The temperature at which a ferromagnet (or ferroelectric) loses its spontaneous magnetization (or polarization); above it the material is paramagnetic. About 770 °C for iron and about 358 °C for nickel.
Japanese name: キュリー温度
Curie temperature appears in 4 practice questions across 3 topics, including Magnetic materials, Electronic, magnetic and optical materials, Thermal properties of materials.
In a ferromagnet, the exchange interaction aligns the magnetic moments of atoms, producing spontaneous magnetization. As temperature rises, thermal motion disturbs this order, the spontaneous magnetization gradually shrinks, and it reaches zero at the Curie temperature. Above it the material is paramagnetic. Curie temperatures are about 770 °C (1043 K) for iron, about 358 °C for nickel, about 1120 °C for cobalt and about 20 °C for gadolinium; Nd₂Fe₁₄B, the main phase of neodymium magnets, is about 310 °C, and magnetite (Fe₃O₄) about 580 °C.
Above the Curie temperature, the magnetic susceptibility follows the Curie–Weiss law χ = C/(T − θ), rising sharply as the temperature falls toward θ. θ is called the paramagnetic Curie temperature and is close to the Curie temperature. Ferroelectrics behave similarly, with the permittivity becoming very large near the Curie temperature; BaTiO₃ shows a sharp maximum in permittivity at about 120 °C. The Curie temperature is found by measuring the temperature dependence of magnetization with a magnetic balance, or from small anomalies in DSC or thermal expansion.
Iron loses its ferromagnetism at 770 °C, but its crystal structure remains BCC α-iron; it changes to FCC only at 912 °C. Iron in this range was once called β-iron, but since no structural change is involved, it is no longer regarded as a separate phase. The temperature at which antiferromagnetic order disappears is called the Néel temperature and is distinguished from the Curie temperature. Permanent magnets suffer irreversible demagnetization from falling coercivity at temperatures far below the Curie temperature, so their maximum service temperatures are set well below it.
The abrupt change in magnetism at the Curie temperature is used for temperature control. Rice cookers, for example, once used a mechanism with a temperature-sensitive ferrite that stops being attracted to a magnet at a certain temperature, cutting the heating when the rice is done and the temperature rises. Some soldering irons keep their temperature constant automatically by using a magnetic material in the tip that heats less readily above its Curie temperature. The way magnetite in rocks records the direction of Earth's magnetic field as it cools below its Curie temperature is the basis of paleomagnetic research.
Answer: C. It becomes paramagnetic
In a ferromagnet, the magnetic moments of neighboring atoms are aligned in the same direction by the exchange interaction, giving a spontaneous magnetization. As temperature rises, thermal motion disturbs the alignment, and above the Curie temperature the spontaneous magnetization disappears, leaving paramagnetism, a slight magnetization only when an external field is applied. The Curie temperature is about 770 °C for iron, about 358 °C for nickel and about 1120 °C for cobalt. Antiferromagnetism is an ordered state in which neighboring moments align antiparallel, and the temperature at which that order disappears is called the Néel temperature. Diamagnetism is a weak property of all substances and does not appear as a result of ferromagnetism vanishing.
The Curie temperature is where ferromagnets and ferrimagnets lose their spontaneous magnetization, and the Néel temperature is where antiferromagnets lose their antiparallel order. Above either temperature the material becomes paramagnetic.
No. 770 °C is the temperature of the magnetic transformation, at which only magnetic order is lost while the structure stays BCC, and it is called the A2 point on the Fe–C phase diagram. The crystal structure changes to FCC at 912 °C (the A3 point).
It becomes ferromagnetic again on cooling, but its magnetic domains point in random directions, so its strength as a magnet remains lost. To use it, it must be magnetized again in a strong field. If its microstructure has changed, its performance will not recover either.
As temperature rises, thermal motion disturbs the alignment, and above the Curie temperature the spontaneous magnetization disappears, leaving paramagnetism, a slight magnetization only when an external field is applied.
When ferromagnetic iron is heated above its Curie temperatu…Moments randomized by thermal vibration describe the paramagnetic state above the Curie temperature.
What is the main reason a ferromagnet splits into many magn…Nd₂Fe₁₄B has a rather low Curie temperature of about 310°C, and as the temperature rises its magnetocrystalline anisotropy falls and its coercivity drops sharply.
What is the main purpose of adding Dy or Tb to neodymium ma…As a result, the linear expansion coefficient is as small as about 1×10⁻⁶ K⁻¹ below the Curie temperature, and Invar is used in precision measuring instruments, containers for liquefied natural gas and the like.
Which statement correctly explains why the linear thermal e…Magnetic domain Domain wall Magnetocrystalline anisotropy Coercivity Saturation magnetization Maximum energy product Coefficient of linear thermal expansion Invar Indirect-bandgap semiconductor Matthiessen's rule