Zhizhen Precision Instrument (Qingdao) Co., Ltd.

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Multi-Purpose High-Resolution Magneto-Optical Kerr Microscopy Imaging System

+86-13335086685 Yao Jingli

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Magnetic Measuring Instruments

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Product Description
Technical Indicators
Applications

Product Model:

KMP-S

Equipment Description:

This equipment is designed based on our independently designed optical pathway, and Olympus and Thorlabs photonic components for magnetic domain imaging and dynamic studies of magnetic materials/spintronic devices.

Multi-Functional Probe Station:

● Our multi-functional probe station provides in-plane and perpendicular magnetic fields and seamlessly integrates with multiple pairs of DC/RF probes for magneto-optical imaging and spintronic transport testing.

● With a maximum 1.4 T perpendicular magnetic field, 1 T in-plane magnetic field, and a temperature range from 4.2 K to 835 K, it is ideal for imaging research on hard magnetic materials.

Main Functions:

Imaging Effect:

● 225 nm (100x oil immersion objective)/450 nm (long working distance objective, compatible with

● Maximum field of view: 1.9 mm × 1.1 mm (5x objective)

It can detect magnetic variations in three atomic layers of film

CoFeB (1.3 nm)/W (0.2)/CoFeB (0.5)

Maze domains within the film

Image Processing:

Functions, like real-time differencing, noise elimination, image drift correction, and automatic addition of scale, are all available with any image as the background.


● In CoFeB (20 nm) thin film, magnetic domain reversal is achieved with [an in-plane magnetic field of 20 mT].	● Skyrmion magnetic bubbles in W/CoFeB/MgO films

Magnetic reversal driven by SOT in CoTb ferromagnetic microwires

Domain wall motion driven by [120 mT, 5 μs] magnetic field pulses in 200 nm-wide Ta/CoFeB/MgO wires

Magnetic Field Probe Station:

● In-plane magnetic field: ≤1 T, real-time magnetic field detection resolution of 50 µT

● Three-axis orthogonal magnet switching:

Magnetic field 1: ≤1.4 T

Magnetic field 2: ≤30 mT; rise time: 100 µs

Magnetic field 3: maximum magnetic field ≥60 mT; rise time: 0.5 µs

● Up to 4 DC/RF probes can be configured, and it is compatible with 6221/2182 instruments, and suitable for electrical transport testing. It is also equipped with transport and in-situ imaging synchronization software.

Other Functions:

● Hysteresis loops can be obtained through analyzing global or local (225 nm) images.

● The hysteresis loop’s horizontal axis can be driven by in-plane, perpendicular magnetic fields, or current signals.

● A variable temperature system ranging from 4.2 K to 835 K can be configured.

● It is designed with magneto-resistance measurement and other transport testing systems and software.

● Various interfaces are reserved for user-customized modifications based on experimental requirements.

Applications

① Study Magnetic Material Properties

1. Detect Magnetic Material Quality

MgO(sub)/Co/Pt Sample: Defects in the film caused by the mismatch between the MgO crystal substrate and the Co lattice.

Magnetic films with poor quality exhibit snowflake-like magnetic domains during the magnetic reversal process.

High-quality magnetic films display uniform magnetic domain structures with smooth edges.

2. Detect Defect Location

At the site of a defect, deformation occurs in the motion of magnetic domain walls, resulting in a pinning effect. The defect location can be directly observed through a high-resolution objective (highlighted in red circles).

3. Spintronic Device Damage Detection

During the microfabrication of spintronic devices, damage often arises at the sample edges, resulting in reduced stability under magnetic field influence, and initial reversal at the edges ^[1].

4. Hysteresis Loop Result Analysis

The magneto-optical Kerr microscope, with the spatial resolution advantage, can analyze the magnetic domain states corresponding to the hysteresis loop. As shown in the left image, the sample experiences spontaneous demagnetization due to the dominance of dipolar interactions over anisotropy.

[1] Yu Zhang et al. Phys. Rev. Appl. 9,064027(2018).

[2] Xueying Zhang et al., Advanced Science 8,2004645(2021).

② Typical Application—Local Magnetic Intrinsic Parameter Characterization

The Kerr microscope offers a comprehensive method for characterizing nearly all intrinsic magnetic parameters. Its key advantage over other characterization methods is that it can characterize local properties within small areas (220 nm), making it possible to characterize a range of magnetic manipulation experiments (including irradiation, pressure control, and light-induced magnetism), and characterize diverse heterogeneous materials.

● Local Saturation Magnetization MS Characterization

Magnetic domain walls repel each other when in close proximity due to dipolar interactions. By observing the distance between domain walls under different magnetic fields, the local saturation magnetization MS can be extracted. This method was initially proposed and validated by Prof. Nicolas Vernier, a technical consultant of our company, at Université Paris-Saclay in 2014, and the results got through it align well with VSM measurement results ^[1].

