Summary of measured physical characteristics: Raman spectroscopy I_D/I_G-ratio, four-point probe sheet resistance (Ω □⁻¹), and XPS wide scan atomic concentrations (at%).

Fe at%	Raman ID/IG	Sheet resistance	XPS wide at%
			Fe 2p	O 1s	C 1s
ta-C	0.15 ± 0.08	—	—	4.2 ± 0.2	95.6 ± 0.2
2	0.22 ± 0.02	3.9 × 108	0.4 ± 0.0	5.7 ± 0.0	93.7 ± 0.1
5	0.25 ± 0.04	2.4 × 105	1.2 ± 0.0	7.5 ± 0.1	90.9 ± 0.1
10	0.37 ± 0.02	7.6 × 104	2.5 ± 0.0	10.6 ± 0.4	86.4 ± 0.6