Topic: Sword familiar = Freyr's sword?

[Shiroi Koumori]

I was reading Rick Riordan's Magnus Chase book and I noticed that there is a sentient sword there named sumerbrander aka sword of summer which was also referred to as Freyr/Frey's sword in Norse myth. This magic sword is so good, it fights on its own, but the owner can wield it as well = sword familiar. 

I cannot verify this outside of wikipedia (which did not give a name to the sword) and Riordan's children's book. I have no doubts on Riordan's research since his retelling of Greek/Roman/Egyptian myth is accurate enough. I know more of these 3 mythologies than Norse. But if anyon'e a mythology addict, feel free to verify.

[theplottwist]

I did a little research and, even though the sword did exist in the Norse mythology as Freyr's sentient sword, it really did not have a name. Freyr traded the sword to earn the hand of a giantess, and the lack of this sword will be the cause of his death by the hand of the fire demon Surtr, who is believed to be the new owner of the sword.

There is an hypothesis by Viktor Rydberg that the sword is Lævateinn. Some contest this, tho.