我們研究了LaMn2Si2和LaMnCuSi2的磁化特性。就LaMn2Si2而言，我們的實驗結果跟中子繞射與梅思堡量測的結果一致。在量測LaMn2Si2的直流零磁冷卻(Zreo-field cooling，ZFC)磁化強度 MZFC和磁冷卻(Field cooling，FC)磁化強度 MFC中，我們發現在0.1 kOe的磁場下，MZFC會在305K時開始跟MFC分開。但在量測LaMn2Si2的交流磁化率 χac下，沒有發現到形成自旋玻璃態所需的峰值(peak)。因此，儘管零磁冷和磁冷之磁化強度會，但是無法在LaMn2Si2裡形成自旋玻璃相。當有 50% 的Mn離子被Cu離子所取代掉時，發現樣本內部產生了一個由磁場引導的磁序 (field induced magnetic order) 。當溫度下降，LaMnCuSi2從順磁相變成一個(高溫)反鐵磁相，接著再變為傾斜鐵磁相(canted-ferromagnetic phase) ，最後形成(低溫)反鐵磁相。 當頻率為10 kHz 時， LaMnCuSi2交流磁化率裡的實部在 79 K有一峰值，其虛部也在63 K顯現一峰值。交流磁化率中的實部或虛部隨溫度的變化都明顯地與頻率有關，這顯示了LaMnCuSi2中自旋玻璃跟反鐵磁相的共存。 溫度為250 K時，兩者都有一小小的突起區塊。 最後我們也給出LaMnCuSi2在外加磁場下的磁相圖。

We have studied the magnetic properties of LaMn2Si2 and LaMnCuSi2. For LaMn2Si2, our measurements are consistent with the results of neutron diffraction and Mössbauer. For the dc-magnetization measurements of LaMn2Si2, MZFC(T) starts to deviate from MFC(T) at ~305 K in a magnetic field of 0.1 kOe. There is no cusp observed in the real or imaginary component of the ac-susceptibility for LaMn2Si2. Therefore, despite the deviation from MZFC(T) to MFC(T) , there is no spin-glass phase in LaMn2Si2. While 50% of Mn ions are replaced by Cu ions, there is a magnetic-field-induced antiferromagnetic order in LaMnCuSi2. As the temperature is decreasing, the magnetic phase of LaMnCuSi2 changes from a paramagnetic to an (high-temperature) antiferromagnetic, then to a canted ferromagnetic, and finally to an (low-temperature) antiferromagnetic phase. There is a peak at ~ 79 K (for 10000 Hz) in real (X’) and at ~ 63 K (for 10000 Hz) in imaginary (X”) component of ac susceptibility for LaMnCuSi2. Either X’ or X” significantly depends on the frequency, which suggest a coexistence of spin-glass and antiferromagnetic phase in LaMn2Si2. The sketch of phase diagram for LaMnCuSi2 is provided.

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