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维基百科

居里点

居里点({英語:Curie point),又作居里温度(Curie temperature,Tc)或磁性转变点。是指磁性材料中自发磁化强度降到零时的温度,是铁磁性亚铁磁性物质转变成顺磁性物质的临界点。低于居里点温度时该物质成为铁磁体,此时和材料有关的磁场很难改变。当温度高于居里点时,该物质成为顺磁体,磁体的磁场很容易随周围磁场的改变而改变。这时的磁敏感度约为10-6。居里点由物质的化学成分和晶体结构决定。居里温度是以皮埃尔·居里命名的,他表明在临界温度下磁性材料会失去磁性。

居里點的溫度可以用平均場理論估計。

材料的居里温度[1][2][3]
材料 居里
温度 (K)
(Fe) 1043
(Co) 1400
(Ni) 627
(Gd) 292
(Dy) 88
铋化锰 (MnBi) 630
锑化锰(MnSb) 587
二氧化铬 (CrO2) 386
化锰 318
氧化铕 69
氧化铁 (Fe2O3) 948
四氧化三铁 (FeOFe2O3) 858
氧化镍-氧化铁NiO–Fe2O3 858
氧化铜-氧化铁CuO–Fe2O3 728
氧化镁-氧化铁MgO–Fe2O3 713
氧化锰-氧化铁MnO–Fe2O3 573
钇铁石榴石 (Y3Fe5O12) 560
钕磁铁 583-673
铝镍钴合金 973-1133
钐钴磁铁 993-1073
锶铁氧体 723

磁矩

磁矩是原子内的永久偶极矩,包含电子的角动量和自旋[4],他们之间的关系是 μl = el/2me, me 是电子质量, μl 是磁矩, l是角动量; 这个比例被称作 gyromagnetic ratio旋磁比).

原子中的电子从它们自己的角动量和它们围绕原子核的轨道动量贡献磁矩。与来自电子的磁矩相比,来自原子核的磁矩是微不足道的。[5] 热作用在更高能量的电子上结果就是扰乱了秩序,并破坏了偶极子之间的对齐。

铁磁性, 顺磁性, 亚铁磁性反铁磁性材料有不同的固有磁矩结构。在材料特定的居里温度下,这些属性会发生变化。从反铁磁性到顺磁性(或反之亦然)的过渡发生在奈尔温度, 这与居里温度类似。

低于TC 高于TC
铁磁性 顺磁性
亚铁磁性 顺磁性
反铁磁性 顺磁性

在居里温度下改变特性的具有磁矩的材料

铁磁性,顺磁性,亚铁磁性和反铁磁性结构由固有磁矩组成。 如果结构中的所有电子都配对,则由于它们的相反自旋和角动量,这些力矩会抵消。 因此,即使施加磁场,这些材料也具有不同的性质,并且没有居里温度。[6][7]

顺磁性

当一些材料的温度高于居里点时,材料会表现出顺磁性,这样的材料叫顺磁性材料。当没有受到外部磁场的影响时,顺磁性材料不会表现磁性;反之则会表现磁性。没有受到外部磁场影响时,材料内部的磁矩是无序排列的。也就是说,材料内部的粒子不整齐且没有顺磁力线方向排列。当受到磁场影响时,这些磁矩会顺磁场线整齐排列[8][9][10],并且产生感应磁场[10][11]。 对于顺磁性,这种对外加磁场的响应是正的,称为磁化率[6] 磁化率仅适用于居里温度以上的无序状态。[12]

顺磁性的来源(具有居里温度的材料)包括:[13]

  • 全部含有未配对电子的原子;
  • 内电子层未被完全填充的原子;
  • 自由基
  • 金属。

超過居禮溫度後,原子被激發, 旋轉的方向變成隨機的[7] 不過可以被作用場重新調整, 即材料变为顺磁性。在居里温度以下,材料的固有结构经历了一次相变相变[14] 原子变为有序,材料具有铁磁性。[10] 与铁磁性材料的磁场相比,顺磁性材料的感应磁场非常弱。[14]

铁磁性

材料仅在其相应的居里温度以下具有铁磁性。在没有外加磁场的情况下,铁磁材料具有磁性。

当没有外加磁场时,材料具有自发磁化英语Spontaneous magnetization,这是有序磁矩的结果;也就是说,对于铁磁性材料,原子具有某种对称性并且在同一方向上排列,从而产生永久磁场。

磁性相互作用通过交换相互作用结合在一起;否则,热无序将克服磁矩的弱相互作用。交换相互作用的平行电子占据同一时间点的可能性为零,这意味着材料中会有一个倾向的平行排列。[15] 在这个过程中,玻尔兹曼因子贡献很大,因为它倾向于使相互作用的粒子在同一方向上排列。[16] 这会导致铁磁体具有较强的磁场和较高的居里温度,约 1000K(730℃)[17]

