Nuclear Magnetic Resonance and Magnetic Susceptibility of SmAl3

The Knight shift of the ${\mathrm{Al}}^{27}$ NMR in Sm${\mathrm{Al}}_3$ has been measured in the temperature region from 78 to 400°K, and the susceptibility of Sm${\mathrm{Al}}_3$ has been measured up to 850°K. The part of the Knight shift arising from polarization of the conduction electrons through exchange with the $4f$ electrons reverses sign at (310±20) °K, and the relation between the Knight shift and the susceptibility is not linear. This behavior results mainly from Van Vleck-type paramagnetism, and could adequately be calculated on the basis of free ${\mathrm{Sm}}^{3+}$ ions. The parameters used are the multiplet splitting constant $\frac{A}{k}=(410\mathrm{}\pm 20)°$K, and the interionic exchange constant $\frac{{\mathcal{I}}_{\mathrm{ff}}}{k}=-(15\mathrm{}\pm 5)°$K, indicating antiferromagnetic ordering at low temperatures. The effective exchange constant between the conduction-electron spins and the $4f$-electron spins has been found to be ${\mathcal{I}}_{\mathrm{sf}}=-0.21\mathrm{}$ eV, equalling those derived for other R${\mathrm{Al}}_3$ compounds (R=rare earth). The nuclear quadrupole coupling has been measured to be $\frac{\left|e^{2}qQ\right|}{h}=(0.8\mathrm{}\pm 0.1)$ Mc/sec, and is discussed in terms of the point-charge model.