Tuning Magnetism of Metal-Organic Framework by Different Types of Pressure.

The properties of metal-organic frameworks (MOFs) are expected to be sensitive to external pressures because of their inherently flexible structures. Although pressure-driven structural transitions have been intensively studied, the influence of pressure on magnetism has been less exploited for MOFs. Especially, the efficiency of applied pressure may strongly depend on the pressure-transmitting medium (PTM), which may have a complex interaction with MOFs. Here, the distinctive effects of different types of pressure are reported, including isotropic hydrostatic pressure, quasi-hydrostatic pressure, and uniaxial pressure, on the anisotropic magnetism of the perovskite MOF, [CH3NH3][Co(HCOO)3]. It is found that the hydrostatic pressure has the minimal effect, whereas the uniaxial pressure has the highest efficiency in tuning magnetization and magnetic anisotropy of the MOF. First-principles calculations reveal that the applied low pressures do not significantly alter the superexchange pathways, while local distortions of the CoO6 octahedra emerge as the dominant factor governing magnetic modulation. Moreover, the weakening of hydrogen bonds under uniaxial pressure is proposed to be the primary mechanism responsible for the suppression of single-ion magnetism. These findings underscore the potential applications of directional pressure in precisely controlling the magnetic and electronic properties of MOFs.