Entwicklung eins metrologischen Magnetkraft-Mikroskops mit großem Rasterbereich

In the frame of the European Metrology Programme for Innovation and Research (EMPIR) and within the project “Nanoscale traceable magnetic field measurements (NanoMag)”, a unique metrological large-range magnetic force microscopy (Met. LR-MFM) has been recently realized jointly by the precision engineering and electricity divisions at PTB. The MFM is a kind of widely applied technique for measuring nanoscale magnetic stray fields with a spatial resolution down to 10 nm or even below. However, today conventional MFM measurements are usually qualitative only and lack accuracy due to insufficient dimensional measurement accuracy as well as the challenge in interpreting the measured MFM data. Additionally, commercial MFMs available so far have a limited measurement range, typically of tens of micrometer. The development of the Met. LR-AFM thus directly addresses the challenging needs.

Some unique features are realised in the Met. LR-MFM. In its design, the scanner motion is measured by using three laser interferometers along the x, y, and z axes. Thus, the scanner position and the lift height of the MFM can be accurately and traceably determined with sub-nanometre accuracy, allowing accurate and traceable dimensional measurements. The Met. LR-MFM has a measurement range of 25 mm x 25 mm x 5 mm, larger than conventional MFMs by almost three orders of magnitude. It is capable of measuring samples from the nanoscale to the macroscale, and thus, it has the potential to bridge different magnetic field measurement tools having different spatially resolved scales, for instance, Hall sensors, Magneto Resistance (MR) sensors and Magneto Optical Indicator Films (MOIF). Three different measurement strategies referred to as Topo&MFM, MFMXY, and MFMZ have been developed. The Topo&MFM mode is designed for measuring topography and MFM phase images, similar to conventional MFMs. The MFMXY mode differs from the Topo&MFM as it measures topography only during the first line, thus reducing tip wear and saving measurement time. The MFMZ mode allows the imaging of the magnetic stray field in the xz- or yz-planes.

A number of measurement examples on a reference multilayered thin film sample made of [Co(0.4nm)/Pt(0.9nm)]100*) and on a patterned magnetic multilayer [Co(0.4nm)/Pt(0.9nm)]10*) with stripes with 9.9 μm line width and 20 μm periodicity (as illustrated in Fig.1) were carried out, indicating the excellent measurement performance of the developed instrument.



Fig.1 Demonstration of a large range MFM measurement, shown as (a) an MFM phase image measured on a patterned magnetic multilayer sample over an area of 204.7 µm x 51.1 µm (x,y); (b) a cross-sectional profile at the marked line in (a) and an illustration of the cross-section of the patterned structure, and (c) a zoom-In MFM phase image measured over an area of 15.33 µm x 15.33 µm marked as the dashed square in (a).

*) 100 or 10 as index means 100 or 10 layers, respectively

Reference:

[1] Gaoliang Dai, Xiukun Hu, Sibylle Sievers et al. 2018 Metrological large range magnetic force microscopy, Rev. Sci. Instrum. 89, pp. 093703