在居里温度以下,原子有序排列,从而导致自发磁性,材料具有铁磁性。在居里温度以上,该材料是顺磁性的,因为当该材料经历相变时,原子会失去其有序的磁矩。[14]

亚铁磁性

材料仅在其相应的居里温度以下具有亚铁磁性。在没有外加磁场的情况下,亚铁磁材料具有磁性,并由两种不同离子组成。[18]

当没有外加磁场时,材料具有自发磁化,这是有序磁矩的结果;也就是说,对于亚铁磁性材料,一种离子的磁矩对准一个方向,有一个大小,另一种离子的磁矩对准相反方向,有一个不同的大小。因为磁矩在相反的方向有着不同的大小,所以仍然有自发磁化,存在磁场。[18]

和铁磁性材料相似,磁性相互作用通过交换相互作用结合在一起。但是,磁矩的方向是反平行的,导致净势是一个减另一个。[18]

低于居里点时,每个离子的原子都反平行对齐,有着不同的磁矩,造成自发磁化;材料具有亚铁磁性。高于居里点时,该材料是顺磁性的,因为当该材料经历相变时,原子会失去其有序的磁矩。[18]

反铁磁性与奈尔温度

材料仅在其相应的奈尔温度以下具有反铁磁性。这与居里温度相似,高于奈尔温度时,该材料经历相变,变成顺磁性。也就是说,热能变得足够大,足以破坏材料内的微观磁有序性。 [19]它以路易·奈尔(Louis Néel,1904-2000 年)的名字命名,他因在该领域的工作而获得了 1970 年的诺贝尔物理学奖

材料有方向相反的相等磁矩,导致在奈尔温度以下磁矩为零和净磁性为零。反铁磁性材料在有或没有外加磁场的情况下有很弱的磁性。

与铁磁性材料相似,磁性相互作用通过交换相互作用结合在一起;否则,热无序将克服磁矩的弱相互作用。[15][20]奈尔温度时无序出现。[20]

下面列表中有几种物质的奈尔温度:[21]

Substance Néel temperature (K)
MnO 116
MnS 160
MnTe 307
MnF2 67
FeF2 79
FeCl2 24
FeI2 9
FeO 198
FeOCl英语Iron oxychloride 80
CrCl2 25
CrI2 12
CoO 291
NiCl2 50
NiI2 75
NiO 525
KFeO2 983[22]
Cr 308
Cr2O3 307
Nd5Ge3 50

参见

参考资料

引用

  1. ^ Buschow 2001,p5021, table 1
  2. ^ Jullien & Guinier 1989,第155頁
  3. ^ Kittel 1986
  4. ^ Hall & Hook 1994,第200頁
  5. ^ Jullien & Guinier 1989,第136–38頁
  6. ^ 6.0 6.1 Ibach & Lüth 2009
  7. ^ 7.0 7.1 Levy 1968,第236–39頁
  8. ^ Dekker 1958,第217–20頁
  9. ^ Levy 1968
  10. ^ 10.0 10.1 10.2 Fan 1987,第164–65頁
  11. ^ Dekker 1958,第454–55頁
  12. ^ Mendelssohn 1977,第162頁
  13. ^ Levy 1968,第198–202頁
  14. ^ 14.0 14.1 14.2 Cusack 1958,第269頁
  15. ^ 15.0 15.1 15.2 15.3 Hall & Hook 1994,第220–21頁
  16. ^ Palmer 2007
  17. ^ Hall & Hook 1994,第220頁
  18. ^ 18.0 18.1 18.2 18.3 Jullien & Guinier 1989,第158–59頁
  19. ^ Spaldin, Nicola A. Magnetic materials : fundamentals and device applications Repr. Cambridge: Cambridge Univ. Press. 2006: 89–106. ISBN 9780521016582. 
  20. ^ 20.0 20.1 Jullien & Guinier 1989,第156–57頁
  21. ^ Kittel, Charles. Introduction to Solid State Physics 8th. New York: John Wiley & Sons. 2005. ISBN 978-0-471-41526-8. 
  22. ^ Ichida, Toshio. Mössbauer Study of the Thermal Decomposition Products of K2FeO4. Bulletin of the Chemical Society of Japan. 1973, 46 (1): 79–82. doi:10.1246/bcsj.46.79 . 
  23. ^ Jullien & Guinier 1989,第153頁
  24. ^ Hall & Hook 1994,第205–06頁
  25. ^ 25.0 25.1 Levy 1968,第201–02頁
  26. ^ Kittel 1996,第444頁
  27. ^ Myers 1997,第334–45頁
  28. ^ 28.0 28.1 Hall & Hook 1994,第227–28頁
  29. ^ Kittel 1986,第424–26頁
  30. ^ Spaldin 2010,第52–54頁
  31. ^ Hall & Hook 1994,第225頁
  32. ^ Mendelssohn 1977,第180–81頁
  33. ^ Mendelssohn 1977,第167頁
  34. ^ 34.0 34.1 34.2 34.3 34.4 34.5 Bertoldi, Bringa & Miranda 2012
  35. ^ Brout 1965,第6–7頁
  36. ^ 36.0 36.1 Jullien & Guinier 1989,第161頁
  37. ^ 37.0 37.1 Rau, Jin & Robert 1988
  38. ^ 38.0 38.1 Skomski & Sellmyer 2000
  39. ^ 39.0 39.1 Jullien & Guinier 1989,第138頁
  40. ^ Hall & Hook 1994
  41. ^ 41.0 41.1 Hwang et al. 1998
  42. ^ 42.0 42.1 Paulsen et al. 2003
  43. ^ 43.0 43.1 López Domínguez et al. 2013
  44. ^ 44.0 44.1 44.2 44.3 Bose et al. 2011
  45. ^ 45.0 45.1 Sadoc et al. 2010
  46. ^ 46.0 46.1 Webster 1999
  47. ^ Kovetz 1990,第116頁
  48. ^ Myers 1997,第404–05頁
  49. ^ Pascoe 1973,第190–91頁
  50. ^ Webster 1999,第6.55–6.56頁
  51. ^ Takamatsu. Demonstration of Control Rod Holding Stability of the Self Actuated Shutdown System in Joyo for Enhancement of Fast Reactor Inherent Safety. Journal of Nuclear Science and Technology. 
  52. ^ TMT-9000S
  53. ^ Pallàs-Areny & Webster 2001,第262–63頁

