The synthesis, structural, and magnetic characterization of the series ${\mathrm{Ba}}_{1-x}{\mathrm{La}}_{1+x}\mathrm{Mn}{\mathrm{O}}_{4+\delta }$ ($0\le x\le 0.5$) with the ${\mathrm{K}}_2\mathrm{Ni}{\mathrm{F}}_4$-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 $T_{\mathrm{g}}$. Here we show that each member of the ${\mathrm{Ba}}_{1-x}{\mathrm{La}}_{1+x}\mathrm{Mn}{\mathrm{O}}_{4+\delta }$ ($0\le x\le 0.4$) series exhibits the same spin-glass behavior. Moreover, $T_{\mathrm{g}}$ 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 $0.0<x<0.3$ and expands for $0.3<x\le 0.5$. Similar behavior is seen for the equatorial Mn-O bonds in the Mn-O octahedron while the axial Mn-O distances increase to $x\sim 0.3$ but remain unchanged for higher $x$. X-ray absorption near-edge structure analysis revealed that the oxidation state of Mn in the ${\mathrm{Ba}}_{1-x}{\mathrm{La}}_{1+x}\mathrm{Mn}{\mathrm{O}}_{4+\delta }$ samples varies with $x$: For $x\le 0.2$ Mn is in the +3.0(1) oxidation state only, while for $x>0.2$ a mixed +2/+3 oxidation state was found. Therefore, for the charge balance, samples with $x\le 0.2$ 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 ${\mathrm{Mn}}^{3+}$ to ${\mathrm{Mn}}^{2+}$. Based on the oxidation state of Mn, the possible origins of the spin-glass magnetism in the ${\mathrm{Ba}}_{1-x}{\mathrm{La}}_{1+x}\mathrm{Mn}{\mathrm{O}}_{4+\delta }$ series are discussed.

• Received 6 February 2021
• Revised 20 May 2021
• Accepted 10 June 2021

DOI:https://doi.org/10.1103/PhysRevMaterials.5.074403