Reduced effective magnetization and slow-relaxing impurity damping in strained γ-Fe₂O₃

The ferrimagnetic insulating iron oxide phase γ-Fe₂O₃ (maghemite) finds application as a magnetic nanoparticle in recording media. We report the successful pulsed laser deposition (PLD) of strained tetragonal maghemite thin films on cubic MgO (001) substrates. To investigate its magnetization dynamic, we perform vector network analyzer (VNA) based broadband ferromagnetic resonance experiments and study the magnetization dynamics parameters as function of layer thickness and temperature in a cryogenic set-up. We verify the expected temperature-dependence of the slow-relaxing impurity contribution and observe a complete freeze-out of slow relaxing impurity damping at T=2.5 K. Furthermore, we observe a strain-induced reduction and sign-reversal of the effective magnetization for cryogenic temperatures. The reduced effective magnetization of maghemite makes it an interesting material platform as the associated nearly circular magnetization precession reduces nonlinear magnon damping effects as for example recently demonstrated by us in all-electrical magnon transport experiments [1].

 

[1] J. Gückelhorn et al., arxiv: 2108.03263