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居里点, 此條目目前正依照en, curie, temperature上的内容进行翻译, 2019年4月7日, 如果您擅长翻译, 並清楚本條目的領域, 欢迎协助翻譯, 改善或校对本條目, 此外, 长期闲置, 未翻譯或影響閱讀的内容可能会被移除, 英語, curie, point, 又作居里温度, curie, temperature, 或磁性转变点, 是指磁性材料中自发磁化强度降到零时的温度, 是铁磁性或亚铁磁性物质转变成顺磁性物质的临界点, 低于温度时该物质成为铁磁体, 此时和材料有关的磁场很难改变, 当温度高于. 此條目目前正依照en Curie temperature上的内容进行翻译 2019年4月7日 如果您擅长翻译 並清楚本條目的領域 欢迎协助翻譯 改善或校对本條目 此外 长期闲置 未翻譯或影響閱讀的内容可能会被移除 居里点 英語 Curie point 又作居里温度 Curie temperature Tc 或磁性转变点 是指磁性材料中自发磁化强度降到零时的温度 是铁磁性或亚铁磁性物质转变成顺磁性物质的临界点 低于居里点温度时该物质成为铁磁体 此时和材料有关的磁场很难改变 当温度高于居里点时 该物质成为顺磁体 磁体的磁场很容易随周围磁场的改变而改变 这时的磁敏感度约为10 6 居里点由物质的化学成分和晶体结构决定 居里温度是以皮埃尔 居里命名的 他表明在临界温度下磁性材料会失去磁性 居里點的溫度可以用平均場理論估計 材料的居里温度 1 2 3 材料 居里 温度 K 铁 Fe 1043钴 Co 1400镍 Ni 627钆 Gd 292镝 Dy 88铋化锰 MnBi 630锑化锰 MnSb 587二氧化铬 CrO2 386砷化锰 318氧化铕 69氧化铁 Fe2O3 948四氧化三铁 FeOFe2O3 858氧化镍 氧化铁NiO Fe2O3 858氧化铜 氧化铁CuO Fe2O3 728氧化镁 氧化铁MgO Fe2O3 713氧化锰 氧化铁MnO Fe2O3 573钇铁石榴石 Y3Fe5O12 560钕磁铁 583 673铝镍钴合金 973 1133钐钴磁铁 993 1073锶铁氧体 723目录 1 磁矩 2 在居里温度下改变特性的具有磁矩的材料 2 1 顺磁性 2 2 铁磁性 2 3 亚铁磁性 2 4 反铁磁性与奈尔温度 3 居里 韦斯定律 4 物理 4 1 从上方接近居里温度 4 2 从下方接近居里温度 4 3 接近绝对零度 0开尔文 4 4 Ising相变模型 4 5 Weiss磁畴和表面和体积居里温度 4 6 更改材料的居里温度 4 6 1 Composite materials 4 6 2 Particle size 4 6 3 Pressure 4 6 4 Orbital ordering 5 铁电材料中的居里温度 5 1 Ferroelectric and dielectric 5 2 相对介电常数 6 应用 7 参见 8 参考资料 8 1 引用 8 2 来源磁矩 编辑磁矩是原子内的永久偶极矩 包含电子的角动量和自旋 4 他们之间的关系是 ml el 2me me 是电子质量 ml 是磁矩 l是角动量 这个比例被称作 gyromagnetic ratio 旋磁比 原子中的电子从它们自己的角动量和它们围绕原子核的轨道动量贡献磁矩 与来自电子的磁矩相比 来自原子核的磁矩是微不足道的 5 热作用在更高能量的电子上结果就是扰乱了秩序 并破坏了偶极子之间的对齐 铁磁性 顺磁性 亚铁磁性和反铁磁性材料有不同的固有磁矩结构 在材料特定的居里温度下 这些属性会发生变化 从反铁磁性到顺磁性 或反之亦然 的过渡发生在奈尔温度 这与居里温度类似 低于TC 高于TC铁磁性 顺磁性亚铁磁性 顺磁性反铁磁性 顺磁性材料中磁矩的方向 铁磁性 铁磁性材料中的磁矩 在没有施加磁场的情况下 磁矩是有序的且具有相同的大小 顺磁性 顺磁性材料中的磁矩 在没有施加磁场的情况下 这些磁矩是无序的 并且在施加的磁场的情况下有序 亚铁磁性 亚铁磁性材料中的磁矩 由于由两种不同的离子组成 磁矩相反地对齐并且具有不同的大小 这是在没有施加磁场的情况下 反铁磁性 反铁磁性材料中的磁矩 这些磁矩是相反的 并且具有相同的大小 这是在没有施加磁场的情况下 在居里温度下改变特性的具有磁矩的材料 编辑铁磁性 顺磁性 亚铁磁性和反铁磁性结构由固有磁矩组成 如果结构中的所有电子都配对 则由于它们的相反自旋和角动量 这些力矩会抵消 因此 即使施加磁场 这些材料也具有不同的性质 并且没有居里温度 6 7 顺磁性 编辑 主条目 顺磁性 当一些材料的温度高于居里点时 材料会表现出顺磁性 这样的材料叫顺磁性材料 当没有受到外部磁场的影响时 顺磁性材料不会表现磁性 反之则会表现磁性 没有受到外部磁场影响时 材料内部的磁矩是无序排列的 也就是说 材料内部的粒子不整齐且没有顺磁力线方向排列 当受到磁场影响时 这些磁矩会顺磁场线整齐排列 8 9 10 并且产生感应磁场 10 11 对于顺磁性 这种对外加磁场的响应是正的 称为磁化率 6 磁化率仅适用于居里温度以上的无序状态 12 顺磁性的来源 具有居里温度的材料 包括 13 全部含有未配对电子的原子 内电子层未被完全填充的原子 自由基 金属 超過居禮溫度後 原子被激發 旋轉的方向變成隨機的 7 不過可以被作用場重新調整 即材料变为顺磁性 在居里温度以下 材料的固有结构经历了一次相变相变 14 原子变为有序 材料具有铁磁性 10 与铁磁性材料的磁场相比 顺磁性材料的感应磁场非常弱 14 铁磁性 编辑 主条目 铁磁性 材料仅在其相应的居里温度以下具有铁磁性 在没有外加磁场的情况下 铁磁材料具有磁性 当没有外加磁场时 材料具有自发磁化 英语 Spontaneous magnetization 这是有序磁矩的结果 也就是说 对于铁磁性材料 原子具有某种对称性并且在同一方向上排列 从而产生永久磁场 磁性相互作用通过交换相互作用结合在一起 否则 热无序将克服磁矩的弱相互作用 交换相互作用的平行电子占据同一时间点的可能性为零 这意味着材料中会有一个倾向的平行排列 15 在这个过程中 玻尔兹曼因子贡献很大 因为它倾向于使相互作用的粒子在同一方向上排列 16 这会导致铁磁体具有较强的磁场和较高的居里温度 约 1000K 730 17 在居里温度以下 原子有序排列 从而导致自发磁性 材料具有铁磁性 在居里温度以上 该材料是顺磁性的 因为当该材料经历相变时 原子会失去其有序的磁矩 14 亚铁磁性 编辑 主条目 亚铁磁性材料仅在其相应的居里温度以下具有亚铁磁性 在没有外加磁场的情况下 亚铁磁材料具有磁性 并由两种不同离子组成 18 当没有外加磁场时 材料具有自发磁化 这是有序磁矩的结果 也就是说 对于亚铁磁性材料 一种离子的磁矩对准一个方向 有一个大小 另一种离子的磁矩对准相反方向 有一个不同的大小 因为磁矩在相反的方向有着不同的大小 所以仍然有自发磁化 存在磁场 18 和铁磁性材料相似 磁性相互作用通过交换相互作用结合在一起 但是 磁矩的方向是反平行的 导致净势是一个减另一个 18 低于居里点时 每个离子的原子都反平行对齐 有着不同的磁矩 造成自发磁化 材料具有亚铁磁性 高于居里点时 该材料是顺磁性的 因为当该材料经历相变时 原子会失去其有序的磁矩 18 反铁磁性与奈尔温度 编辑 主条目 反铁磁性 材料仅在其相应的奈尔温度以下具有反铁磁性 这与居里温度相似 高于奈尔温度时 该材料经历相变 变成顺磁性 也就是说 热能变得足够大 足以破坏材料内的微观磁有序性 19 它以路易 奈尔 Louis Neel 1904 2000 年 的名字命名 他因在该领域的工作而获得了 1970 年的诺贝尔物理学奖 材料有方向相反的相等磁矩 导致在奈尔温度以下磁矩为零和净磁性为零 反铁磁性材料在有或没有外加磁场的情况下有很弱的磁性 与铁磁性材料相似 磁性相互作用通过交换相互作用结合在一起 否则 热无序将克服磁矩的弱相互作用 15 20 奈尔温度时无序出现 20 下面列表中有几种物质的奈尔温度 21 Substance Neel temperature K MnO 116MnS 160MnTe 307MnF2 67FeF2 79FeCl2 24FeI2 9FeO 198FeOCl 英语 Iron oxychloride 80CrCl2 