you need something like a huge hard drive magnet. i tried with one once and it just was just strong enough to get it off after i played with it for a while.

the easier option is to get a pair of diagonal/wire cutters like these https://www.amazon.com/Crescent-CCA5428-8-Inch-Compound-Diagonal/dp/B00KM0L77I/ref=sr_1_5?keywords=compound+diagonal+cutting+pliers&qid=1581495139&s=hi&sr=1-5

and just snip it off. the ones above (or any similar) cut through the pin like butter. worked great on the pile of jeans i found with tags.

practice first on one of the worst off items until you get how to avoid leaving an abrasion mark on the items.