Hi,
SM19 tcode is used to activate security audit. Through that you can have a log of User Login ,Logoff Failed attempt,Transaction start,Report start & system related log.That log you can view through t code.
There is no such T-code that record log related to MM module. You have to check individually i.e. For material master changes log ,you can view through MM02/MM03.For PO me23n/Me22n etc.
I mean to say ,you have to run individual tocde for viewing log.
Thanx