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Variable Magnetic Field Generator Nanosurf's Innovative Design
The Variable Magnetic Field Sample Holder (VMFSH) is a specialized accessory designed for use with Nanosurf’s CoreAFM, FlexAFM, and DriveAFM systems. This advanced tool facilitates atomic force microscopy (AFM) measurements under a variable in-plane magnetic field, enabling detailed studies of magnetic materials at the nanoscale.
The Significance of Magnetic Materials
Magnetic materials play a crucial role in modern science and technology, featuring prominently in applications ranging from household electronics to advanced medical diagnostic tools. As technology continues to miniaturize, these materials are f inding new applications in areas such as data storage, memory devices, spintronics, robotics, electronics, and biomedical devices.
To advance the understanding and development of magnetic (nano)materials, nanoscale characterization is essential. The VMFSH, when combined with standard or advanced AFM modes, allows for correlative measurements under varying magnetic fields. This capability makes it possible to observe changes in magnetization, conductivity, and topography in situ, using magnetic fields up to 720 mT.
Understanding Magnetic Hysteresis
The VMFSH is particularly suited for studying ferrimagnets and ferromagnets, which are widely known for their ability to retain memory of an applied magnetic field even after its removal. Magnetic hysteresis—the variation of magnetization properties depending on whether the magnetic field is increasing or decreasing—is a key focus of such studies.
In ferromagnets, high magnetic fields align magnetic domains, leading to saturation magnetization. When the field reverses, domain alignment is disrupted, but residual magnetization remains at zero field. To fully demagnetize the material, a coercive f ield (Hc) is applied, canceling out net domain alignment. The behavior of domains near the coercive field is particularly interesting, as they often form structuredpatterns influenced by material properties such as grain size, stress, and temperature. These properties can be precisely probed using AFM.
Magnetic Hysteresis Loop of a Ferromagnet
Figure 1. Magnetic hysteresis loop of a ferromagnet. Mg-residual magnetization, He- coercive field. At high fields the magnetic domains are fully aligned. At intermediate fields, the domains align patterns reducing the magnetization strength.
Innovative Design of the VMFSH
The VMFSH (Fig. 2) employs a stack of permanent magnets within the sample holder base to generate the magnetic field. These magnets are rotated by a programmable stepper motor, producing a variable in-plane magnetic field up to 720 mT (7200 G). When the magnets’ poles are aligned, the field reaches its maximum strength, while alignment at 90° produces a zero-field state (Fig. 3). The field is concentrated around the sample via ferromagnetic poles.
Unlike solenoid magnets, the use of permanent magnets eliminates heat dissipation f luctuations, ensuring minimal thermal drift and consistent performance.
The Variable Magnetic Field Sample Holder
Figure 2. The variable magnetic field sample holder. The base contains the permanent magnets, a precise stepper motor for their rotation, and an integrated calibrated Hall sensor. The sample mounting plate is positioned in the center of the top plate, between the magnetic poles.
Working Principle of the Variable Magnetic Field Sample Holder
Figure 3. Working principle of the variable magnetic field sample holder. The permanent magnets in the base of the holder can rotate around the vertical axis. When the magnetic field of the magnets is aligned with the magnetic poles, the field is at its maximum (left image), and when the magnetic field of the magnets is normal to the poles, the field is zero (right image).
Field Adjustability
The field strength can be adjusted by controlling the magnet rotation and the gap width between the magnetic poles. Five spacers are provided to define these gaps, offering spacings of 2, 4, 6, 8, or 10 mm, corresponding to maximum fields of 720, 370, 240, 180, and 140 mT, respectively. A Hall sensor integrated into the system ensures accurate field measurements.
Automation and Precision
The VMFSH is equipped with automation software that allows precise control over the magnetic field. Users can set specific field setpoints and conduct Magnetic Force Microscopy (MFM) scan series within a defined field range. The automated resolution for field adjustment is 0.1 mT, while manual adjustments achieve an even finer resolution of 0.005 mT.
Applications in Advanced Research
The VMFSH is compatible with advanced AFM modes, such as Conductive AFM and MFM. For example, it has been used to study Shakti spin ice configurations—a nanometer-scale arrangement of magnets. By imaging these lattices at various magnetic states, researchers gain insights into magnetic behavior during reversal processes (e.g., at-200 mT and-10 mT, as shown in Fig. 4).
MFM images of Shakti Spin Ice Structure
Figure 4. MFM images (5 x 5 mm2) of Shakti spin ice structure made at different magnetic fields imaged using the variable magnetic field sample holder using the CoreAFM.
Key Features
Innovative Permanent Magnet Design:
Eliminates thermal drift common in solenoid magnets.Integrated Hall Sensor:
Ensures precise magnetic field measurement.ProgrammableStepper Motor:
Enablesfieldvariation with 0.1 mT resolution.HighMaximumFieldStrength:
Supportsfields upto720mT.
The VMFSH’s unique design and capabilities make it an indispensable tool for researchers exploring the nanoscale properties of magnetic materials, enabling groundbreaking discoveries across multiple scientific disciplines.
Specifications Of The Variable Magnetic Field Sample Holder
| Features | Variable in-plane magnetic field generator; Integrated hall sensor. |
| Platform compatibility | CoreAFM, FlexAFM, DriveAFM |
| Requirements | Accessory Interface, Isostage 300 |
| Sample size | 2 x 2 mm2 to 10 x 10 mm2 |
| Maximum field | 720 mT (7200 G), 2 mm gap |
| Field resolution | 0.1 mT (1G) |
| Magnetic field | Permanent rare earth magnets |
| Field variation | Programmable stepper motor |
| Dimensions | 100 mm x 140 mm |
Conclusion
The Variable Magnetic Field Sample Holder (VMFSH) is a cutting-edge accessory that enhances the capabilities of atomic force microscopy by enabling precise measurements in a variable in-plane magnetic field. Its innovative design, featuring permanent magnets, programmable field adjustments, and advanced automation, makes it a powerful tool for nanoscale research. By offering unprecedented accuracy and flexibility, the VMFSH empowers scientists to investigate magnetic materials with remarkable depth, advancing applications in data storage, spintronics, biomedical devices, and beyond. For researchers focused on the complexities of magnetic hysteresis and domain behavior, the VMFSH provides an invaluable platform to drive innovation and deepen understanding in this critical field.