Family of anisotropic spin glasses Ba1–xLa1+xMnO4+δ

The synthesis, structural, and magnetic characterization of the series Ba1−xLa1+xMnO4+δ (0≤x≤0.5) with the K2NiF4-type structure are reported. We previously found that the x=0.2 member exhibits the very rare anisotropic spin-glass behavior with only the c-axis spin component freezing below Tg. Here we show that each member of the Ba1−xLa1+xMnO4+δ (0≤x≤0.4) series exhibits the same spin-glass behavior. Moreover, Tg varies with x, reaching a maximum of 26.4(4) K for x=0.20 compared with 19.2(2) K for x=0. The spin-glass behavior was confirmed by both dc and ac magnetic susceptibility measurements. No long-range magnetic order was found down to 2 K. All series members adopt the I4/mmm space group and subtle structural transformations occur with increasing La content. The unit cell volume contracts for 0.00.2 a mixed +2/+3 oxidation state was found. Therefore, for the charge balance, samples with x≤0.2 contain excess oxygen as an interstitial species, while for x>0.2, the structure cannot sustain any more interstitial oxygen and the La excess is accommodated through the reduction of some Mn3+ to Mn2+. Based on the oxidation state of Mn, the possible origins of the spin-glass magnetism in the Ba1−xLa1+xMnO4+δ series are discussed.