Ferro- and antiferromagnetism in oxychalcogenides LnCrOX2 (Ln = La or Nd and X = S or Se)

The two isomorphous compounds LaCrOS₂ and LaCrOSe₂ are ferromagnetic (T_c = 35 and 51 K, respectively). This implies ferromagnetic super-superexchange interactions. NdCrOS₂ is antiferromagnetic (T_N = 72 K) and undergoes a spin-flop transition (H_c = 54 KOe at 20 K). The study of the thermal variation of Cr³⁺ and Nd³⁺ magnetic moments below T_N allows a rough estimate of the Cr---Nd and Cr---Cr exchange fields ratio (0.1).