Perpendicular magnetic anisotropy and noncollinear magnetic structure in ultrathin Fe films on W(110)

Abstract

We used nuclear resonant scattering (NRS) of synchrotron radiation to investigate the details of the thicknessinduced spin reorientation transition (SRT) in ultrathin epitaxial iron films on W(110), where the thicknesses of the films ranged from 1-5 monolayers. During growth, the magnetization of the Fe film, which was probed by the hyperfine magnetic field, changes from a noncollinear configuration with an out-of-plane magnetic component to the homogeneously magnetized state with the in-plane [1-10] easy direction. The fast acquisition of the experimental NRS spectra combined with the high sensitivity of this technique to the orientation of the hyperfine magnetic fields allowed us to study the magnetic evolution during SRT in detail. Our results reveal the complex character of this transition, which has been intensively studied in the past. The noncollinear magnetic structure appears in the system of the mono-, double-, and trilayer areas that coexist due to deviation from the layer-by-layer growth of iron on W(110). We also report the observation of out-of-plane magnetic anisotropy in the double-layer areas at temperatures as high as 300 K. By comparing the experimental results with density functional theory calculations, we conclude that surface magnetic moments are enhanced by 25%.

Magnetic phase diagram of an Fe monolayer on W(110) and Ta(110) surfaces based onab initiocalculations

“…3(a) [24]. It is worth noting that a double layer of Fe on W(110) has an out-of-plane easy axis [11,48], similarly to the case here for large relaxation.…”

Work function and cohesion properties of W–Fe interfaces

“…Fe(100)/W(100), Fe(110)/W (110), W(100)/Fe(100), and W(110)/Fe(110), in which the first and second parts refer to overlayer and substrate, respectively. It should be noted that these settings of interface structures are just to simulate the experimental epitaxial growth of Fe on W (Fe/W interface) as well as W on Fe (W/Fe interface), and that the orientations of (110) and (100) are consistent with the experimental observations [2][3][4][5][6][7][8][9][10][11][12]. Accordingly, a surface unit cell of 1 Â 1 is chosen for each interface model, and the ferromagnetic states are added to Fe films.…”

“…During recent years, the growth of Fe films on the substrate of W, i.e., Fe/W interface, has attracted a lot of research interests among scientists, mainly due to its fascinating magnetic properties as a function of overlayer thickness [1][2][3][4][5][6][7][8][9][10][11][12]. Another well-studied property of various Fe/W interfaces is the work function, which seems very important for the performances of the Fe/W materials utilized as the promising source of spin-polarized electrons of field emission tips [13][14][15][16][17].…”

Evolution of magnetism on a curved nano-surface

“…At 25 Å thick iron layer, the evaluation of the time spectra revealed, that in the lower part of the cap, the magnetic moments points along the Z direction and has ~25% magnetic fraction while on the top, the orientation is intermediate or lies in the X-Y plane with about 50% contribution to the whole spectrum. It is known that ultrathin iron film can exhibit complex magnetic structures up to several monolayers [50][51][52] . Internal stress or asymmetric crystal lattice can also be the source of magnetic anisotropy 30 .…”