China’s exports of rare earth permanent magnets to Japan slightly rebounded in April after slumping the previous month, but Japanese firms warn they are facing “severe” shortages as a diplomatic row between Beijing and Tokyo grinds on.Shipments of permanent magnets from China to Japan rose by 2.5 per cent in April compared with the previous month, according to Chinese customs data released on Wednesday. But the modest rise only partly offset the 17.3 per cent plunge recorded in March.The...