Intellectual property generally refers to tangible creative material, not thoughts per se.
Consequently, you might assert IP rights over an employee's work product (notes from research, for example), or some more finished result (e.g. a specific essay), but you have no property right to the intern's own thought process or the conclusions they draw from their activities, regardless of whether you compensate them for the work during which time (you assert) they were also thinking. You do not say whether the intern's published essay was written while performing employee work for you (e.g. on 'your' time), but I assume it was written later.
As Barbara Punt points out, to assert ownership rights, the person working under contract (not am employee) to perform creative work must also relinquish their authorial rights by stipulating that their product is 'work for hire'. And unless they do, the creative result remains their property. (Typically, for example, architectural designs - but not the finished building - remain property of the architect, not the client, even if the client receives copies of those drawings.)
------------------------------
Kevin Coffee
Oneida Community Mansion House
Oneida, NY
Original Message:
Sent: 08-23-2016 10:18 AM
From: Olivia Lahs-Gonzales
Subject: Intellectual Property Contracts for Interns?
Years ago, I had a problem with an intern essentially taking the information that I had her research for a publication article that I was writing, and turning it into her own published essay that was quite similar to my take on the topic. I want to avoid this with other interns and wondered if anyone has their interns sign some sort of intellectual property contract that says that what they do for an institution stays with the institution. Your thoughts are appreciated!
------------------------------
Olivia Lahs-Gonzales
Director
The Sheldon Art Galleries
Saint Louis MO
------------------------------