● Characterization of Local Anisotropy Constant K

The hysteresis loop can be obtained by analyzing the local Kerr images’ contrast variations and thereby, the local equivalent anisotropy field strength extracted.

● Heisenberg Exchange Constant A_ex

The precise magnetic domain width can be measured by oscillating and demagnetizing the sample and subsequently performing a Fourier transform on the resulting labyrinth domain images, and on this basis, the Heisenberg exchange stiffness obtained ^[2].

For this measurement, prior knowledge of the sample’s saturation magnetization and anisotropy is necessary, which can be obtained through vibrating sample magnetometer measurements.

Magnetic domain structure of demagnetized film materials

● Characterization of Dzyaloshinskii-Moriya Interaction (DMI)

Our equipment measures the strength of DMI in film materials through the asymmetric expansion of magnetic domain walls under the combined influence of in-plane and perpendicular magnetic fields. The results obtained using this equipment have been published in the Nanoscale journal ^[3].

[1] N. Vernier et al., Appl. Phys. Lett. 104,122404(2014).

[2] M. Yamanouchi et al., IEEE Magn. Lett. 2,3000304(2011).

[3] Anni Cao et al., Nanoscale 10,12062(2018).

③ Research on Magnetic Domain Wall Dynamics

1. Measurement of Magnetic Domain Wall Velocity Under the Influence of Magnetic Fields, Current, or Other Excitations

Methods:

Capture Kerr images are captured before and after applying a magnetic field/current pulse with an amplitude of B and a width of t. The difference between these images provides the domain wall motion distance, d, and then, the velocity, v = d/t is obtained.

Remarks:

To measure the ultrafast domain wall motion within a limited field of view, ultra-short signal pulses are essential. Our system features a magnetic field with a microsecond-level (μs) response time, facilitating measurements of domain wall velocities up to 200 m/s.

10 ms square wave magnetic field pulse

4 μs ultrafast magnetic field pulse

2. Observation of Magnetic Domain Wall Tension Effect

Magnetic bubbles can be produced within tiny samples by applying microsecond-level ultrafast magnetic field pulses. With the aid of this high-resolution Kerr microscope, the spontaneous contraction process of magnetic domain walls under their own tension has been observed for the first time ^[1-3].

3. Magnetic Domain Wall Pinning in Hall Bar

We accurately control the positioning of magnetic domain walls within nanowires using magnetic field pulses. Through this, we observe the pinning process of the magnetic domain wall and measure the depinning field ^[1].

[1] Xueying Zhang et al., Phys. Rev. Appl. 9,024032(2018).

[2] Xueying Zhang et al. Nanotechnology 29,365502(2018).

[3] Anni Cao et al., IEEE Magn. Lett. 9,1(2018).

④ Spintronic Transport Property Testing + Imaging

1. STT Current-Driven Magnetic Domain Wall Motion

With the aid of the probes and the arbitrary waveform generators of the master control system, square waves can be applied to the sample at levels ranging from 50 nanoseconds to seconds, and then, the magnetic domain wall motion observed and velocity measured.

2. STT-Induced Magnetic Domain Wall Motion Under the Combined Action of Current and Vertical Magnetic Field

In certain materials, pure current-driven magnetic domain wall motion cannot be observed. In such cases, the equipment can synchronize microsecond-level ultrafast magnetic field pulses with the current. On this basis, the domain wall motion driven by both vertical magnetic fields and the current can be observed, and various physical effects analyzed, such as the reduction in spin polarization rates in heavy metal/ferromagnetic systems due to spin scattering effects ^[1].

Microsecond-level synchronized magnetic field and current square wave pulses

3. Magnetic Domain Wall Motion Under the Combined Action of Current and In-Plane Magnetic Field

The combined action of the Hall spin current and in-plane magnetic field induces magnetic moment reversal, known as the SOT reversal. Our equipment is equipped with an in-plane magnetic field and an electrical testing system. This system can either perform electrical testing of this process, or make point-by-point analysis of the magnetic domain states corresponding to the reversal curve using synchronized camera and signal acquisition card functions ^[2].

4. Transport Testing Overview

When used together with the Keithley 6221 and 2182A source meters, our system can measure the Hall effect, I-V characteristics (resistivity), and magnetoresistance (MR). Additionally, when supported by a microwave source, microwave probe, and lock-in amplifier, it can finish ST-FMR and second harmonic tests, realizing the characterization of the sample’s spin-orbit torque magnitude.

[1] Xueying Zhang et al., Phys. Rev. Appl. 11,054041(2019).

[2] Xiaoxuan Zhao et al., Nanotechnology 30,335707(2019).