Peningkatan Sifat Magnetik Magnet Permanen Nanokomposit (Ba1-xLax)Fe12O19/Co0,6Zn0,4Fe2O4 melalui Sintesa Pemaduan Mekanik dan Destruksi Ultrasonik = Magnetic Properties Enhancement in Nanocomposite (Ba1-xLax)Fe12O19/Co0,6Zn0,4Fe2O4 Permanent Magnets by Mechanical Alloying and Ultrasonic Irradiation.