The strength of magnetism is determined by the so-called "magnetic moment" - the dipole moment inside the atom, which comes from the angular momentum and electron spin. Materials have different structures of their own magnetic moments, depending on temperature. The Curie point is the temperature at which the intrinsic magnetic moments of the material change.
Permanent magnetism is due to the alignment of magnetic moments, and induced magnetism is created when disordered magnetic moments are forced to align in an applied magnetic field. For example, ordered magnetic moments (ferromagnetic) change and become disordered (paramagnetic) at the Curie temperature. Higher temperatures make the magnets weaker, since spontaneous magnetism occurs only below the Curie temperature - this is one of the main features of such spontaneous phenomena. Magnetic susceptibility above the Curie temperature can be calculated according to the Curie-Weiss law, which is obtained from the Curie law.
Usage and Formulas
By analogy with ferromagnetic and paramagnetic materials, the Curie temperature can also be used to describe the phase transition between ferroelectricity and paraelectricity. In this context, the order parameter is electric polarization, which goes from the final value to zero when the temperature rises above the Curie temperature.
Magnetic moments are constant dipole moments inside an atom that contain an electronic moment according to the relation μl = el / 2me, where me is the electron mass, μl is the magnetic moment, l is the angular momentum, without which it is difficult to calculate the Curie temperature; this ratio is called gyromagnetic.
Electrons in an atom introduce magnetic moments from their own angular momentum and from their orbital moment around the nucleus. The magnetic moments from the nucleus are negligible, unlike the magnetic moments from electrons. Thermal contributions lead to the appearance of higher electron energies, which violate the order and the destruction of the alignment between dipoles.
Features
Ferromagnetic, paramagnetic, ferrimagnetic and antiferromagnetic materials have different structures of the magnetic moment. At a certain Curie temperature of the material, these properties change. The transition from antiferromagnetic to paramagnetic (or vice versa) occurs at the Néel temperature, which is similar to the Curie temperature - this, in essence, is the main condition for such a transition.
Ferromagnetic, paramagnetic, ferrimagnetic and antiferromagnetic structures consist of intrinsic magnetic moments. If all the electrons inside the structure are paired, these moments are compensated due to their opposite spins and angular momenta. Thus, even when a magnetic field is applied, these materials have different properties and do not have a Curie temperature - for iron, for example, a completely different temperature is used.
The material is paramagnetic only above its Curie temperature. Paramagnetic materials are non-magnetic when there is no magnetic field and magnetic when a magnetic field is applied. When there is no magnetic field, the material has disordered magnetic moments; that is, the atoms are asymmetric and not aligned. When a magnetic field is present, the magnetic moments are temporarily rearranged parallel to the applied field, the atoms are symmetrical and aligned. Magnetic moments aligned in one direction cause an induced magnetic field.
For paramagnetism, this reaction to an applied magnetic field is positive and known as magnetic susceptibility. Magnetic susceptibility is applied only above the Curie temperature for disordered states.
Beyond the Curie Point
Above the Curie temperature, atoms are excited and the spin orientations become randomized, but can be rearranged by the applied field, i.e. the material becomes paramagnetic. Everything below the Curie temperature is space, the internal structure of which has already undergone a phase transition, the atoms are ordered, and the material itself has become ferromagnetic. The magnetic fields induced by paramagnetic materials are very weak compared to the magnetic fields of ferromagnetic materials.
Materials are only ferromagnetic below their respective Curie temperatures. Ferromagnetic materials are magnetic in the absence of an applied magnetic field.
When there is no magnetic field, the material has a spontaneous magnetization resulting from ordered magnetic moments. That is, for ferromagnetism, the atoms are symmetrical and aligned in one direction, creating a constant magnetic field.
Curie temperature for ferromagnets
Magnetic interactions are held together by exchange interactions; otherwise, thermal disorder would overcome the weak interaction of magnetic moments. Exchange interaction has zero probability of parallel electrons occupying the same point in time, which implies a preferred parallel alignment in the material. The Boltzmann factor makes a significant contribution, since he prefers that the interacting particles are aligned in one direction. This leads to the fact that ferromagnets have strong magnetic fields and high definitions of the Curie temperature of about 1000 K.
Ferrimagnetic materials are magnetic in the absence of an applied magnetic field and consist of two different ions.
Spontaneous magnetism
When there is no magnetic field, the material has spontaneous magnetism resulting from ordered magnetic moments; those. for ferrimagnetism, the magnetic moments of the same ionic moment are aligned in one direction with a certain magnitude, and the magnetic moments of another ion are directed in the opposite direction with a different magnitude. Since the magnetic moments have different values in opposite directions, there is spontaneous magnetism and a magnetic field is present.
What happens below the Curie point?
According to modern ferroelectric, the Curie temperature has its limitations. Like ferromagnetic materials, magnetic interactions are held together by exchange interactions. However, the moment orientations are antiparallel, which leads to a pure momentum, subtracting their momentum from each other.
Below the Curie temperature, the atoms of each ion are aligned in parallel with different momenta causing spontaneous magnetism; the material is ferrimagnetic. Above the Curie temperature, the material is paramagnetic, since the atoms lose their ordered magnetic moments when the material undergoes a phase transition.
Néel temperature and magnetism
The material has equal magnetic moments aligned in opposite directions, which leads to zero magnetic moment and zero magnetism at all temperatures below the Néel temperature. Antiferromagnetic materials are weakly magnetized in the absence of a magnetic field.
Like ferromagnetic materials, magnetic interactions are held together by exchange interactions, preventing thermal disorder from overcoming weak interactions of magnetic moments. When a disorder occurs, it is at Néel temperature.