TOKYO, July 7 : The trust bank unit of Japan's Sumitomo Mitsui Trust Group will acquire a 15 per cent stake in infrastructure investment manager Morrison and make an initial $500 million commitment to two Morrison strategies, the companies said on Tuesday. The 15 per cent stake is expected to be in the tens of billions of yen, Sumitomo Mitsui said.The return of inflation is encouraging Japanese investors to seek higher returns on their assets. Alternative assets - a broad class that includes infrastructure - are a small but fast-growing area for asset managers seeking to deploy Japanese capital. Morrison will become Sumitomo Mitsui Trust Bank's (SMTB) preferred global infrastructure manager. The companies have also agreed to collaborate on raising third-party capital for each other's infra