How can I skip xml declaration when serializing?

I'm trying to output a xml file without xml head like I tried:

Type t = obj.GetType();
XmlSerializer xs=new XmlSerializer(t);
XmlWriter xw = XmlWriter.Create(@"company.xml",
                                        new XmlWriterSettings() { OmitXmlDeclaration = true, Indent = true });
xs.Serialize(xw,obj);
xw.Close();

But it's still outputing in the xml file. I don't want string tricks. Any ideas?