25CrI2 12CoO 291NiCl2 50NiI2 75NiO 525KFeO2 983 22 Cr 308Cr2O3 307Nd5Ge3 50已隱藏部分未翻譯内容 歡迎參與翻譯 居里 韦斯定律 编辑 主条目 居里 韦斯定律 The Curie Weiss law is an adapted version of 居里定律 The Curie Weiss law is a simple model derived from a mean field approximation this means it works well for the materials temperature T much greater than their corresponding Curie temperature TC i e T TC however fails to describe the magnetic susceptibility x in the immediate vicinity of the Curie point because of local fluctuations between atoms 23 Neither Curie s law nor the Curie Weiss law holds for T lt TC Curie s law for a paramagnetic material 24 x M H M m 0 B C T displaystyle chi frac M H frac M mu 0 B frac C T Definitionx the magnetic susceptibility the influence of an applied magnetic field on a materialM the magnetic moments per unit volumeH the macroscopic magnetic fieldB the magnetic fieldC the material specific Curie constantC m 0 m B 2 3 k B N A g 2 J J 1 displaystyle C frac mu 0 mu mathrm B 2 3k mathrm B N A g 2 J J 1 25 N A displaystyle N A Avagadro常数µ0 the permeability of free space Note in CGS units is taken to equal one 26 g the Lande g factorJ J 1 the eigenvalue for eigenstate J2 for the stationary states within the incomplete atoms shells electrons unpaired µB the Bohr MagnetonkB Boltzmann s constanttotal magnetism is N number of magnetic moments per unit volumeThe Curie Weiss law is then derived from Curie s law to be x C T T C displaystyle chi frac C T T mathrm C where T C C l m 0 displaystyle T mathrm C frac C lambda mu 0 l 是Weiss分子场常数 25 27 For full derivation see 居里 韦斯定律 物理 编辑 从上方接近居里温度 编辑 As the Curie Weiss law is an approximation a more accurate model is needed when the temperature T approaches the material s Curie temperature TC Magnetic susceptibility occurs above the Curie temperature An accurate model of critical behaviour for magnetic susceptibility with critical exponent g x 1 T T C g displaystyle chi sim frac 1 T T mathrm C gamma The critical exponent differs between materials and for the mean field model is taken as g 1 28 As temperature is inversely proportional to magnetic susceptibility when T approaches TC the denominator tends to zero and the magnetic susceptibility approaches infinity allowing magnetism to occur This is a spontaneous magnetism which is a property of ferromagnetic and ferrimagnetic materials 29 30 从下方接近居里温度 编辑 Magnetism depends on temperature and spontaneous magnetism occurs below the Curie temperature An accurate model of critical behaviour for spontaneous magnetism with critical exponent b M T T C b displaystyle M sim T T mathrm C beta The critical exponent differs between materials and for the mean field model as taken as b 1 2 where T TC 28 The spontaneous magnetism approaches zero as the temperature increases towards the materials Curie temperature 接近绝对零度 0开尔文 编辑 The spontaneous magnetism occurring in ferromagnetic ferrimagnetic and antiferromagnetic materials approaches zero as the temperature increases towards the material s Curie temperature Spontaneous magnetism is at its maximum as the temperature approaches 0 K 31 That is the magnetic moments are completely aligned and at their strongest magnitude of magnetism due to no thermal disturbance In paramagnetic materials temperature is sufficient to overcome the ordered alignments As the temperature approaches 0 K the 熵 decreases to zero that is the disorder decreases and becomes ordered This occurs without the presence of an applied magnetic field and obeys the 热力学第三定律 15 Both Curie s law and the Curie Weiss law fail