Exchange bias in (Pt/Co0.9Fe0.1)n/FeMn multilayers with perpendicular magnetic anisotropy

Abstract

We report the observation of exchange bias in (Pt/Co0.90Fe0.10)n/FeMn multilayers, with perpendicular magnetic anisotropy. We analyze the behavior of the exchange-bias field Heb as a function of temperature, FeMn thickness, number of (Pt/Co0.90Fe0.10) bilayers, and annealing conditions. Measurements carried out with field applied perpendicular to the plane of the samples indicate that the hysteresis loops present 100% of remanent magnetization, with Heb reaching 200 Oe and a tunable coercive field, depending on Co and Pt thickness ratio and on Pt buffer thickness. Furthermore, spin-valves of the form (Pt/Co0.90Fe0.10)n/NM/(Co0.90Fe0.10/Pt)m/Co0.90Fe0.10/FeMn with NM=Cu or Pt have been prepared. They exhibit two well separated hysteresis loops when the field is applied perpendicular to the plane.

Correlation between perpendicular exchange bias and magnetic anisotropy in IrMn∕[Co∕Pt]n and [Pt∕Co]n∕IrMn multilayers

“…A similar reduction of the perpendicular magnetic anisotropy has also been found for CoFe/ Pt multilayers with an FeMn film on top. 9 Figure 5 summarizes the effective magnetic anisotropy for different Co/ Pt bilayer repetitions.…”

“…[17][18][19][20][21][22] Although rather small, the perpendicular interfacial exchange energies for the Co/ Pt-IrMn system are comparable to those measured on similar CoFe/ Pt and Co/ Pt multilayers with an AFM FeMn film on top. 9 To determine the effects of field annealing on the perpendicular magnetic anisotropy of exchange-biased Co/ Pt multilayers we measured the EHE voltage with an in-plane FIG. 1.…”

“…Among them are Co/ Pt multilayers with CoO ͑Refs. 4-7͒ and NiO, 8 Co/ Pt, CoFe/ Pt, Co/ Pd, and FeNi/ FeMn multilayers with FeMn, [9][10][11][12][13][14][15] and NiFe/ CoO multilayers. 16 Although these systems are interesting for fundamental studies of the exchange bias phenomenon, the low blocking temperature of CoO and NiO and the low corrosion resistance of FeMn limit their application potential.…”

Out-of-plane exchange coupling between epitaxial Ni (50 Å) and NiO (600 Å) bilayers

“…No coercivity enhancement has been observed. A similar lack of coercivity enhancement in exchange-coupled systems has been seen in (Pt/Co 0.9 Fe 0.1 )n/FeMn multilayers with perpendicular anisotropy 4 and in FeNi/FeMn bilayers 14 for FeMn thicknesses above 100 Å, and has been ascribed to the pinning of AF spins due to the AF anisotropy.…”

“…Recently, exchange coupling has been found in FM/AF systems with a ferromagnetic out-of-plane easy axis. [3][4][5][6] Pt/Co or Pt/CoFe multilayers are used as the FM layer with out-of-plane anisotropy. In Co/Pt multilayers exchange-biased with naturally oxidized thin CoO ͑10 Å͒, 3 a model has been proposed to show that out-of-plane AF spin components are necessary to obtain out-of-plane exchange coupling.…”