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Our next class will be on how slavery developed in the USA and how it shaped its society. But I've noticed that the available texts and materials are somewhat limited
Limited?!? Hardly!
Here are some general bibliographies on slavery. Not every item here is specific to the United States but you'll find loads of relevant stuff.
I'm not an expert on US slavery by any means but I'll close with a personal recommendation for one book in particular: The Plantation by E. T. Thompson. It's old but it's a classic, short and readable. It focuses on the US (specifically coastal Virginia) but it emphasizes general patterns that are relevant to Brazil and other contexts.