Related Experiment Video
Updated: Jun 9, 2025
08:55
Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
8.5K
Grain alignment in hexaferrite permanent magnets by compaction at room and elevated temperatures
Jacob L Valentin1, Frederik H Gjørup1,2, Cecilie G Knudsen1
1Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Denmark. mch@chem.au.dk.
Nanoscale
|October 28, 2024
Summary
Hot compaction significantly improves grain alignment and magnetic properties in strontium hexaferrite permanent magnets. This method enhances density and texture strength compared to cold compaction, overcoming magnetic short-circuiting issues.
Area of Science:
- Materials Science
- Solid State Physics
- Magnetism
Background:
- Strontium hexaferrite (SrFe12O19) is a key permanent magnet material.
- Achieving high performance requires controlled grain alignment (texture).
- Applied magnetic fields are typically used to induce grain alignment.
Purpose of the Study:
- To investigate shape-controlled precursors for grain alignment in strontium hexaferrite without an external magnetic field.
- To compare the effectiveness of cold and hot compaction methods on texture and magnetic properties.
- To understand the role of magnetic short-circuiting in grain alignment during compaction.
Main Methods:
- Four compaction series: cold pressing (CP), cold pressing followed by sintering (CPS), spark plasma sintering (SPS), and induction pressing (IP).
- Experiments conducted below and above the Curie temperature to assess magnetic interactions.
- Characterization of texture (grain alignment) and remanent magnetization.
Main Results:
- Hot compaction methods (SPS, IP) yielded significantly sharper textures and higher remanent magnetization compared to cold compaction (CP, CPS).
- Bulk density nearly doubled in hot compacted samples versus cold compacted ones.
- Cold compaction showed weaker texture and lower magnetization, attributed to inter-particle magnetic short-circuiting.
Conclusions:
- Hot compaction is superior to cold compaction for producing high-performance strontium hexaferrite magnets.
- Shape-controlled precursors and hot compaction enable effective grain alignment without applied magnetic fields.
- Minimizing magnetic short-circuiting is crucial for achieving strong texture and magnetic properties.
Related Concept Videos
01:31Ferromagnetism
2.4K
Materials like iron, nickel, and cobalt consist of magnetic domains, within which the magnetic dipoles are arranged parallel to each other. The magnetic dipoles are rigidly aligned in the same direction within a domain by quantum mechanical coupling among the atoms. This coupling is so strong that even thermal agitation at room temperature cannot break it. The result is that each domain has a net dipole moment. However, some materials have weaker coupling, and are ferromagnetic at lower...
2.4K
01:23Atomic Nuclei: Nuclear Relaxation Processes
632
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis.
632