Antiferromagnet-induced perpendicular magnetic anisotropy in ferromagnetic Co/Fe films with strong in-plane magnetic anisotropy

Ferromagnetic (FM) films with higher magnetic moment density typically exhibit sizable in-plane magnetic anisotropy as a result of strong dipolar interactions, which hinder their application in state-of-the-art perpendicularly based magnetic devices. This study reports the effects of triggering the perpendicular magnetic anisotropy (PMA) of a Co/Fe film with strong in-plane magnetic anisotropy through nearby antiferromagnetic (AFM) fcc ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ and face-centered tetragonal (e-fct) Mn films. Our results demonstrate that fcc ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ films with a three-dimensional quadratic AFM spin structure can trigger robust PMA in a Co/Fe film through collinearlike AFM-FM exchange coupling at room temperature. Furthermore, by incorporating a monolayered ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ film into the Mn-Co interface or by reducing the temperature, PMA can also be triggered in a Co/Fe film by using e-fct Mn films with an in-plane-oriented AFM spin structure at room or low temperature through noncollinear exchange coupling across the AFM-FM interface. Our results clarify the exchange-coupling mechanisms, characteristic behaviors, and critical conditions for increasing control over antiferromagnet-induced PMA in FM films with high magnetic moment density but strong in-plane magnetic anisotropy, which is helpful for the development of next-generation perpendicularly based spintronic devices.

Figure 1

Selected MEED (0,0) beam intensity curves as a function of deposition time for Fe film grown on Cu(001), Co film grown on 3-ML Fe/Cu(001), and ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ and Mn films grown on 3-ML Co/3-ML Fe/Cu(001) at 300 K. Film thickness was calibrated by the oscillations in the MEED curves. The arrows indicate the time for the shutter to be closed.

Figure 2

LEED patterns of (a) Cu(001), (b)–(d) 4–12-ML ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}/3\text{−}\mathrm{ML}$ Co/3-ML Fe/Cu(001), (e) 3-ML Co/3-ML Fe/Cu(001), and (f)–(h) 4–12-ML Mn/3-ML Co/3-ML Fe/Cu(001) films, measured at 110 eV and 300 K.

Figure 3

Average interlayer distance ($d_{\perp }$) of various (a) ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ and (b) Mn films grown on 3-ML Co/3-ML Fe/Cu(001), as calculated according to the energy peaks ($I$ or $I^{\prime }$) of the corresponding LEED specular spot $I/V$ curves of panels (c) and (d) measured at 300 K. In panel (a), ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ films grown on 3-ML Co/3-ML Fe/Cu(001) exhibit a fcc structure when $t_{\mathrm{FeMn}}$ exceeded 8 ML. In panel (b), Mn films grown on 3-ML Co/3-ML Fe/Cu(001) exhibit an e-fct structure transition when $t_{\mathrm{Mn}}$ exceeded 4 ML. In panels (a) and (b), the arrows represent $d_{\perp }$ of Cu(001). The illustrations display the atomic model of the fcc ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ and e-fct Mn films.

Figure 4

(a) Magnetic hysteresis loops, (b) $M_r$, and (c) $H_c$ of 0- to 10-ML ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}/3\text{−}\mathrm{ML}$ Co/3-ML Fe/Cu(001) measured at 300 K. In panel (b), the yellow shadow indicates the estimated critical thickness for the onset of PMA. In panel (c), the gray shadow indicates the estimated critical thickness for the onset of long-range AFM ordering in the ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ film.

Figure 5

XAS and XMCD curves of 10-ML ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}/3\text{−}\mathrm{ML}$ Co/3-ML Fe/Cu(001) measured at the (a) Co, (b) Fe, and (c) Mn $L_{3,2}$ edges in the remanent states at 300 K. (d) Magnetic hysteresis loops of 10-ML ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}/3\text{−}\mathrm{ML}$ Co/3-ML Fe/Cu(001) measured by MOKE at 300 K. (e) Schematic illustration of the interfacial spin structure of ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ coupled with the FM moments. The bold black arrows displayed in each figure indicate the remanent states of the films ($M_{+}$ or $M_{-}$) under positive or negative out-of-plane-oriented magnetic fields ($\pm 1000$ Oe). The illustrations in the top-right of the figure show the geometry of the XMCD measurement [34] and the 3Q spin structure of the AFM ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ film [18, 19, 20, 21].

Figure 6

Magnetic hysteresis loops of (a) 0- to 6-ML Mn/3-ML Co/3-ML Fe/Cu(001) and (b) 0- to 7-ML Mn/1-ML ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}/3\text{−}\mathrm{ML}$ Co/3-ML Fe/Cu(001) measured at 300 K. (c) Magnetic hysteresis loops of 0- to 6-ML Mn/3-ML Co/3-ML Fe/Cu(001) films measured at 155 K. (d)–(i) Summarized $M_r$ and $H_c$ values based on panels (a)–(c). In panel (d), the yellow shadow indicates the estimated critical thickness for the onset of unsaturated magnetization at 300 K. In panels (f) and (h), the yellow shadows indicate the estimated critical thicknesses for the onset of PMA at 300 and 155 K, respectively. In panels (e), (g), and (i), the gray shadows indicate the estimated critical thicknesses for the onset of an established long-range AFM ordering of Mn films at 300 or 155 K.

Figure 7

(a)–(c) Perpendicular magnetic hysteresis loops of 4- to 8-ML Mn/3-ML Co/3-ML Fe/Cu(001) measured at various temperatures. (d) Perpendicular (solid line) and in-plane (dashed line) magnetic hysteresis loops of 0-, 1-ML Mn/2-ML Co/3-ML Fe/Cu(001) measured at various temperatures. (e) Summarized $H_c$ values based on panels (a)–(c). (f) Critical temperatures for the absence of induced PMA in 4- to 8-ML Mn/3-ML Co/3-ML Fe/Cu(001). In the lower portion of panel (d), a presence of perpendicular magnetic hysteresis loops at low temperature is attributable to enhanced perpendicular interface anisotropy of the interfacial Mn moments in 1-ML Mn/2-ML Co/3-ML Fe/Cu(001). In panel (e), thickening $t_{Mn}$ in Mn/3-ML Co/3-ML Fe/Cu(001) resulted in an increased perpendicular $H_c$ when $T<190\mathrm{K}$ but a reduced perpendicular $H_c$ when $T>190\mathrm{K}$.

Figure 8

XAS and XMCD curves of 6-ML Mn/3-ML Co/3-ML Fe/Cu(001) measured at the (a) Co, (b) Fe, and (c) Mn $L_{3,2}$ edges in the remanent states at 100 K. (d) Magnetic hysteresis loops of 6-ML Mn/3-ML Co/3-ML Fe/Cu(001) measured by MOKE at 155 K. (e) and (f) Schematic illustrations of the magnetic configurations in Mn/3-ML Co/3-ML Fe/Cu(001) in low-temperature ($T<190\mathrm{K})$ and high-temperature regimes ($T>190\mathrm{K})$. The bold black arrows displayed in each figure indicate the remanent states of the films ($M_{+}$ or $M_{-}$) under positive or negative out-of-plane-oriented magnetic fields ($\pm 1000$ Oe). The illustrations in the top part of the figure show the geometry of the XMCD measurement [34] and the in-plane layered AFM spin structure of the e-fct Mn film [22, 23].