A loop carrying current $I$ lies in the $x y$-plane in the figure. The unit vector $\hat{\mathbf{k}}$ is coming out of the plane of the paper. The magnetic moment of the current loop is
(a) $a^{2} l \hat{k}$
(b) $\left(\frac{\pi}{2}+1\right) a^{2} l \hat{\hat{k}}$
(c) $-\left(\frac{\pi}{2}+1\right) a^{2} / \hat{k}$
(d) $(2 \pi+1) a^{2} / \hat{k}$