[{"@context":"http:\/\/schema.org\/","@type":"BlogPosting","@id":"https:\/\/wiki.edu.vn\/en\/wiki24\/neel-effect-wikipedia\/#BlogPosting","mainEntityOfPage":"https:\/\/wiki.edu.vn\/en\/wiki24\/neel-effect-wikipedia\/","headline":"N\u00e9el effect – Wikipedia","name":"N\u00e9el effect – Wikipedia","description":"before-content-x4 From Wikipedia, the free encyclopedia after-content-x4 In superparamagnetism (a form of magnetism), the N\u00e9el effect appears when a superparamagnetic","datePublished":"2022-06-23","dateModified":"2022-06-23","author":{"@type":"Person","@id":"https:\/\/wiki.edu.vn\/en\/wiki24\/author\/lordneo\/#Person","name":"lordneo","url":"https:\/\/wiki.edu.vn\/en\/wiki24\/author\/lordneo\/","image":{"@type":"ImageObject","@id":"https:\/\/secure.gravatar.com\/avatar\/c9645c498c9701c88b89b8537773dd7c?s=96&d=mm&r=g","url":"https:\/\/secure.gravatar.com\/avatar\/c9645c498c9701c88b89b8537773dd7c?s=96&d=mm&r=g","height":96,"width":96}},"publisher":{"@type":"Organization","name":"Enzyklop\u00e4die","logo":{"@type":"ImageObject","@id":"https:\/\/wiki.edu.vn\/wiki4\/wp-content\/uploads\/2023\/08\/download.jpg","url":"https:\/\/wiki.edu.vn\/wiki4\/wp-content\/uploads\/2023\/08\/download.jpg","width":600,"height":60}},"image":{"@type":"ImageObject","@id":"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/a\/a0\/Effet_Neel_2.jpg\/220px-Effet_Neel_2.jpg","url":"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/a\/a0\/Effet_Neel_2.jpg\/220px-Effet_Neel_2.jpg","height":"148","width":"220"},"url":"https:\/\/wiki.edu.vn\/en\/wiki24\/neel-effect-wikipedia\/","about":["Wiki"],"wordCount":6123,"articleBody":"     (adsbygoogle = window.adsbygoogle || []).push({});before-content-x4From Wikipedia, the free encyclopedia       (adsbygoogle = window.adsbygoogle || []).push({});after-content-x4In superparamagnetism (a form of magnetism), the N\u00e9el effect appears when a superparamagnetic material in a conducting coil is subject to varying frequencies of magnetic fields. The non-linearity of the superparamagnetic material acts as a frequency mixer, with voltage measured at the coil terminals. It consists of several frequency components, at the initial frequency and at the frequencies of certain linear combinations. The frequency shift of the field to be measured allows for detection of a direct current field with a standard coil.         (adsbygoogle = window.adsbygoogle || []).push({});after-content-x4Magnetizing superparamagnetic materialTable of ContentsHistory[edit]Applications[edit]References[edit]See also[edit]History[edit]In 1949 French physicist Louis N\u00e9el (1904-2000) discovered that when they are finely divided, ferromagnetic nanoparticles lose their hysteresis below a certain size;[1][2] this phenomenon is known as superparamagnetism. The magnetization of these materials is subject to the applied field, which is highly non-linear.This curve is well described by the Langevin function, but for weak fields it can be simply written as:       (adsbygoogle = window.adsbygoogle || []).push({});after-content-x4M(H)=\u03c70H+NeH3+\u03b5(H3){displaystyle M(H)=chi _{0}H+N_{e}H^{3}+varepsilon (H^{3})},where \u03c70{displaystyle chi _{0}} is the susceptibility at zero field and Ne{displaystyle N_{e}} is known as the N\u00e9el coefficient. The N\u00e9el coefficient reflects the non-linearity of superparamagnetic materials in low fields.  Illustration of the N\u00e9el effectIf a coil of N{displaystyle N} turns with a surface S{displaystyle S} through which passes a current of excitation Iexc{displaystyle I_{text{exc}}} is immersed in a magnetic field Hext{displaystyle H_{ext}} collinear with the axis of the coil, a superparamagnetic material is deposited inside the coil.The electromotive force to the terminals of a winding of the coil, e{displaystyle e}, is given by the formula:e=\u2212d\u03d5\/dt=\u2212SdB\/dt{displaystyle e=-dphi \/dt=-SdB\/dt}where B{displaystyle B} is the magnetic induction given by the equation:B=\u03bc0\u03bcr(H+M){displaystyle B=mu _{0}mu _{r}(H+M)}In the absence of magnetic material,M=0{displaystyle M=0}andB=\u03bc0\u03bcr(Hext+Hexc){displaystyle B=mu _{0}mu _{r}(H_{ext}+H_{text{exc}})}.Differentiating this expression, the frequency of the voltage is the same as the excitation current iexc{displaystyle i_{text{exc}}} or the magnetic field Hext{displaystyle H_{ext}}.In the presence