I have searched where I can, and can find no obituary/bio for the Magnus that is buried in Deer Creek, MN. I do extensive research for that area. I know the cemetery well, and I don't believe there is even a headstone/footstone/marker of any kind for him, nor are there any other Sederbergs in either of the Deer Creek Cemeteries (Or Otter Tail County, for that matter). It appears what little information we have, is from the Otter Tail County Historical Society, so you may want to contact them and see what they may have to offer!https://www.otchs.org/index.html
Sorry I wasn't of much other help, but i will keep this name in mind when I'm down there next!