Sprite cutting when changing material

Hi, i have a problem with unity sprite renderer. When I put sprite on scene with default sprite material, edges are smooth. However when I change material, sprite get cut and / or losing all round edges. How can i change this?

Standard sprite:


With changed material:


Thanks in advance for all answers.

 

Well, first smooth picture is standard sprites-default material (simply drag and dropped sprite on scene). Second one is standard diffuse unity material. I drag and dropped sprite on scene and then created simple diffuse material, and changed material of the sprite. I did this so I could use shared material to change all objects color with script attached to one object.