of superparamagnetic material, neglecting the higher terms of the Taylor expansion, we obtain for B:B=\u03bc0\u03bcr((1+\u03c70)(Hext+Hexc)+Ne(Hext+Hexc)3){displaystyle B=mu _{0}mu _{r}((1+chi _{0})(H_{ext}+H_{text{exc}})+N_{e}(H_{ext}+H_{text{exc}})^{3})}A new derivation of the first term of the equation \u03bc0\u03bcr(1+\u03c70)(Hext+Hexc){displaystyle mu _{0}mu _{r}(1+chi _{0})(H_{ext}+H_{text{exc}})} provides frequency voltage components of the stream of excitement iexc{displaystyle i_{text{exc}}} or the magnetic field Hext{displaystyle H_{ext}}.The development of the second term (Hext+Hexc)3=Hext3+3Hext2Hexc+3HextHexc2+Hexc3{displaystyle (H_{ext}+H_{text{exc}})^{3}=H_{ext}^{3}+3H_{ext}^{2}H_{text{exc}}+3H_{ext}H_{text{exc}}^{2}+H_{text{exc}}^{3}} multiplies the frequency components in which intermodular frequencies start components and generate their linear combinations. The non-linearity of the superparamagnetic material acts as a frequency mixer.Calling H(l){displaystyle H(l)} the total magnetic field within the coil at the abscissa, integrating the above induction coil along the abscissa between 0 and Lp{displaystyle L_{p}} and differentiating with respect to t{displaystyle t} obtains:u(t)=LdI(t)dt+FRogddt[\u222b0HLp(l)dl]+FNeel[\u222b0HLp(l)dl]I(t)dI(t)dt{displaystyle u(t)=L{frac {dI(t)}{dt}}+F_{Rog}{frac {d}{dt}}left[int _{0}^{H}Lp(l)dlright]+F_{text{Neel}}left[int _{0}^{H}Lp(l)dlright]I(t){frac {dI(t)}{dt}}}with Iexc(t)=Iexccos\u2061(wexct){displaystyle I_{text{exc}}(t)=I_{text{exc}}cos(w_{text{exc}}t)}  Spectral representation of the appearance of EMF due to the N\u00e9el effect around a high-frequency carrierThe conventional terms of self-inductance and Rogowski effect are found in both the original frequencies. The third term is due to the N\u00e9el effect; it reports the intermodulation between the excitation current and the external field.When the excitation current is sinusoidal, the effect is N\u00e9el characterized by the appearance of a second harmonic carrying the information flow field:u(t)=LIexcwexccos\u2061(wexct)+FRogddt[\u222b0LpHext(l)dl]+FNeel[\u222b0LpHext(l)dl]Iexc22wexcsin\u2061(2wexct){displaystyle u(t)=LI_{text{exc}}w_{text{exc}}cos(w_{text{exc}}t)+F_{Rog}{frac {d}{dt}}left[int _{0}^{Lp}H_{ext}(l)dlright]+F_{text{Neel}}left[int _{0}^{Lp}H_{ext}(l)dlright]{frac {I_{text{exc}}^{2}}{2}}w_{text{exc}}sin(2w_{text{exc}}t)}Applications[edit]  Design of N\u00e9el-effect current sensorAn important application of the N\u00e9el effect is as a current sensor, measuring the magnetic field radiated by a conductor with a current;[3] this is the principle of N\u00e9el effect current sensors.[4] The N\u00e9el effect allows the accurate measurement of currents with very low-frequency-type sensors in a current transformer without contact.The transducer of a N\u00e9el-effect current sensor consists of a coil with a core of superparamagnetic nanoparticles. The coil is traversed by a current excitation:iexc(t){displaystyle i_{text{exc}}(t)}.In the presence of an external magnetic field to be measured:Hext(t){displaystyle H_{ext}(t)}the transducer transposes (with the N\u00e9el effect) the information to be measured, H (f) around a carrier frequency, the harmonic of order 2 excitation current 2:fexc{displaystyle f_{text{exc}}}which is simpler. The electromotive force generated by the coil is proportional to the magnetic field to measure:Hext(t){displaystyle H_{ext}(t)}and to the square of the excitation current:fem(t)=FNeeliexc2(t)H(t){displaystyle fem(t)=F_{text{Neel}}i_{text{exc}}^{2}(t)H(t)}To improve the measurement’s performance (such as linearity and sensitivity to temperature and vibration), the sensor includes a second permanent winding-reaction against it to cancel the second harmonic. The relationship of the current reaction against the primary current is proportional to the number of turns against reaction:Icr=Ip\/Ncr{displaystyle I_{cr}=I_{p}\/N_{cr}}.References[edit]See also[edit]       (adsbygoogle = window.adsbygoogle || []).push({});after-content-x4"},{"@context":"http:\/\/schema.org\/","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"https:\/\/wiki.edu.vn\/en\/wiki24\/#breadcrumbitem","name":"Enzyklop\u00e4die"}},{"@type":"ListItem","position":2,"item":{"@id":"https:\/\/wiki.edu.vn\/en\/wiki24\/neel-effect-wikipedia\/#breadcrumbitem","name":"N\u00e9el effect – Wikipedia"}}]}]