1- To obtain full core files on AIX, set the following ulimit options:
ulimit -c unlimited turn on corefiles with unlimited size
ulimit -n unlimited allows an unlimited number of open file
descriptors
ulimit -d unlimited sets the user data limit to unlimited
ulimit -f unlimited sets the file limit to unlimited

You can display the current ulimit settings with:
ulimit -a

2- Set the following in smitty:
1. Start smitty as root
2. Go to System Environments -> Change/Show Characteristics of Operating System
3. Set the Enable full CORE dump option to TRUE

Alternatively, you can run chdev -l sys0 -a fullcore=’true’ as root.

You can check the setting with lsattr -D -c sys -a fullcore -H, which should produce output similar to this:
attribute deflt description user_settable
fullcore false Enable full CORE dump True

Reference: IBM Web Site, AIX Help