The University of Michigan last year invested $30 million in a private equity firm that buys and renovates homes out of tax foreclosure. One U-M professor fears the arrangement could make the university an “unintentional de facto slumlord.” The eviction notice arrived last month at William Nunley’s modest two-story house in Detroit’s Fitzgerald neighborhood, one of the hottest real-estate markets in the city. He had lived in the house for three years with his wife and their three children and had hoped to buy it from their landlord.