Magnetic order or charge-density wave inLa2NiO4by Mössbauer spectroscopy

Measurements of Mössbauer absorption spectra of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$: ${\mathrm{La}}_2$Ni${\mathrm{O}}_4$ at 297, 77, and 4.2 K provide evidence, at the lowest temperatures, of magnetic order in a sample containing ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}_{}^{3+}{}_{}{}^{}$-ion impurities and some ${\mathrm{La}}_{2+n}{\mathrm{Ni}}_{1+n}{\mathrm{O}}_{4+3n}$ intergrowth. Mössbauer emission spectra of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$: ${\mathrm{La}}^2$Ni${\mathrm{O}}_4$ at 77 and 4.2 K show magnetic order coexisting with paramagnetism in a sample containing a small concentration of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$-ion impurities and some ${\mathrm{La}}_{2+n}{\mathrm{Ni}}_{1+n}{\mathrm{O}}_{4+3n}$ intergrowth. These results are interpreted as evidence for competition between magnetic ordering and charge-density-wave formation among electrons of a narrow ${\sigma }_{x^2-y^2}^{*}$ band; intergrowths, impurities, and nonstoichiometry favor magnetic ordering.