A Persona is basically a person's inner strength/chi manifesting itself into the shape of a creature. There is no external bond. It all comes from within.
In the Persona 3 Club Book, it is explained that shadows are literally fragments of Nyx's psyche, which exist inside of everyone. When people begin to despair or lose hope, their unconscious hold on the "Nyx" that exists within them is weakened, and these fragments can emerge. In order for the psyches of living beings to contain these fragments of Nyx, they were forced to greatly limit their individual lifespans. Because these fragments have been an integral part of life on Earth for so long, the human mind is unable to function without Shadows, which is why those with Apathy Syndrome - people who have lost their Shadows - are merely shells whose minds have broken down.
so you've got a yes and no answer to that. it's something inside of a person but is also something explicitly not native to them, it's coming from an outside source. that said... probably not magic. seems to fall in line a lot more with psychic power.
i'll stand corrected on the evoker bit as a summoning ritual too, can't find anything that says it would be. makes for a very different take from summoning actual demons ala Devil Survivor.
Well, Shadows and Personas are two different things. It's why in 4 you have to defeat your Shadow in order to awaken your Persona.
See this is where I'm getting my info from having played 4, I haven't played 3. But you always had to go into another dimension to battle a possessed version of yourself. Which yes is about inner strength but it's also a magical entity causing the scenario to occur in the first place. ---
I'm bad at Maffs. BEDMAS Bioshock, Earthworm Jim, Diablo 2, Mass Effect 2, Ark: Survival Evolved, Super Meat Boy