The magnetic domains of SmCo magnets achieve excellent magnetic temperature stability through their unique structure and the pinning effect of magnetic domain walls, enabling stable magnetic performance across a wide temperature range and making them suitable for high-temperature and high-reliability applications.
Definition of Magnetic Domains
Inside magnetic materials (such as iron, cobalt, nickel, and their alloys), there are numerous tiny magnetic regions known as “magnetic domains.” Within each domain, the directions of the magnetic moments are roughly the same.
Still, the magnetic moments of different domains are chaotic when unmagnetized, leading to an overall cancellation of macroscopic magnetism, making the object appear non-magnetic. When the material is magnetized, an external magnetic field gradually aligns the magnetic moment directions of the domains, resulting in a macroscopic magnetic effect.
Effects of Thermal Motion on Magnetic Domains
Once the ordered arrangement of magnetic domains in a magnetized material is disrupted and returns to a chaotic state, the object will lose its magnetism. Heating magnetic materials at high temperatures causes intense irregular motion of internal particles, providing energy for changes in the directions of the domains, which disrupts the originally ordered arrangement and leads to a loss of magnetism. In fact, aside from heating, factors such as intense vibrations and alternating magnetic fields can also disturb the originally ordered particles, causing the magnet to lose its magnetic properties.
The Magnetic Domains of SmCo Magnets
The internal structure of SmCo magnets consists of numerous magnetic domains, where the atomic magnetic moments are neatly arranged, forming tiny magnetic fields. In the unmagnetized state, the directions of the magnetic domains of SmCo magnets are randomly distributed, and their overall magnetism cancels each other out. After magnetization, the domains align along the direction of the external magnetic field, allowing the material to exhibit macroscopic magnetism. This magnetic domain structure is the physical basis for the magnetism of SmCo magnets.
The Pinning Effect of The Magnetic Domains of SmCo Magnets
The magnetic domains of SmCo magnets contain multiple phases, such as the Sm₂Co₁₇ matrix, SmCo₅ unit walls, and Z phases. The interfaces of these phases form a complex network of magnetic domain walls that effectively pin the walls, impeding their movement during temperature changes. For instance, the interface between SmCo₅ cell walls and the Z phase with the Sm₂Co₁₇ matrix can fix the domain walls through mechanisms such as curl instability or interfacial characteristics, making it difficult for domains to undergo significant changes during temperature fluctuations, thus maintaining magnetic stability.
Temperature Effects on The Magnetic Domains of SmCo Magnets
| Reversible Temperature Changes: Within a certain temperature range, the positions and sizes of magnetic domain walls in SmCo magnets may slightly adjust with temperature changes, but the overall direction of domain arrangement remains essentially unchanged. This is due to the strong magnetic anisotropy of SmCo, which can resist thermal motion disturbances caused by temperature changes. The small temperature coefficient (e.g., αbr ≈ -0.035%/℃) indicates that the magnetic performance varies only slightly with temperature.
| Irreversible Temperature Changes: When the temperature exceeds the maximum operating temperature (usually between 250-350℃), the domain walls may overcome the pinning constraints and undergo irreversible movement or domain merging, leading to a decline in magnetic performance. However, SmCo has a relatively high temperature (725-850℃), providing a considerable safety temperature range for practical applications.
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