\(\text { centre }=4 \times \frac{\mu_{0} i}{4 \pi \times \frac{L}{2}} \times\left(2 \sin 45^{\circ}\right)=\frac{2 \sqrt{2} \mu_{0} i}{\pi L }\)
\(M =\frac{\text { Flux through inner loop }}{ i }\)
\(M =\frac{2 \sqrt{2} \mu_{0} \ell^{2}}{\pi L }\)