Formal:
* Diary
* Logbook
* Ledger
* Record
* Chronicle
* Annals
* Memoirs
Informal:
* Notebook
* Scribble pad
* Daybook
* Notepad
* Log
Other options:
* Publication (if referring to a published journal)
* Periodical (if referring to a regularly published journal)
* Magazine (if referring to a magazine-style journal)
* Newspaper (if referring to a daily news journal)
It's helpful to provide more context about what you're writing about so I can give you a more precise synonym!