Figure 3. Magnetic structure and weak ferromagnetism of KBiFe₂O₅.

(a) Experimental (circles), calculated (line), and difference (“noise” at bottom) NPD profiles for KBiFe₂O₅ at 300 K. Vertical bars indicate calculated positions of Bragg peaks from the nuclear phase (upper) and the magnetic phase (lower). λ = 1.5403 Å. Space group P2₁cn, No. 33, a = 7.9855(1) Å, b = 11.8225(1) Å, c = 5.7396(1) Å, V = 541.87(1) ų; R_wp = 0.0373, R_p = 0.0316, χ² = 1.230. Magnetic symmetry of Shubnikov group: P2₁′cn′ with Fe moment of 3.77(2) μ_B along c-axis direction. (Inset: Refinement with nuclear phase only. Difference profile shows reflections from magnetic phase). (b) Magnetic and crystal structure of KBiFe₂O₅ (P2₁cn cell). (c) Experimental (circles), calculated (line), and difference (“noise” at bottom) NPD profiles for KBiFe₂O₅ at 4 K under 6 T magnetic field. Vertical bars indicate the calculated positions of Bragg peaks from the nuclear phase P2₁cn (upper), from the G-type antiferromagnetic phase P2₁′cn′ (lower), and from the ferromagnetic phase P2₁c′n′ at 6 T (bottom). λ = 1.5403 Å. R_wp = 0.0619, R_p = 0.0490, χ² = 1.348. (d) Temperature dependence of the magnetic (110) reflection indicative of a magnetic phase transition at ~560 K. (e) Magnetization (M) measured at three fields showing near coincidence of ZFC and FC data except at the lowest temperature at 1 kOe and 2 kOe. Magnetic transition at 2 kOe occurs at about 550 K. (f) Magnetization-field (H) curves at 3 K, 30 K and 300 K.