Abstract
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.
Highlights
This C4(Ga, Ab, Fc) phase is believed to prevail at all temperatures below TN, and YFeO3 goes through a spin-reorientation transition (SRT) only in the presence of an external magnetic field along the a axis
According to Shapiro et al.26 and Yamaguchi et al.,15 the quasiferromagnetic resonance (qFMR) and quasiantiferromagnetic resonance (qAFMR) mode energies are, respectively, given by where Aaa and Acc are the second-order anisotropy energy, K4 is the fourth-order anisotropy energy, E is an exchange constant, S is the magnetic moment of the sublattice, and h is the angle between the c axis and the direction of weak ferromagnetism (WFM)
We propose to retain this fourth-order anisotropy constant, K4, which originates from the next-nearest neighbor (NNN)
Summary
YFeO3 undergoes a magnetic transition from the high-temperature paramagnetic phase into the low-temperature antiferromagnetic C4 phase at the Neel temperature of TN 1⁄4 650 K.5 In this antiferromagnetic phase, the Fe3þ spins align essentially along the a axis, but the residual Dzyaloshinskii–Moriya (DM) interaction induces canting of the Fe3þ spins, which leads to weak ferromagnetism (WFM) along the c axis.2,6 This C4(Ga, Ab, Fc) phase is believed to prevail at all temperatures below TN, and YFeO3 goes through a spin-reorientation transition (SRT) only in the presence of an external magnetic field along the a axis.7 Such features of YFeO3 have been studied by various techniques including magnetometry,8 neutron scattering,9 Raman spectroscopy,10 and terahertz spectroscopy.11–13. We present our terahertz spectroscopic study of YFe1ÀxMnxO3 (x 1⁄4 0–0.4), focusing on the antiferromagnetic resonance modes and their temperature and Mn doping dependence.
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