Multifunctional Magneto-optical Kerr Microscopic Imaging System

Product Introduction

The magneto-optical Kerr microscopic imaging system is based on the self-designed optical path structure, and the optoelectronic components of Olympus and Soleibo; it is used for magnetic domain imaging and dynamics research of magnetic materials/spintronic devices.

Multifunctional Probe Station

With in-plane magnetic field, vertical magnetic field, and multiple pairs of DC/HF probes - the perfect combination of magneto-optical imaging and spin transport testing!
The maximum vertical magnetic field  1.8 T, 1.4 T in-plane magnetic field, 4K-873K variable temperature, can be used for imaging research of hard magnetic materials.

Principle diagram

Multifunctional control system

Test signal control

1. Vertical magnetic field/in-plane magnetic field/current/microwave and other multiple signals, applied synchronously at μs level;
2. The waveform, amplitude, frequency, relative delay and other parameters of each signal can be easily adjusted.

Image processing

1. Real-time subtraction to eliminate background noise;
2. Automatic correction of vibration drift, etc.

Signal analysis

1. Real-time display of current and magnetic field test signals;
2. Based on Kerr image analysis, perform hysteresis loop scanning on the sample locally (220 nm) or globally.

Magnetic Domain Imaging Effects in Perpendicularly Anisotropic Magnetic Films (1 nm Thick)

Magnetic domains on the surface of permanent magnet (NdFeB) bulk

Nanofilm material

Magnetic domains on the surface of silicon steel block

Typical application

Study the properties of magnetic materials

1. Detect the quality of magnetic materials

MgO(sub)/Co/Pt sample: MgO crystal substrate and Co lattice Mismatch-induced film defects.	Poor quality magnetic film, snowflake-like magnetic domains appear during the magnetic reversal process.	High-quality magnetic film with uniform magnetic domain structure and smooth edges.

2. Detect defect location

At the defect, the magnetic domain wall moves and deforms, forming a pinning effect. Using a high-resolution objective lens, the defect position can be directly observed (red circle)

3. Damage detection of spintronic devices

During the microfabrication process of spintronic devices, the edge of the sample is damaged, which leads to a decrease in stability under the action of a magnetic field, and the edge is first flipped.

4. Analyzing the hysteresis loop results

Characterization of Local Magnetic Eigenparameters

Kerr microscopy has a set of methods for characterizing almost all magnetic intrinsic parameters. Compared with other characterization methods, the biggest advantage is that it can perform local property characterization in a small area (220 nm), which can be used for various magnetic control experiments (such as irradiation, voltage control, and optical magnetic control) and materials with inhomogeneous properties characterization.

1. Characterization of the local saturation magnetization M.
Due to dipole interactions, magnetic domain walls repel each other when they come close. By observing the distance of the domain walls under different magnetic fields, the saturation magnetization M of the local region can be extracted. This method was first proposed and verified in 2014 by Professor SNicolas Vernier of the University of Paris-Saclay (the company's technical consultant). It is in good agreement with the VSM measurement results.
 

2. Characterization of local anisotropy energy K.
The hysteresis loop can be obtained by analyzing the light and dark changes of the local Kerr image, so as to extract the equivalent anisotropic field strength in the local area.
 

3. Heisenberg exchange interaction constant Aex.
Using our magnetic field "custom waveform" function to demagnetize the sample by oscillation, and then perform Fourier transform on the obtained maze domain picture, the magnetic domain width can be accurately known, and the Heisenberg exchange interaction stiffness can be extracted.
 

4. Characterization of Dzyaloshinskii-Moriya Interaction (DMI)
Using the asymmetric expansion of the magnetic domain wall under the joint action of the in-plane magnetic field and the vertical magnetic field, the DMI action strength of the thin film material can be measured. Based on the results obtained with this device, the
Table in Nanoscale Magazine.

Magnetic Domain Wall Dynamics Study

1. Measurement of the movement speed of magnetic domain walls under magnetic field, current or other excitations.
method:
Apply a magnetic field/current pulse with an amplitude of B and a width of t, take Kerr images before and after the pulse and make a difference to obtain the domain wall moving distance d, then the velocity v=d/t.
Remark:
The measurement of ultrafast domain wall motion requires ultrashort signal pulses within a limited field of view. The magnetic field with μs response speed configured in this system can realize the measurement of 200 m/s domain wall velocity.

2. Observation of magnetic domain wall tension effect.
Using ultrafast magnetic field pulses in the microsecond range, magnetic bubbles can be created in tiny samples. Using this high-resolution Kerr microscope, the spontaneous shrinkage of magnetic domain walls under their own tension was observed for the first time.

3. Pinning at the Hall bar of the magnetic domain wall.
Using magnetic field pulses, we precisely control the position of the magnetic domain walls in the nanowires. Observe the pinning process of the magnetic domain walls and measure the unpinning magnetic field.

Spin transport property test + imaging

1. Magnetic domain wall motion driven by STT current.
Through the equipped probe and the arbitrary waveform generator of the main control system, a square wave of 50 ns~s level can be applied to the sample, and the magnetic domain wall motion can be observed and the velocity can be measured.

2. Magnetic domain wall motion under the joint action of STT current and vertical magnetic field.
In some materials, purely current-driven domain wall motion cannot be observed. At this time, the ultrafast magnetic field pulse at the μs level of this device can be synchronized with the current to observe the domain wall motion driven by the vertical magnetic field + current, so as to analyze various physical effects, such as the spin polarizability of the heavy metal/ferromagnetic system due to The effect of spin scattering reduction.

3. Magnetic domain wall motion under the joint action of current and in-plane magnetic field.
The Hall spin current interacts with the in-plane magnetic field to induce a magnetic moment flip, the so-called SOT flip. The in-plane magnetic field and electrical test system configured by this equipment can not only realize the electrical test of this process, but also use the synchronization function of the camera and the signal acquisition card to analyze the magnetic domain state corresponding to the flip curve point by point.

4. Introduction to transport testing.
With Keithley 6221 and 2182A source meter, it can measure Hall effect, I-V characteristic (resistivity) and magnetoresistance (MR). With microwave source, microwave probe and lock-in amplifier, etc., ST-FMR and second harmonic test can be performed to characterize the spin-orbit moment of the sample.

Imaging effect

1. 220 nm (100x oil immersion objective) / 450 nm (long working distance objective, tip compatible);
2. Maximum field of view: 1.2 mm×1 mm (5x objective lens);
3. It can detect the magnetic change of 2 atomic layer thin films.

CoFeB(1.3nm)/W(0.2)/CoFeB(0.5) Labyrinth domains in thin films

Image Processing

With any image as the background, real-time subtraction noise image drift correction, automatic addition of scale and other functions.

In CoFeB (20 nm) thin films, (in-plane magnetic field 20 mT) drives magnetic domain switching.	Skyrmion Magnetic Bubbles in W/CoFeB/MgO Thin Films.
SOT-driven magnetic switching in CoTb ferrimagnetic micrometer wires	Domain wall movement driven by (120mT, 5 μs) magnetic field pulses in 200 nm wide Ta/CoFeB/MgO wires.