as the temperature approaches 0 K This is because they depend on the magnetic susceptibility which only applies when the state is disordered 32 硫酸钆 continues to satisfy Curie s law at 1 K Between 0 and 1 K the law fails to hold and a sudden change in the intrinsic structure occurs at the Curie temperature 33 Ising相变模型 编辑 The Ising model is mathematically based and can analyse the critical points of phase transitions in ferromagnetic order due to spins of electrons having magnitudes of 1 2 The spins interact with their neighbouring dipole electrons in the structure and here the Ising model can predict their behaviour with each other 34 35 This model is important for solving and understanding the concepts of phase transitions and hence solving the Curie temperature As a result many different dependencies that affect the Curie temperature can be analysed For example the surface and bulk properties depend on the alignment and magnitude of spins and the Ising model can determine the effects of magnetism in this system Weiss磁畴和表面和体积居里温度 编辑 Materials structures consist of intrinsic magnetic moments which are separated into domains called Weiss domains 36 This can result in ferromagnetic materials having no spontaneous magnetism as domains could potentially balance each other out 36 The position of particles can therefore have different orientations around the surface than the main part bulk of the material This property directly affects the Curie temperature as there can be a bulk Curie temperature TB and a different surface Curie temperature TS for a material 37 This allows for the surface Curie temperature to be ferromagnetic above the bulk Curie temperature when the main state is disordered i e Ordered and disordered states occur simultaneously 34 The surface and bulk properties can be predicted by the Ising model and electron capture spectroscopy can be used to detect the electron spins and hence the magnetic moments on the surface of the material An average total magnetism is taken from the bulk and surface temperatures to calculate the Curie temperature from the material noting the bulk contributes more 34 38 The angular momentum of an electron is either ħ 2 or ħ 2 due to it having a spin of 1 2 which gives a specific size of magnetic moment to the electron the Bohr magneton 39 Electrons orbiting around the nucleus in a current loop create a magnetic field which depends on the Bohr Magneton and magnetic quantum number 39 Therefore the magnetic moments are related between angular and orbital momentum and affect each other Angular momentum contributes twice as much to magnetic moments than orbital 40 For terbium which is a rare earth metal and has a high orbital angular momentum the magnetic moment is strong enough to affect the order above its bulk temperatures It is said to have a high anisotropy on the surface that is it is highly directed in one orientation It remains ferromagnetic on its surface above its Curie temperature while its bulk becomes ferrimagnetic and then at higher temperatures its surface remains ferrimagnetic above its bulk Neel Temperature before becoming completely disordered and paramagnetic with increasing temperature The anisotropy in the bulk is different from its surface anisotropy just above these phase changes as the magnetic moments will be ordered differently or ordered in paramagnetic materials 37 更改材料的居里温度 编辑 Composite materials 编辑 Composite materials that is materials composed from other materials with different properties can change the Curie temperature