The use of a piezoelectric force sensor in the magnetic force microscopy of thin permalloy films

•A piezoelectric force sensor is suggested for magnetic force microscopy purposes.•A mechanical force amplifier is used to increase the signal by a factor of 20 to 40.•The theoretical justification of why the amplification has low noise is given.•The force amplitude of 1 pN can be detected in air within a bandwidth of 100 Hz.•Domain magnetic structures in ultrathin nano-island permalloy films are found. A piezoelectric force sensor is suggested for magnetic force microscopy (MFM) purposes. Added between the piezoelectric resonator and the magnetic probe is a mechanical force amplifier in the form of a thin, long resonant arm with an integral micro-rod whereby the amplitude of the force acting on the probe is amplified by a factor of 20 to 40 at a low noise level. When the sensor was operated in air, its noise floor was found to be 1.4 pN (RMS) at a bandwidth of 100 Hz. The piezoelectric sensor requires no repeated calibration; and it is capable of operating in a vacuum, and at cryogenic temperatures. By using this sensor we carried out the MFM of ultrathin (1.5- and 3-nm-thick) Ni79Fe21 permalloy films. The 1.5-nm-thick permalloy films studied have a nanoisland structure, whereas 3-nm-thick ones are contiouous. Domain structures were found in both. The MFM image was found to suffer substantial changes when the external magnetic field was altered by 1 Oe. The structures under study featured both “elastic” and “viscous” magnetic force components.