Since most of Earth's shielding comes from mass (the atmosphere), and life still continues with no major mass exctinctions even during pole reversals when the magnetic field is a fraction of its normal strength, I'd say the case is made that mass works quite well. It need not even rotate with the station, in fact it's easier if it doesn't-- a shell filled with slag, mine tailings or regolith can do the job quite well.

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort