Nature of magnetism and magnetic-field-induced transitions in non-collinear antiferromagnet Er₂O₃

The nature of magnetism in Er₂O₃ is investigated by detailed studies of the temperature (2–300 K) and magnetic field (up to 90 kOe) dependence of the magnetization M of powder sample of Er₂O₃. The results show paramagnetic to antiferromagnetic (AFM) transition occurring at T_N=3.3 K. For T>T_N the magnetic susceptibility vs. temperature data follows the Curie–Weiss (χ=C/(T−θ)) variation with θ=−10.2 K and magnetic moment μ=6.68μ_B/Er³⁺ ion determined from C. Molecular field model is used to determine the nn (nnn) exchange constants J₁(J₂)=−0.57 K (−3.38 K). The M vs. H data at 2 K analyzed in terms of dM/dH vs. H variations show two field-induced transitions, the first one at H_SF≃15kOe and the second one at H_S≃31kOe. Arguments and analysis are presented to show that H_SF represents the spin-flop transition whereas for H>H_S, the system is field-aligned ferromagnetically since the calculated value of H_S for ferromagnetic ordering using the above magnitudes of J₁ and J₂ agrees well with the experimental H_S. The temperature dependence of H_SF is shown to follow the normalized Brillouin function variation for spin S=1/2 valid for Er₂O₃. The magnetic field dependence of T_N is measured and shown to follow the equation: T_N(H)=T_N(0)−D₁H², expected for antiferromagnets. - Highlights: • Magnetization of Er₂O₃ is reported for 2–300 K in H up to 90 kOe. • Data for T>T_N=3.3K give μ=6.68μ_B/Er³⁺ and exchange J₁(J₂)=−0.57 K(−3.38 K). • Magnetization vs. H data at 2 K yields transitions at H_SF=15 kOe and at H_S=30 kOe. • H_SF is a spin-flop transition and for H>H_S, Er₂O₃ is a ferromagnet. • Variation of T_N with H is shown to follow the equation: T_N(H)=T_N(0)−D₁H²