Editing Magnetocaloric effect (section)

=== Paramagnetic salts ===

The original proposed refrigerant was a [[paramagnetism|paramagnetic]] [[salt (chemistry)|salt]], such as [[cerium]] [[magnesium]] [[nitrate]].  The active magnetic dipoles in this case are those of the [[electron shell]]s of the paramagnetic atoms.

In a paramagnetic salt ADR, the heat sink is usually provided by a pumped {{chem|4|He}} (about 1.2&nbsp;K) or {{chem|3|He}} (about 0.3&nbsp;K) [[cryostat]].  An easily attainable 1&nbsp;T magnetic field is generally required for initial magnetization. The minimum temperature attainable is determined by the self-magnetization tendencies of the refrigerant salt, but temperatures from 1 to 100 mK are accessible. [[Dilution refrigerator]]s had for many years supplanted paramagnetic salt ADRs, but interest in space-based and simple to use lab-ADRs has remained, due to the complexity and unreliability of the dilution refrigerator.

At a low enough temperature, paramagnetic salts become either [[diamagnetism|diamagnetic]] or ferromagnetic, limiting the lowest temperature that can be reached using this method.{{Citation needed|reason=What is this transition temperature called?|date=June 2023}}