Paramagnetism with anomalously large magnetic susceptibility in $\beta$(fcc)-cobalt probed by x-ray magnetic circular dichroism up to 170 GPa

We present direct observation of the magnetic state in a $\beta$(fcc)-Co high-pressure phase accompanied by the $\epsilon \to \beta$ (hcp $\to$ fcc) transition by means of Co $K$-edge x-ray magnetic circular dichroism up to 170 GPa. In contrast to the prediction made in previous studies that $\beta$(fcc)-Co is nonmagnetic, this study concludes that $\beta$(fcc)-Co is paramagnetic with anomalously large magnetic susceptibility $\chi =1.5(4)\times {10}^{-3}$ ${\text{cm}}^3/\text{g}$.

Figure 1

The upper part shows the $K$-edge XANES profiles of Co up to 170 GPa. For clarity, each profile is shifted upward. The closed circles indicate the energy position of the characteristics labeled $a$–$d$. The lower part displays calculated XANES profiles of Co with assumed crystal structures. The calculation was performed using the feff 8.4 code.[16, 17]

Figure 2

(a) Normalized XANES profiles plotted as functions of $(E-E_0)/E_d$. (b) Enlarged figure at the vicinity of peaks $b$, $b^{\prime }$, $c$, and $c^{\prime }$. (c) Pressure dependence of the integrated intensity of XANES around $b$($b^{\prime }$) and $c$($c^{\prime }$).

Figure 3

Co $K$-edge XMCD spectra of Co at selected pressures. For clarity, each spectrum is shifted upward. The colored area indicates the energy range for evaluating the integrated XMCD.

Figure 4

(a) Integrated intensity of XMCD, $I_{\text{XMCD}}$, as a function of pressure (solid circles). Solid lines are guides to the eye. (b) Magnetic field dependence of the XMCD amplitude of peak $A$ at 153 GPa.