For example a composite which has silver in it can create spaces for oxygen molecules in bonding which decreases the Curie temperature 41 as the crystal lattice will not be as compact The alignment of magnetic moments in the composite material affects the Curie temperature If the materials moments are parallel with each other the Curie temperature will increase and if perpendicular the Curie temperature will decrease 41 as either more or less thermal energy will be needed to destroy the alignments Preparing composite materials through different temperatures can result in different final compositions which will have different Curie temperatures 42 Doping a material can also affect its Curie temperature 42 The density of nanocomposite materials changes the Curie temperature Nanocomposites are compact structures on a nano scale The structure is built up of high and low bulk Curie temperatures however will only have one mean field Curie temperature A higher density of lower bulk temperatures results in a lower mean field Curie temperature and a higher density of higher bulk temperature significantly increases the mean field Curie temperature In more than one dimension the Curie temperature begins to increase as the magnetic moments will need more thermal energy to overcome the ordered structure 38 Particle size 编辑 The size of particles in a material s crystal lattice changes the Curie temperature Due to the small size of particles nanoparticles the fluctuations of electron spins become more prominent this results in the Curie temperature drastically decreasing when the size of particles decrease as the fluctuations cause disorder The size of a particle also affects the anisotropy causing alignment to become less stable and thus lead to disorder in magnetic moments 34 43 The extreme of this is superparamagnetism which only occurs in small ferromagnetic particles and is where fluctuations are very influential causing magnetic moments to change direction randomly and thus create disorder The Curie temperature of nanoparticles are also affected by the crystal lattice structure body centred cubic bcc face centred cubic fcc and a hexagonal structure hcp all have different Curie temperatures due to magnetic moments reacting to their neighbouring electron spins fcc and hcp have tighter structures and as a results have higher Curie temperatures than bcc as the magnetic moments have stronger effects when closer together 34 This is known as the coordination number which is the number of nearest neighbouring particles in a structure This indicates a lower coordination number at the surface of a material than the bulk which leads to the surface becoming less significant when the temperature is approaching the Curie temperature In smaller systems the coordination number for the surface is more significant and the magnetic moments have a stronger affect on the system 34 Although fluctuations in particles can be minuscule they are heavily dependent on the structure of crystal lattices as they react with their nearest neighbouring particles Fluctuations are also affected by the exchange interaction 43 as parallel facing magnetic moments are favoured and therefore have less disturbance and disorder therefore a tighter structure influences a stronger magnetism and therefore a higher Curie temperature Pressure 编辑 Pressure changes a material s Curie temperature Increasing pressure on the crystal lattice decreases the volume of the system Pressure directly affects the kinetic energy in particles as movement increases