Hi,
Is it possible to cut in a 60watts CO2 laser a piece of 0,08mm adhesive magnet glued on 3mm DM without affecting the laser?
I have searched here in the forum and have not found anything conclusive.
If I saw a video on Youtube that inspires me confidence that it is possible to do it.
Thanks in advance for your comments. 
Yes, it’s ‘possible’ - its also possible to drink bleach, but not a good idea.
Cutting PVC-based substrates release hydrochloric and hypochlorous acid vapour. It will eat metal, lenses, mirrors, exhaust motors/fans, etc.
Being a strong acid, hydrochloric acid is corrosive to living tissue and to many materials
If you are treating your machine as disposable, go ahead and use it, just be aware that your maintenance intervals will be severely reduced and you will be replacing parts regularly.
And your exhaust is toxic - you can’t just vent that and hope nobody breathes it or that it doesn’t eat anything it shouldn’t.
Alternatively, buy magnetic rubber sheet and apply your chosen substrate to that.
https://www.aliexpress.com/item/32970752121.html
I’ve used this, it cuts fine and you can stick anything to it.
Tech tip: don’t engrave your substrate while it’s on the magnet - engrave, bond, then cut.
Heat will remove the magnetism from the sheet. Cutting is fine - it will be demagnetised only in a small area around the cut line, but engraving will make the magnetic properties disappear, leaving you with expensive rubber sheet 
I use contact spray to bond, but then I do it all the time, have the right sprays on hand and am pretty adept with it. If you are using a light substrate, contact spray can show through in ridges and lines, so you might want to consider a sheet adhesive - it comes with two protection sheets - you peel the sheet, lay your substrate, then process and you end up with easy-peel ‘stickers’ to stick to your magnetic sheet.
https://www.gordonharris.co.nz/product/20338-expression-double-sided-adhesive-sheet-a4-pkt-5
I have been very clear on the subject with your great explanation, thank you. 
I may opt to engrave and cut the pieces and then glue a small neodymium magnet behind it
Thank you, I am aware of the danger of the vapors of certain materials and that one should not let their guard down for wanting to make a couple of cuts on certain materials.
I edited further between your reply - I would/do use rubber magnet sheet. It should be readily available from sign supply houses in Spain, although I had heard AliExpress is quick to deliver to Spain, no?
I have a friend who is an offset printer, and he gives me tons of the stuff - ends of rolls, etc. that is not enough for them to use.
Ask around the printing supplies outlets or signage suppliers.
When folks ask if something is safe to cut, I suggest they look the material up on the internet for the safety information.
Sites like Where to find MSDS and SDS on the Internet
This is also a good read: Laser Cutter Materials - ATXHackerspace - Laser Cutter - Safe Materials - NEVER CUT THESE MATERIALS
Safety first by all means, but if you are only talking about a couple of cuts, then realistically what harm will it do? I had a magnetic plastic sheet that I wanted to install on my 3D printer bed. I had no idea what material it was, but I knew my laser would do the best job of cutting it. So I used the laser to make 2 x 20cm cuts and left the lid down, with the fan running, for 5 minutes after the laser finished. The laser exhausts outside, some 50m away from my neighbours.
It cut it beautifully, there was no smell afterwards, nothing melted inside the laser.
I am seduced by your idea, thank you.
I have bought several types of magnet iron and I’m going to try, very carefully to see what results I get.
Thank you all for your great contributions. 
To check your material for chlorides, cut off a sliver and light it with a flame - if it burns with a green tint, it’s a no-go.
This is a useful chart to burn test plastics against: Burn Test Identification for Plastics | Boedeker