Magnetic Properties of an Amorphous Antiferromagnet

The magnetic and physical properties of the amorphous antiferromagnetic MnO‐P 2 O 5 glass system were investigated. The glasses were found to be microstructurally homogeneous and amorphous within the detection limit of vacuum Guinier‐De Wolff X‐ray tenchiques. The magnetic properties of the glasses are interpreted in terms of antiferromagnetically coupled Mn 2+ ions, which experience negative exchange interactions with 1,2, or 3 near neighbors, and structurally isolated Mn 2+ ions, which experience weak exchange interactions. The ions which experience weak exchange interactions produce a downward curvature of the inverse‐susceptibility‐vs‐temperature plot at low temperatures. The magnetization‐vs‐field data exhibit curvature toward the field axis, and the magnetization increases as the temperature is decreased to 1.73°K. Below this temperature, the magnetization becomes weakly temperature‐dependent, and the M‐vs‐H curves almost superimpose. These results are interpreted in terms of a 2‐spin Heisenberg model of antiferromagnetism.