causing the vibrations to disrupt the order of magnetic moments This is similar to temperature as it also increases the kinetic energy of particles and destroys the order of magnetic moments and magnetism 44 Pressure also affects the density of states DOS 44 Here the DOS decreases causing the number of electrons available to the system to decrease This leads to the number of magnetic moments decreasing as they depend on electron spins It would be expected because of this that the Curie temperature would decrease however it increases This is the result of the exchange interaction The exchange interaction favours the aligned parallel magnetic moments due to electrons being unable to occupy the same space in time 15 and as this is increased due to the volume decreasing the Curie temperature increases with pressure The Curie temperature is made up of a combination of dependencies on kinetic energy and the DOS 44 The concentration of particles also affects the Curie temperature when pressure is being applied and can result in a decrease in Curie temperature when the concentration is above a certain percent 44 Orbital ordering 编辑 Orbital ordering changes the Curie temperature of a material Orbital ordering can be controlled through applied strains 45 This is a function that determines the wave of a single electron or paired electrons inside the material Having control over the probability of where the electron will be allows the Curie temperature to be altered For example the delocalised electrons can be moved onto the same plane by applied strains within the crystal lattice 45 The Curie temperature is seen to increase greatly due to electrons being packed together in the same plane they are forced to align due to the exchange interaction and thus increases the strength of the magnetic moments which prevents thermal disorder at lower temperatures 铁电材料中的居里温度 编辑 In analogy to ferromagnetic and paramagnetic materials the term Curie temperature TC is also applied to the temperature at which a ferroelectric material transitions to being paraelectric Hence TC is the temperature where ferroelectric materials lose their spontaneous polarisation as a first or second order phase change occurs In case of a second order transition the Curie Weiss temperature T0 which defines the maximum of the dielectric constant is equal to the Curie temperature However the Curie temperature can be 10 K higher than T0 in case of a first order transition 46 Figure 4 Below T0 Ferroelectric polarisation P in an applied electric field E Figure 5 Above T0 Dielectric polarisation P in an applied electric field E Below TC Above TC 47 Ferroelectric Dielectric paraelectric Antiferroelectric Dielectric paraelectric Ferrielectric Dielectric paraelectric Helielectric Dielectric paraelectric Ferroelectric and dielectric 编辑 Materials are only ferroelectric below their corresponding transition temperature T0 48 Ferroelectric materials are all pyroelectric and therefore have a spontaneous electric polarisation as the structures are unsymmetrical Ferroelectric materials polarization is subject to hysteresis Figure 4 that is they are dependent on their past state as well as their current state As an electric field is applied the dipoles are forced to align and polarisation is created when the electric field is removed polarisation remains The hysteresis loop depends on temperature and as a result as the temperature is increased and reaches T0 the two curves become one curve as shown in the dielectric polarisation Figure 5 49 相对介电常数 编辑 A modified