Summary Companies Korean firm plans factory that alone could meet half U.S. demand Chinese Apple supplier to open magnet plant this year -sources Vietnam's rare earths deposits second only to China's China dominates world's magnet supply HANOI/SEOUL, Aug 22 (Reuters) - Korean and Chinese magnet firms, including an Apple supplier, are set to open factories in Vietnam, according to documents and people familiar with the plans, amid a push to diversify supply chains away from China and defend against Sino-U.S. tension. South Korea's Star Group Industrial (SGI) and China's Baotou INST Magnetic would join companies in sectors as varied as...