It sounds as if you are looking for a 13.3" eInk reader. A quick google search will find the few devices in that size range. The Sony DPT-RP1, the Onyx Max3 and the Onyx Boox Max2Pro are three devices that I can think of off hand. The Sony probably comes closest to your specifications.
As for low magnetic field? I don't think that any ereader has that as a published spec. Given one common phrase in a good majority of the studies on the effect of ELF EMF (0 -3KHz) has been to the effect that "There is no established evidence that ELF EMF is associated with long term health effects" One nice article from the Aussie goverment can be found at
Electromagnetic hypersensitivity.
There was a local to me issue with people who were complaining that the new BC Hydro electrical power meters with their once a month call home for automatic readings were causing symptoms similar to the ones complained about in the referenced article. Oddly, over 70% of the complaints were from people who either had not had the meters installed in their area or the meters had not yet had their RF report home modules enabled.
I tend to regard most of the complaints about ELF EMF sensitivity as being in the same category as the people who suffered from "Chinese restaurant syndrome" blamed on a sensitivity to monosodium glutamate. Considering the amount of glutamic acid/glutamine (2 of the 10 amino acids the human body produces) either free or bound present in the human body runs to about 6000 mg/kg in muscle tissue dropping to ~50mg/l in plasma and that human breast milk contains about 300mg/l of glutamic acid, I found and still find it a trifle hard to believe that it is likely to trigger an allergic reaction.