Magnetic phase transitions occur when materials change their magnetic ordering due to temperature or external fields. In ferromagnetic materials below the Curie temperature, electron spins align parallel, creating ordered magnetic domains. As temperature increases toward the transition point, thermal energy disrupts this alignment, causing dramatic changes in electrical resistance and other transport properties.
The magnetoresistance effect demonstrates how electrical resistance changes across magnetic transitions. At low temperatures in the ferromagnetic phase, electron spins are aligned and conduction is efficient. Near the Curie temperature, magnetic fluctuations increase electron scattering, causing resistance to rise sharply. Above the transition, in the paramagnetic phase, random spin orientations lead to maximum scattering and highest resistance.
Colossal Magnetoresistance represents an extreme case where electrical resistance can change by orders of magnitude in response to magnetic fields. In materials like manganites, the coupling between magnetic ordering and charge transport is so strong that applying a magnetic field dramatically reduces resistance. This occurs because the magnetic field aligns electron spins, creating more efficient conduction pathways and reducing scattering.
The Hall effect provides crucial insights into how magnetic transitions affect charge transport. When current flows through a material in a magnetic field, charge carriers are deflected, creating a Hall voltage. The Hall coefficient reveals both carrier density and type. Across magnetic transitions, dramatic changes in the Hall coefficient indicate fundamental alterations in the electronic structure and carrier dynamics.
The understanding of electricity-magnetic transitions has revolutionized modern technology. Magnetic Random Access Memory uses magnetic states to store data with high speed and low power consumption. Spintronics exploits electron spin for novel computing architectures. Magnetic sensors enable precise field detection. From the discovery of giant magnetoresistance in the 1980s to today's quantum computing research, these phenomena continue driving technological innovation toward more efficient and powerful electronic devices.