Measurement of a Pauli and Orbital Paramagnetic State in Bulk Gold Using X-Ray Magnetic Circular Dichroism Spectroscopy

We show that bulk gold (Au) exhibits temperature-independent paramagnetism in an external magnetic field by x-ray magnetic circular dichroism spectroscopy at the Au $L_2$ and $L_3$ edges. Using the sum-rule analysis, we obtained a magnetic moment of $1.3\times {10}^{-4}{\mu }_B/\mathrm{atom}$ in an external magnetic field of 10 T and a paramagnetic susceptibility of $8.9\times {10}^{-6}$ for the $5d$ orbit. The induced paramagnetism in bulk Au is characterized by a large ($\approx 30\%$) orbital contribution. This orbital component was retained even when Au atoms formed nanoparticles, playing an important role in stabilizing the spontaneous spin polarization in the Au nanoparticles.

Figure 1

XMCD spectra of an Au foil at the Au (a) $L_3$ and (c) $L_2$ edges, measured at 2.3 K and $\pm 10$, $+6$, and $+2\mathrm{T}$; corresponding XAS spectra at the Au (b) $L_3$ and (d) $L_2$ edges at $+10\mathrm{T}$.

Figure 2

Element-specific magnetization curves of Au foil drawn from the XMCD structure $A$ at (a) 2.2, (b) 10.7, (c) 50.4, (d) 102, and (e) 300 K between $\pm 10\mathrm{T}$. (f) The slope of the magnetization curves, $d(\Delta \mu )/dH$, as a function of temperature.

Figure 3

(a) XMCD spectra at the Au $L_3$ edge, as a function of temperature at 10 T. The spectra are shown with adequate vertical offsets for better presentation, and the dashed lines show the origin of XMCD values for each spectra. (b) Amplitude of the XMCD structure, $A$, at 2 T (triangles), 6 T (circles), and 10 T (squares), as a function of temperature.

Figure 4

XMCD spectra of PAAHC-Au NPs [5] at the Au (a) $L_3$ and (b) $L_2$ edges at 2.3 K and at 10 T, compared with the XMCD spectra of bulk Au.