ParamagnetismusEigenschaft

Paramagnetism is a form of magnetism in which materials are weakly attracted to external magnetic fields due to the presence of unpaired electron spins. In the absence of a field, paramagnetic materials do not retain magnetization; their net magnetization vanishes when the field is removed, aside from trace impurities.

Origin and behavior: Paramagnetism arises when atoms or ions contain unpaired electrons whose magnetic moments align with an applied field. Thermal agitation randomizes spins, so the resulting magnetization is typically small and proportional to the applied field. The magnetic susceptibility χ is positive but small. Many paramagnets follow Curie’s law, χ = C/T, at higher temperatures, where C is the Curie constant. If interactions between moments exist, Curie-Weiss law χ = C/(T − θ) applies, with θ indicating effective magnetic interactions (positive for ferromagnetic-like and negative for antiferromagnetic-like correlations). At room temperature, the response is usually linear and non-hysteretic.

Types and sources: Localized-moment paramagnetism occurs in ions and molecules with discrete unpaired electrons. Pauli paramagnetism arises from the spin of conduction electrons in metals and is typically very small and weakly temperature dependent.

Examples and applications: Oxygen is a classic strongly paramagnetic gas due to two unpaired electrons. Many transition-metal salts and rare-earth compounds exhibit paramagnetism with varying strengths. In metals, elements such as platinum and aluminum show weak Pauli paramagnetism. Paramagnetic materials are used in applications such as magnetic resonance imaging (MRI) contrast agents, where high-spin lanthanide complexes (for example gadolinium compounds) enhance relaxation processes.

Relation to other magnetism: Diamagnetism involves induced currents that oppose external fields and yields negative χ. Ferromagnetism features spontaneous magnetization and hysteresis below a critical temperature. Paramagnetism differs by its absence of spontaneous order and by its reversible, field-induced response.