Ppp mfmr

The X-ray diffraction (XRD) patterns of these films were recorded by a Bruker D8 diffractometer at a scanning rate of 2° min⁻¹, under Cu-K_α radiation (λ = 1.5418 Å). Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were performed using a HITACHI S5000 with an energy-dispersive analysis system, Bruker XFlash 6|60. DC magnetization measurements were performed on a Superconducting Quantum Design (SQUID) magnetometer (MPMS-XL). The SQUID measurements of the magnetization of samples as a function of the magnetic field were carried out at 300 K in fields between −2000 Oe and +2000 Oe. Film surface morphologies were examined by atomic force microscopy (AFM) under tapping mode (Asylum Research). The Cypher AFM/MFM manufactured by Asylum Research was performed for MFM experiments. The MFM tips used were PPP-MFMR from NANOSENSORS with 300 Oe coercivity, 300 emμ cm⁻³ magnetic moment, and magnetic resolution better than 50 nm, optimized for non-perturbative magnetic imaging with high spatial resolution.

A series of ML-MFM probes were fabricated using magnetron sputtering (AJA International Aurora, ATC-2200) in Ar atmosphere. Commercial Si cantilevers (PPP-FMR, Nanosensors™) with typical resonance frequency f₀ = 70–80 kHz, force constant = 2–3 Nm⁻¹ and curvature radius of ~10 nm were chosen for coating. The coating was deposited on two faces of the pyramidal probe (Fig. 2a) and the ML-MFM probe was comprised of two Co layers separated by a Si interlayer (Fig. 1b). Two coating thicknesses were considered, i.e., Co(30 nm)/Si(10 nm)/Co(30 nm) for thick and Co(15 nm)/Si(10 nm)/Co(15 nm) for thin ML-MFM probe. The film thicknesses were estimated using SEM and material deposition rates measured on a flat surface. The final curvature radii were ~20 nm and ~35 nm for thin and thick ML-MFM probes respectively. For comparison, the curvature radius of commercial MFM probes (PPP-MFMR, Nanosensors™²⁵ ) is ~30 nm. Detailed SEM investigations of custom-made ML-MFM probes revealed that the outer magnetic layer is longer, i.e., geometrically closer to the sample’s surface, than the inner one, see schematics in Fig. 1b. Furthermore, the orientation of the ML-MFM probe faces was within 2° of being perpendicular to the sample surface during scanning.

MFM measurements were performed by a Nanosurf Flex-AFM with C3000 controller in tapping/lift mode with a lift height of 80 nm, a peak-to-peak amplitude of 80 nm and a pixel size of 20 nm. These settings were chosen from preliminary experiments as a trade-off between lateral charge-contrast resolution and minimal signal overlap from the sample topography. Additionally, an SIS ULTRAObjective in non-contact/lift mode with a lift height of 100 nm and a pixel size of 200 nm was applied for the MFM measurements. Hard magnetic MFM probes (Nanosensors PPP-MFMR) with a nominal resonance frequency of 70 kHz and a spring constant of 2.8 N·m⁻¹ were employed.