Superparamagnetism is a phenomenon observed in small magnetic particles, typically less than 20 nanometers in diameter. In these particles, thermal energy can overcome the magnetic interactions that normally keep them aligned. As a result, they can randomly flip their magnetic orientation, leading to no net magnetization in the absence of an external magnetic field. When an external magnetic field is applied, superparamagnetic particles can become magnetized, aligning their magnetic moments. This property makes them useful in various applications, such as in magnetic nanoparticles for medical imaging and data storage, where they can be easily manipulated without residual magnetism when the field is removed.