Atomic magnetism – origin of orbital magnetic dipole moment The orbital magnetic dipole moment of an electron arises due to which physical effect?

Introduction / Context:
Magnetic moments in atoms have two principal contributions: orbital and spin. Distinguishing these is essential for understanding paramagnetism, diamagnetism, and fine structure in atomic spectra, as well as the magnetic behavior of solids.

Given Data / Assumptions:

• Electron is bound in an atom and can possess orbital angular momentum L and spin angular momentum S.
• Magnetic moments couple to external magnetic fields, giving rise to Zeeman splitting.
• Quantum description replaces classical orbits with stationary states but retains the concept of orbital angular momentum.

Concept / Approach:

Classically, a charged particle moving in a loop constitutes a current and therefore a magnetic dipole. In quantum mechanics, an electron with orbital angular momentum has an associated orbital magnetic moment proportional to L. Independently, the electron spin gives a spin magnetic moment proportional to S. Total atomic magnetic behavior results from vector addition of these contributions (with Landé g-factors) and their interactions with crystal fields and spin–orbit coupling.

Step-by-Step Solution:

Verification / Alternative check:

Spectroscopic measurements and atomic structure calculations show distinct contributions, confirming that orbital motion indeed generates a magnetic dipole moment in addition to spin.

Why Other Options Are Wrong:

(b) denies the well-established orbital contribution. (c) phonons modulate magnetic interactions but do not create an electronic magnetic dipole. (d) nuclear spin moments exist but are much smaller and are not the origin of the electron’s orbital moment.

Common Pitfalls:

Assuming Bohr orbits literally; while modern theory is quantum, the association between L and mu_L remains valid.

Final Answer:

True – the motion of the electron in its atomic orbit around the nucleus