version of the Curie Weiss law applies to the dielectric constant also known as the relative permittivity 46 50 ϵ ϵ 0 C T T 0 displaystyle epsilon epsilon 0 frac C T T mathrm 0 应用 编辑 A heat induced ferromagnetic paramagnetic transition is used in magneto optical storage media for erasing and writing of new data Famous examples include the Sony Minidisc format as well as the now obsolete CD MO format Curie point electro magnets have been proposed and tested for actuation mechanisms in passive safety systems of fast breeder reactors where control rods are dropped into the reactor core if the actuation mechanism heats up beyond the material s curie point 51 Other uses include temperature control in soldering irons 52 and stabilizing the magnetic field of tachometer generators against temperature variation 53 参见 编辑铁电性 居里定律参考资料 编辑引用 编辑 Buschow 2001 p5021 table 1 Jullien amp Guinier 1989 第155頁 Kittel 1986 Hall amp Hook 1994 第200頁 Jullien amp Guinier 1989 第136 38頁 6 0 6 1 Ibach amp Luth 2009 7 0 7 1 Levy 1968 第236 39頁 Dekker 1958 第217 20頁 Levy 1968 10 0 10 1 10 2 Fan 1987 第164 65頁 Dekker 1958 第454 55頁 Mendelssohn 1977 第162頁 Levy 1968 第198 202頁 14 0 14 1 14 2 Cusack 1958 第269頁 15 0 15 1 15 2 15 3 Hall amp Hook 1994 第220 21頁 Palmer 2007 Hall amp Hook 1994 第220頁 18 0 18 1 18 2 18 3 Jullien amp Guinier 1989 第158 59頁 Spaldin Nicola A Magnetic materials fundamentals and device applications Repr Cambridge Cambridge Univ Press 2006 89 106 ISBN 9780521016582 20 0 20 1 Jullien amp Guinier 1989 第156 57頁 Kittel Charles Introduction to Solid State Physics 8th New York John Wiley amp Sons 2005 ISBN 978 0 471 41526 8 Ichida Toshio Mossbauer Study of the Thermal Decomposition Products of K2FeO4 Bulletin of the Chemical Society of Japan 1973 46 1 79 82 doi 10 1246 bcsj 46 79 Jullien amp Guinier 1989 第153頁 Hall amp Hook 1994 第205 06頁 25 0 25 1 Levy 1968 第201 02頁 Kittel 1996 第444頁 Myers 1997 第334 45頁 28 0 28 1 Hall amp Hook 1994 第227 28頁 Kittel 1986 第424 26頁 Spaldin 2010 第52 54頁 Hall amp Hook 1994 第225頁 Mendelssohn 1977 第180 81頁 Mendelssohn 1977 第167頁 34 0 34 1 34 2 34 3 34 4 34 5 Bertoldi Bringa amp Miranda 2012 Brout 1965 第6 7頁 36 0 36 1 Jullien amp Guinier 1989 第161頁 37 0 37 1 Rau Jin amp Robert 1988 38 0 38 1 Skomski amp Sellmyer 2000 39 0 39 1 Jullien amp Guinier 1989 第138頁 Hall amp Hook 1994 41 0 41 1 Hwang et al 1998 42 0 42 1 Paulsen et al 2003 43 0 43 1 Lopez Dominguez et al 2013 44 0 44 1 44 2 44 3 Bose et al 2011 45 0 45 1 Sadoc et al 2010 46 0 46 1 Webster 1999 Kovetz 1990 第116頁 Myers 1997 第404 05頁 Pascoe 1973 第190 91頁 Webster 1999 第6 55 6 56頁 Takamatsu Demonstration of Control Rod Holding Stability of the Self Actuated Shutdown System in Joyo for Enhancement of Fast Reactor Inherent Safety Journal of Nuclear Science and Technology TMT 9000S Pallas Areny amp Webster 2001 第262 63頁 来源 编辑 Buschow K H J Encyclopedia of Materials Science and Technology Elsevier 2001 ISBN 0 08 043152 6 Kittel Charles Introduction to Solid State Physics 6th John Wiley amp Sons 1986 ISBN 0 471 87474 4 Pallas Areny Ramon Webster John G Sensors and Signal Conditioning 2nd John Wiley amp Sons 2001 ISBN 978 0 471 33232 9 Spaldin Nicola A Magnetic Materials Fundamentals and Applications 2nd Cambridge Cambridge 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2014 14 March 2013 原始内容存档于2018 08 10 TMT 9000S Soldering and Rework Station thermaltronics com 13 January 2016 原始内容存档于2017 12 21 取自 https zh wikipedia org w index php title 居里点 amp oldid 75549427, 维基百科,wiki,书籍,书籍,图书馆,

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