A flat circular loop of radius \(R\) carries a steady current \(I\). The loop is initially oriented in a uniform magnetic field \(\vec{B}\) such that its magnetic dipole moment \(\vec{\mu}\) is aligned parallel to \(\vec{B}\). An external agent slowly rotates the loop until its magnetic dipole moment makes an angle \(\theta\) with \(\vec{B}\). Which of the following expressions represents the work done by the external agent on the loop during this rotation?