sterling 925 silver means there is still 7.5 % of another metal that may cause the slight tug by a magnet. unless the silver is mixed with a metal like brass or aluminum you know, something that does not attract to a magnet. so depending on the the metals mix in your silver and magnet size you can get a slight tug....thats my best guess
No, a magnet will not stick to sterling silver. However, just because the magnet does not stick to sterling silver, it is not a guarantee of the item’s silver authenticity. This is only one type of test to determine authenticity but it is not always accurate so this is only a secondary test.
Testing the authenticity of sterling silver, is usually done through the use of magnets. It is said by jewelery experts that authentic sterling will not attract magnets. Keep in mind however, that your sterling can be real, but have other alloys mixed into it, thereby causing a slight magnetic attraction.