizing this exotic magnetic state in iron-based magnets.