Q: Does low temperature affect the strength of the magnets (say -40C)?
While high temperatures are well known to have a detrimental impact on Neodymium material, super cold temperatures can actually have the opposite effect.
Most of the Neodymium magnets in the Frenergy catalogue remain fully operational at temperatures up to 80℃. Above this temperature limit, the magnetic properties of the Neodymium material will begin to decline and the overall magnetic strength will be reduced permanently. The decline in power occurs when the heat agitates and disrupts the alignment of the ferromagnetic particles inside the magnetic material.
Once overheating has occurred, the disrupted and misaligned particles are no longer able to maintain the maximum flow of magnetic field that was previously possible. However, at very low temperatures eg. -40℃ the particle alignment is actually enhanced and the flow of the magnetic field between the poles reaches the optimal level which in turn produces more magnetic power.
Gauss readings for a Neodymium magnet in these super cold environments can be slightly stronger than the same magnet in more ambient temperatures. If your application requires a magnet that can tolerate temperatures above 80℃ you can use Neodymium magnets that are specially produced for this purpose. Magnets with an N Grade suffix M can tolerate 100℃. Suffix H can tolerate up to 120℃. Suffix SH for temps up to 150℃. UH suffix for up to 180℃ and EH for up to 200℃