Magneto-optical properties of Fe/Cr/Fe/MgO/Fe structures epitaxially grown on GaAs(001)

Abstract

Fe/Cr/Fe trilayers were epitaxially grown on atomically flat GaAs(001). For the thickness of Cr spacer layer corresponding to antiferromagnetic coupling, “reversed” minor hysteresis loops were measured with longitudinal magneto-optical Kerr effect (MOKE), i.e., a negative “magnetization” signal was detected when the thicker bottom Fe layer was saturated along the applied field. This behavior is interpreted by depth variations of the MOKE sensitivity. Magnetization reversal shows that both antiferromagnetic switching and spin–flop transition fields depend on the ratio of both Fe film thicknesses. The shape of the MOKE loops becomes more complex with further deposition of MgO and Fe layers on the top of the Fe/Cr/F/GaAs(001) stack. Superconducting quantum interference device measurements confirm the interpretation of the MOKE loops and demonstrate homogeneity and sharpness of the interfaces in the structures.

Single-crystalline Fe∕Cr∕Fe∕MgO∕Fe magnetotunnel junctions grown on GaAs(001)

“…7 The lowest switching field obtained in trilayers with strongly different Fe thickness corresponds to the coercivity of the thicker layer and the highest is approached when the thickness of both Fe layers becomes similar. At low fields, the Fe films in the Fe/ Cr/ Fe trilayer switch simultaneously and keep their antiferromagnetic coupling.…”

“…6,7 Such Fe/ Cr/ Fe system, if combined with the Fe/ MgO / Fe MTJ, could remarkably improve the junction operation. An independent magnetization switching in the Fe electrodes was achieved by pinning the magnetization of one of the Fe films by antiferromagnetic coupling across a Cr spacer to another Fe film.…”

Magneto-optical additivity in ferromagnetic bilayers separated by nonferromagnetic spacers

“…8 Briefly, the Fe/ Cr/ Fe sandwiches were grown epitaxially on clean GaAs͑001͒ surfaces with Ga-terminated ͑4 ϫ 6͒-like reconstruction. The Fe and Cr films were deposited at room temperature by electron-beam evaporation at rates from 1 to 1.5 monolayer ͑ML͒ / min and at pressures below 2 ϫ 10 −10 mbar.…”

“…8 More precisely, it was observed in the longitudinal Kerr ellipticity signal that the thicker bottom Fe layer ͑i.e., the one facing the GaAs substrate͒ gives a much smaller contribution to the signal than the thinner top Fe does. Consequently, when the thicker layer magnetization is oriented along the applied magnetic field, then in moderate fields where magnetizations of the both films are still antiparallel, the Kerr ellipticity signal is dominated by the contribution of the thinner top layer magnetized in an opposite direction with respect to the applied field.…”

“…In order to describe quantitatively the effect observed before, 8 we performed a more complete and precise experimental study of the MO response of the Fe/ Cr/ Fe systems on GaAs͑001͒. For a fixed thickness of the bottom layer t b , the thickness of the top one t t was varying in a thickness range large enough to explain conditions under which the reversed loops can be observed.…”