Influence of the substrate on structure and magnetic properties of Co–N thin films

Structural and magnetic properties of stoichiometric Co4N epitaxial thin films

“…The N self-diffusion process obtained for the Co-N system can now be used to understand the formation of Co 4 N thin films. We find that in previous works the Co 4 N phase was always synthesized at T s 525 K [20][21][22][23][24][25][26][27]. Comparing the LP of Co 4 N films obtained in those works, we find that the LP was much smaller than the theoretically predicted value of 3.735 Å [18] [20,33].…”

“…From bulk magnetization measurements (shown in Supplemental Material [43]), we found that saturation magnetization (M s ) of both samples is about ≈ 1200 emu/cm 3 (1 emu/cm 3 = 10 3 A/m). Comparing the experimental values of M s for Co 4 N films obtained so far in the literature, a large variation can be seen ranging between 485-1300 emu/cm 3 [19][20][21][23][24][25]28]. As pointed out before, the formation of stoichiometric Co 4 N phase itself is questionable, the large difference in M s can stem from: (i) error in volume measurement of film, (ii) intermixing taking place at the substrate-film interface, (iii) surface oxidation/contamination etc.…”

“…However, as even the phase diagram of the Co-N has not been established yet, the recipe for formation of Co 4 N phase is ambiguous. Due to this, the Co 4 N has not been explored much experimentally and the available experimental reports are contradicting, e.g., the lattice parameter (LP) of Co 4 N have been found between 3.59 to 3.52 Å [19][20][21][22][23][24][25][26][27] while its theoretical value is 3.735 Å [18]. Similarly, the M s of Co 4 N was found to vary in a rather large range between 485 and 1300emu/cm 3 [20,21,[23][24][25][26][27][28].…”

“…Due to this, the Co 4 N has not been explored much experimentally and the available experimental reports are contradicting, e.g., the lattice parameter (LP) of Co 4 N have been found between 3.59 to 3.52 Å [19][20][21][22][23][24][25][26][27] while its theoretical value is 3.735 Å [18]. Similarly, the M s of Co 4 N was found to vary in a rather large range between 485 and 1300emu/cm 3 [20,21,[23][24][25][26][27][28]. Since the LP of fcc Co is about 3.54 Å [18], it appears that Co 4 N thin films prepared so far might have a significant fraction of fcc Co. Theoretically, it is expected that N at.% tend to decreases monotonically with LP [18,29] and therefore, a correlation can be made between the substrate temperature (T s ) used to deposit Co 4 N and their corresponding measured LP.…”

Phase formation, thermal stability and magnetic moment of cobalt nitride thin films

“…[11][12][13][14][15][16][17][18][19] Recent theoretical calculations predicted that the spin polarization ratio for Co 4 N is even higher than that of Fe 4 N. 20,21 This has led to somewhat renowned interests in the Co-N system both theoretically and experimentally. [22][23][24][25][26][27][28] Though theoretical studies predict that under large-volume high-moment approach, the magnetic moment of Co 4 N can be larger than Co, 9 experimental results always find a value much smaller than pure Co, for Co 4 N thin films. 22 This can be understood as in all Co 4 N thin films reported so far the value of a has always been smaller than the value predicated theoretically.…”