CS-01 Noncollinear Interlayer Exchange Coupling Across IrFe Spacer Layers
Creators: Juliana Lisik
Spencer Myrtle
and Erol Girt
Publisher: name: IEEE
Year: 2025

Antiferromagnetic interlayer exchange coupling between two ferromagnetic layers across a nonmagnetic spacer layer is incorporated into almost all spintronic devices. Recently, we discovered that the coupling angle between two Co layers can be precisely controlled between 0° (ferromagnetic alignment) and 180° (antiferromagnetic alignment) by adding a magnetic material, Fe or Co, to a nonmagnetic Ru spacer layer [1,2]. This is desired, as the optimal design of spintronic devices almost always requires noncollinear alignment between ferromagnetic layers. Ru and Ir spacer layers provide the first and second strongest antiferromagnetic coupling, respectively [3]. For this reason, we built on our RuFe and RuCo work by studying noncollinear coupling between Co layers across IrFe spacer layers [4]. Notably, we achieved the largest antiferromagnetic coupling strength ever observed across spacer layers of 0.6 nm or thicker, with J1 peaking at 3.4 mJ/m2 for Co│Ir50Fe50│Co. The Fe concentration and IrFe thickness regions for which the coupling is ferromagnetic, antiferromagnetic, and noncollinear are shown in Fig. 1(a). Figure 1(c) shows that the noncollinear coupling region of Co│IrFe│Co is significantly larger than that of Co│RuFe│Co or Co│RuCo│Co. The coupling regions after annealing the samples at 350°C for 1 hour, which is typical for device fabrication [5], are shown in Fig. 1(b). The half-filled circles represent samples with a coupling angle of 90° ± 20°, revealing that orthogonal coupling is favoured across the majority of the annealed samples. Moreover, orthogonally-coupled samples with IrFe thicknesses from 0.5 to 0.7 nm and Fe concentrations above 50 at.% have a strong biquadratic coupling strength, with J2 ranging from 1.3 to 3.4 mJ/m2. Since the highest sensitivity of magnetic sensors is achieved through orthogonal alignment of neighbouring magnetic layers, IrFe could enable new designs for sensors.References: [1] Z. R. Nunn, C. Abert, D. Suess, and E. Girt, Sci. Adv., Vol. 6, p.eabd8861 (2020) [2] Z. R. Nunn, J. Lisik, P. Omelchenko, et al., J. Appl. Phys., Vol. 133, p.123901 (2023) [3] S. S. P. Parkin, Phys. Rev. Lett., Vol. 67, p.3598 (1991) [4] J. Lisik, S. Myrtle, and E. Girt, J. Mag. Mag. Mat., Vol. 585, p.171109 (2023) [5] K. Yakushiji, A. Fukushima, H. Kubota, et al., Appl. Phys. Express, Vol. 6, p.113006 (2013)
Antiferromagnetic interlayer exchange coupling between two ferromagnetic layers across a nonmagnetic spacer layer is incorporated into almost all spintronic devices. Recently, we discovered that the coupling angle between two Co layers can be precisely controlled between 0° (ferromagnetic alignment) and 180° (antiferromagnetic alignment) by adding a magnetic material, Fe or Co, to a nonmagnetic Ru spacer layer [1,2]. This is desired, as the optimal design of spintronic devices almost always requires noncollinear alignment between ferromagnetic layers. Ru and Ir spacer layers provide the first and second strongest antiferromagnetic coupling, respectively [3]. For this reason, we built on our RuFe and RuCo work by studying noncollinear coupling between Co layers across IrFe spacer layers [4]. Notably, we achieved the largest antiferromagnetic coupling strength ever observed across spacer layers of 0.6 nm or thicker, with J1 peaking at 3.4 mJ/m2 for Co│Ir50Fe50│Co. The Fe concentration and IrFe thickness regions for which the coupling is ferromagnetic, antiferromagnetic, and noncollinear are shown in Fig. 1(a). Figure 1(c) shows that the noncollinear coupling region of Co│IrFe│Co is significantly larger than that of Co│RuFe│Co or Co│RuCo│Co. The coupling regions after annealing the samples at 350°C for 1 hour, which is typical for device fabrication [5], are shown in Fig. 1(b). The half-filled circles represent samples with a coupling angle of 90° ± 20°, revealing that orthogonal coupling is favoured across the majority of the annealed samples. Moreover, orthogonally-coupled samples with IrFe thicknesses from 0.5 to 0.7 nm and Fe concentrations above 50 at.% have a strong biquadratic coupling strength, with J2 ranging from 1.3 to 3.4 mJ/m2. Since the highest sensitivity of magnetic sensors is achieved through orthogonal alignment of neighbouring magnetic layers, IrFe could enable new designs for sensors.References: [1] Z. R. Nunn, C. Abert, D. Suess, and E. Girt, Sci. Adv., Vol. 6, p.eabd8861 (2020) [2] Z. R. Nunn, J. Lisik, P. Omelchenko, et al., J. Appl. Phys., Vol. 133, p.123901 (2023) [3] S. S. P. Parkin, Phys. Rev. Lett., Vol. 67, p.3598 (1991) [4] J. Lisik, S. Myrtle, and E. Girt, J. Mag. Mag. Mat., Vol. 585, p.171109 (2023) [5] K. Yakushiji, A. Fukushima, H. Kubota, et al., Appl. Phys. Express, Vol. 6, p.113006 (2013)