Measurement of magnetic moments of free ${\mathrm{Bi}}_N{\mathrm{Mn}}_M$ clusters

Magnetic properties of free ${\mathrm{Bi}}_N{\mathrm{Mn}}_M$ clusters ($N=2–20$, $M=0–7$) are determined from Stern-Gerlach deflections at low temperature $\left(46.5\mathrm{K}\right)$. Pure bismuth clusters with odd number of atoms exhibit paramagnetic deflections. The addition of manganese atoms produces a ferromagnetic response which is strongly size dependent. Certain combinations have very large magnetic moments such as ${\mathrm{Bi}}_5{\mathrm{Mn}}_3$, ${\mathrm{Bi}}_9{\mathrm{Mn}}_4$, ${\mathrm{Bi}}_{10}{\mathrm{Mn}}_5$, and ${\mathrm{Bi}}_{12}{\mathrm{Mn}}_6$.

Figure 1

Position-sensitive time-of-flight spectrum of two adjacent peaks in the mass spectrum, ${\mathrm{Bi}}_{14}\mathrm{Mn}$ $\left(2981\mathrm{amu}\right)$ and ${\mathrm{Bi}}_{13}{\mathrm{Mn}}_5$ $\left(2992\mathrm{amu}\right)$. The dashed thin line is without magnetic field applied $(B=0)$ and the solid line is with $B=0.91\mathrm{T}$. The shift in the mass peaks with the magnet on is due to the deflections. In this case, the ${\mathrm{Bi}}_{14}\mathrm{Mn}$ is shifted by $0.04\mathrm{mm}$ and ${\mathrm{Bi}}_{13}{\mathrm{Mn}}_5$. is shifted by $0.56\mathrm{mm}$.

Figure 2

Deflection profiles of pure bismuth clusters ${\mathrm{Bi}}_N$, $N=3$, 5, and 9. The thin dashed line is without magnetic field $(B=0)$ and the solid line is with $B=0.91\mathrm{T}$. Notice that the trimer deflects both towards high field (the right in the figure) and lower field (left), but the pentamer deflection is single sided. For the latter, the deflection is given by the Langevin equation.

Figure 3

Magnetic moments of pure bismuth clusters determined from their magnetization ($B=0.91\mathrm{T}$, $T=46.5\mathrm{K}$).

Figure 4

Magnetic moments of ${\mathrm{Bi}}_N{\mathrm{Mn}}_M$. Note the particularly large moments of ${\mathrm{Bi}}_5{\mathrm{Mn}}_3$, ${\mathrm{Bi}}_9{\mathrm{Mn}}_4$, ${\mathrm{Bi}}_{10}{\mathrm{Mn}}_5$, and ${\mathrm{Bi}}_{12}{\mathrm{Mn}}_6$.

Figure 5

Magnetic moments of ${\mathrm{Bi}}_N{\mathrm{Mn}}_M$ as a function of $N$ and $M$. The diameters of the circles are proportional to the total moments of the clusters. The data for pure manganese clusters are from Ref. 4.

Figure 6

Histogram of the magnetic moments per Mn atom for clusters ${\mathrm{Bi}}_N{\mathrm{Mn}}_M$ observed in these experiments with more than two Mn atoms. The distribution is bimodal. The peak at $3{\mu }_B$ is identified with ferromagnetic coupling between Mn moments; the peak at $1.3{\mu }_B$ is identified with ferrimagnetic coupling.