Andreas Sieber, Grégory Chaboussant, Roland Bircher, Colette Boskovic, Hans U. Güdel, George Christou and Hannu Mutka
Pressure dependence of the magnetic anisotropy in the single-molecule magnet Mn₄O₃Br(OAc)₃(dbm)₃
Phys. Rev. B 70, 172413/1-4 (2004)                 

Abstract: The anisotropy splitting in the ground state of the single-molecule magnet Mn₄O₃Br(OAc)₃(dbm)₃ is studied by inelastic neutron scattering as a function of hydrostatic pressure. This allows a tuning of the anisotropy and thus the energy barrier for slow magnetization relaxation at low temperatures. The value of the negative axial anisotropy parameter D_cluster changes from –0.0627(1)  meV at ambient to –0.0603(3)  meV at 12  kbar pressure, and in the same pressure range the height of the energy barrier between up and down spins is reduced from 1.260(5)  meV  to  1.213(9)  meV. Since the Mn-Br bond is significantly softer and thus more compressible than the Mn-O bonds, pressure induces a tilt of the single ion Mn³⁺ anisotropy axes, resulting in the net reduction of the axial cluster anisotropy.