Determining a magnet's life?

[Terry Pinnell]

I've been pleased with this pair of 'magnetic' sandals I bought a
couple of summers ago. I just slip a foot into one, shake it a bit if
necessary, and the pair of magnets mounted in its strap automatically
fastens it securely with a sharp snap.

Anyone know the approximate 'life' of such magnets? Are we talking
decades, centuries or millennia?

--
Terry Pinnell
Hobbyist, West Sussex, UK

 

[Robert Baer]

Terry Pinnell wrote:

I've been pleased with this pair of 'magnetic' sandals I bought a
couple of summers ago. I just slip a foot into one, shake it a bit if
necessary, and the pair of magnets mounted in its strap automatically
fastens it securely with a sharp snap.

Anyone know the approximate 'life' of such magnets? Are we talking
decades, centuries or millennia?

--
Terry Pinnell
Hobbyist, West Sussex, UK

Depends on the formulation.
Older ("first" generation) Alnicos were a bit "soft" and certain
storage conditions could make them lose some of their magnetization in a
few years.
AFAIK all new Alnicos and rare-earth types will last until they get
heated to or above their Curie point.
The "plastic" magnets are very wimpy and canot be trusted...