Abstract
Perpendicular magnetic anisotropy (PMA) is an essential condition for CoFe thin films used in magnetic random access memories. Until recently, interfacial PMA was mainly known to occur in materials stacks with MgO\CoFe(B) interfaces or using an adjacent crystalline heavy metal film. Here, PMA is reported in a CoFeB\Ta bilayer deposited on amorphous high-κ dielectric (relative permittivity κ=20) HfO2, grown by atomic layer deposition (ALD). PMA with interfacial anisotropy energy Ki up to 0.49 mJ/m2 appears after annealing the stacks between 200°C and 350°C, as shown with vibrating sample magnetometry. Transmission electron microscopy shows that the decrease of PMA starting from 350°C coincides with the onset of interdiffusion in the materials. High-κ dielectrics are potential enablers for giant voltage control of magnetic anisotropy (VCMA). The absence of VCMA in these experiments is ascribed to a 0.6 nm thick magnetic dead layer between HfO2 and CoFeB. The results show PMA can be easily obtained on ALD high-κ dielectrics.
Highlights
Perpendicular magnetic anisotropy materials are key enablers for spintronics and high retention magnetic random access memory technologies
Thin films composed of Co, Fe and B have been thoroughly investigated and, adjacent to suitable materials, display PMA when they are sufficiently thin.[1,2]
Ferromagnetic thin films deposited on amorphous oxides like thermally grown SiO2 can show PMA.[9]
Summary
Perpendicular magnetic anisotropy materials are key enablers for spintronics and high retention magnetic random access memory technologies. The HfO2 is likely amorphous as deposited[15] and the monoclinic (11-1) peak at 28.2◦17 appears after the in situ measurement (i.e. annealing at 1000◦C: not shown, outside of the in situ 2θ window). Boron outdiffusion upon annealing a CoFeB thin film is expected,[18,19] and likely leads to crystalline reordering of CoFe as well as a thickness increase in the Ta layer[19] adjacent to the CoFeB.
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