螺旋磁性是一種相鄰磁矩的自旋以螺旋模式進行排列的磁序形式,其特徵轉角介於0到180度之間。這種現象是鐵磁反鐵磁交換相互作用之間競爭的結果,也可以分別將鐵磁和反鐵磁視為具有0度和180度特徵轉角的螺旋磁結構。螺旋磁序本質上可以是左旋或右旋的,因此螺旋磁序破壞了空間反演對稱性

90K下鍺化鐵(FeGe)中螺旋自旋條紋的洛倫茲TEM圖像

嚴格來說,螺旋磁體並沒有永久磁矩,因此有時被認為是一種複雜的反鐵磁體。而錐形磁性除了具有螺旋調製外還有永久磁矩(例如,金屬鈥在低於20K時表現出錐形磁性[1])。是否具有永久磁矩可以將螺旋磁體與錐形磁體區分開來。

螺旋磁性的概念於1959年首次提出,它可以作為對二氧化錳磁結構的解釋[2]。螺旋磁性最初應用於中子衍射,後來發現它可以被洛倫茲電子顯微鏡更直接地觀察到[3]。據報道,大部分材料在低溫下表現出螺旋磁性,然而也有一些螺旋磁結構可以在室溫下保持穩定[4]。許多螺旋磁體具有手性立方結構,例如B20晶體結構類型。

就像普通鐵磁體具有分隔各個磁疇的疇壁一樣,螺旋磁體也有自己的以拓撲電荷為特徵的疇壁。 [5]

螺旋磁材料
材料 溫度範圍
β-MnO2 [2][6] < 93 K
FeGe, [4] < 278 K
MnGe[7] < 170 K
MnSi, [8] < 29 K
FexCo1−xSi (0.3 ≤ x ≤ 0.85) [9] [10]
Cu2OSeO3[11] < 58 K
Tb[12] 219–231 K
Dy[13] 85–179 K
Ho[14] 20–132 K

參見

編輯

參考文獻

編輯
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