Terahertz spectroscopy of antiferromagnetic resonances in YFe_1-xMn_xO₃(0 ≤ x ≤ 0:4) across a spin reorientation transition

We have conducted a terahertz spectroscopic study of antiferromagnetic resonances in bulk orthoferrite YFe1-xMnxO3 0 ≤ x ≤ 0.4. Both the quasi-ferromagnetic resonance mode and the quasi-antiferromagnetic resonance mode in the weak ferromagnetic Γ4 phase disappear near the spin reorientation temperature, TSR, for the onset of the collinear antiferromagnetic Γ1 phase (x ≥ 0.1). Below TSR, an antiferromagnetic resonance mode emerges and exhibits a large blueshift with decreasing temperature. However, below 50 K, this mode softens considerably, and this tendency becomes stronger with Mn doping. We provide a deeper understanding of such behaviors of the antiferromagnetic resonance modes in terms of the influence of the Mn3+ ions on the magnetocrystalline anisotropy. Our results show that terahertz time-domain spectroscopy is a useful, complementary tool in tracking magnetic transitions and probing the interaction between disparate magnetic subsystems in antiferromagnetic materials with multiple ionic species.