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For real-world applications, it is desirable to realize field-free spin–orbit torque (SOT) switching in thin films with high perpendicular magnetic anisotropy (PMA). In this paper, we report that field-free SOT switching in a L10-FePt single layer with a large switching ratio of 26% is obtained by using a MgO ⟨100⟩⋀8°/⟨100⟩ miscut substrate. It is found that field-free switching depends on the direction of the imposed pulse current. Only when the electric current is along the y (010)-direction but not along the x (100)-direction does field-free switching happen, which can be attributed to the tilted PMA induced symmetry breaking in the x–z plane. Furthermore, under the field-free condition, our FePt single layer system exhibits stable multi-state magnetic switching behavior and nonlinear synaptic characteristics. This work paves the way to realize field-free SOT switching in the L10-FePt single layer, which will have significant impact on spin memory devices and synaptic electronics.

FePt (10, 20, 40, and 60 nm) films were fabricated on four different single crystal substrates [MgO (001), KTaO3 (001), SrTiO3 (001), and LaAlO3 (001)], and the effects of lattice mismatch on the microstructure and magnetic properties of FePt films were systematically investigated. The X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) results showed that the different lattice mismatch between the substrates and FePt films resulted in the different crystallographic texture and microstructure of the FePt films. Under the tensile strain between the FePt and substrates (MgO, KTaO3, SrTiO3), the FePt films preferred to form L10 FePt (001) texture. The perpendicular anisotropy of the FePt films grown on MgO was larger than that grown on KTaO3 and SrTiO3. For the FePt films grown on the LaAlO3 substrate, both FePt (110) and (001) orientations were found, which indicated the presence of tensile and compressive strain, respectively. With the reduction of the lattice mismatch between the FePt (10 nm) and substrate from 5.8% (MgO) to 2.4% (KTaO3), and 0.1% (SrTiO3), the microstructure of the FePt films changed gradually from granular to continuous films (SEM and TEM results). The microstructure of the 10 nm FePt film grown on LaAlO3 substrate showed granular structure.