As the assets in an IRA account are not eligible to be pledged as loan collateral, and stock ordinarily serves as the collateral securing payment of a margin loan, account holders are not permitted to buy stock on margin in either a Cash or Margin type IRA account. All stock purchases must be paid for in full with cash. In addition, other transactions which require a margin account such as shorting stock and selling uncovered options are not allowed in either a Cash or Margin type IRA account.
For additional information regarding trading permissions in Cash and Margin type IRA accounts see the Interactive Brokers Knowledge Base.