Magnetic Characteristics of Some Intermetallic Compounds between Manganese and the Lanthanide Metals

Abstract

The lanthanide metals have been observed to form a large number of intermetallic compounds with the transition metals of the first long period. The compounds have compositions corresponding to the formulas ${\mathrm{AB}}_2$ and ${\mathrm{AB}}_5$ , in which $A$ represents the lanthanide and $B$ is Fe, Co, Ni, or Mn. In previous studies [K. Nassau, L. V. Cherry, and W. E. Wallace, J. Phys. Chem. Solids 16, 123 and 131 (1960)] the $\mathrm{A\hspace{0.17em}}{\mathrm{Co}}_5$ compounds were found to exhibit unusual magnetic behavior. The present study, which deals with the seven isomorphous $\mathrm{A\hspace{0.17em}}{\mathrm{Mn}}_5$ compounds in which $A$ is Sm, Gd, Tb, Dy, Ho, Er, and Y, was undertaken to ascertain whether this is also the case when the $B$ component is Mn. The magnetization-temperature behavior of these compounds has been investigated between 80–550°K. Curie points were observed in all cases, the Curie temperature diminishing steadily with increasing atomic number from 465°K for ${\mathrm{GdMn}}_5$ to 415°K for ${\mathrm{ErMn}}_5$ . The Curie temperature for ${\mathrm{YMn}}_5$ was found to be 490°K. For all the compounds, except ${\mathrm{YMn}}_5$ , the magnetization increases rapidly with decreasing temperature near 80°K, suggesting the existence of a second Curie point. This may be caused by the onset of the alignment of the lanthanide moments or, since there are at least two crystallographically distinguishable Mn's present, to ordering of the moments of a second type of Mn. Saturation magnetizations are presented for 80 and 298°K. The values (in Bohr magnetons per $\mathrm{A\hspace{0.17em}}{\mathrm{Mn}}_5$ unit) at 80°K range from 1.72 for ${\mathrm{SmMn}}_5$ to 6.23 for ${\mathrm{GdMn}}_5$ . The corresponding value for ${\mathrm{YMn}}_5$ is 2.21. These data seem to indicate that the lanthanide moments are aligned in some way at low temperatures, but knowledge of the details of the manner of coupling must await further work.