Instantiate a prefab material

Hi, I can't find how to add a prefab on the scene by script, without having a material instance. I do it this way:

             m_lastSpawnedObject = Instantiate(m_ObjectSpawned, transform);//set as a child
             m_lastSpawnedObject.transform.localPosition = SpawnPosition;

At this point I checked the newly created object material, and it is already an instance.

Then I set the material this way, but material is still an instance:

       m_lastSpawnedObject.GetComponent<Renderer>().sharedMaterial = material; 

Please help! What I'm doing wrong?