Tunable Magnetostriction and Near-Zero Thermal Expansion in Fe-Doped Ferrimagnetic HoCo ₂

This research systematically investigates the regulation of the magnetostriction and thermal expansion properties in the Fe-doped HoCo 1.75 Fe 0.25 Laves-phase intermetallic compounds. By means of synchrotron X-ray diffraction, neutron powder diffraction, magnetic property measurements, and magnetostriction and thermal expansion characterizations, it is found that HoCo 1.75 Fe 0.25 retains the MgCu 2 -type C15 structure (space group: Fd 3̅ m ) at room temperature and exhibits near-zero thermal expansion (+1.69 × 10 –6 K –1 ) within a wide temperature range of 24–273 K. Notably, the Fe doping causes the magnetostriction coefficient to change from positive to negative. A magnetic phase transition transforms from a first order to a second order, and the magnetic entropy peak broadens and shifts to 270 K. Neutron powder diffraction confirms the ferrimagnetic order, where the magnetic moments of Ho atoms and Co/Fe atoms are aligned antiparallel. A significant positive linear correlation between the magnetic moment of Ho atoms and the lattice volume is observed, which gives rise to a strong magnetovolume effect for tuning thermal expansion and magnetostriction.