UNIST Professor Jiyoon Kim's team, Seoul National University Professor Minsang Kwon's team
Development of magnetic smart materials with redesignable magnetization patterns
Prospects for application in biomedical engineering, flexible devices, soft robots, etc.


It has become possible to create more diverse shapes of magnetic smart materials that move on their own in response to a magnetic field.

On the 3rd, Professor Jiyoon Kim's research team from the Department of Materials Science and Engineering at UNIST announced that they had developed a magnetic smart material that can change its magnetization pattern in collaboration with Professor Minsang Kwon's research team from the Department of Materials Science and Engineering at Seoul National University.

Magnetic smart materials move through the interaction between the magnetization pattern pre-input inside and the external magnetic field. It utilizes the attractive or repulsive force that occurs when another magnet (magnetic field) is placed on a magnet. The magnetization pattern is a blueprint that determines the strength of the magnetic force and the direction of the N/S pole. Depending on the magnetization pattern, the magnetic smart material bends or folds in a specific direction.

However, once the magnetization pattern is fixed during the material production process, it is not easy to change. This is the reason why magnetic smart materials are not widely used despite their advantages of being able to remotely control movement and responding quickly to external stimuli. The joint research team solved this problem by using a material that changes state depending on temperature.

The developed material has a structure in which micrometer (10 ^-6 m)-sized granules (magnetic microspheres) containing a mixture of magnetic particles (magnetic material) and a phase change material (polyethylene glycol; PEG) are embedded in a polymer matrix. Because PEG is a phase change material that changes from solid to liquid, it is possible to repeatedly change the magnetization pattern.

Just as a bead in ice is firmly fixed but moves freely in water, the magnetic particles can use an external magnetic field to input a new magnetization pattern because of the phase change material that has become liquid. On the other hand, when the temperature drops to room temperature, the magnetic particles cannot physically move because of the phase change material that has become solid, so the magnetization pattern is fixed.

“The solid-liquid phase change of PEG is a reversible reaction, so the magnetization pattern of soft composite materials can be easily redesigned as much as desired simply by repeating the above process,” explained Song Hyeon-seo, the first author and a researcher in the combined master’s and doctoral program in the School of Materials Science and Engineering at UNIST.

The research team also developed a magnetic soft actuator capable of self-folding paper using the developed composite material. The magnetization shape of the actuator was redesigned in situ in an actual operating environment, and various complex three-dimensional shapes were realized by exposing it to a magnetic field. Since it utilizes a reversible reaction, it has the advantage of maintaining the material's performance even if a new magnetization form is repeatedly input to the same actuator.

Professor Kim Ji-yoon explained, “Unlike previous studies, the significance of this study lies in the fact that we have developed a material whose magnetization form can be easily redesigned without changing the inherent characteristics of the magnetic particles or polymer substrate.” He continued, “The material developed this time is also flexible, and will play a role in various fields that require variable-structure smart materials, such as biomedical engineering, flexible electrical devices, and soft robots.”

Meanwhile, this study (Reprogrammable Ferromagnetic Domains for Reconfigurable Soft Magnetic Actuators) was published on July 8 in the prestigious journal in the nano field, Nano Letters. The research was conducted with the support of the National Research Foundation of Korea and the Korea Institute of Industrial Technology Evaluation and Planning.