Between Alnico 5 and Alnico 6, which material has the higher retentivity?

• A. Alnico 5
• B. Alnico 6
• C. Alnico 4
• D. Alnico 3

Answer: (A)

Retentivity is the amount of magnetization a material retains when the external magnetizing field is removed. In Alnico magnets, different grades are heat-treated to tailor how the magnetic domains are arranged and how firmly they stay aligned.

Alnico 5 is designed to develop a microstructure that supports a higher residual magnetization after the field is gone. That means it holds its magnetization better in the absence of an external demagnetizing influence, compared with Alnico 6. The way the domains settle during the heat-treatment of Alnico 5 creates a more stable, less easily demagnetized state, so it ends up with higher retentivity.

Alnico 6, while it may offer other advantages such as certain aspects of coercivity or flux density in specific uses, does not typically provide the same level of retained magnetization as Alnico 5. The other grades mentioned generally have different balances of retentivity and other properties, often yielding lower residual magnetization than Alnico 5 in standard conditions.

So, Alnico 5 has the higher retentivity.