Element-Specific Magnetic Properties of Di-Erbium Er2@C82 and Er2C2@C82 Metallofullerenes: A Synchrotron Soft X-ray Magnetic Circular Dichroism Study (Element-specific magnetic properties of Di-erbium Er2@C 82 and Er2C2@C82 metallofullerenes: A synchrotron soft X-ray magnetic circular dichroism study)