57Fe Mössbauer-effect studies of Ca-rich, Fe-bearing clinopyroxenes: Part II. Magnetic spectra of magnesian hedenbergite
57Fe Mössbauer-effect studies of Ca-rich, Fe-bearing clinopyroxenes: Part II. Magnetic spectra of magnesian hedenbergite
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DOI：
10.2138/am-2003-0722
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发表时间：
2003-07
影响因子：
3.1
通讯作者：
S. Eeckhout;E. De Grave
中科院分区：
文献类型：
--
作者：
S. Eeckhout;E. De Grave
摘要：采用透射57Fe Mössbauer光谱法，在4.2 ~ 35 K温度范围和4.2 K时60 kOe的纵向外场条件下，研究了两种铁含量略有不同的天然镁镁石（HED1和HED2）样品的磁性能。利用两个模型无关的超细场分布（一个是Fe2+的主要组分，另一个是Fe3+的弱组分）的叠加，对磁场零场Mössbauer谱（MS）进行了充分的细化，通过超细相互作用哈密顿量的对角化确定了每个组成元素子谱的8个吸收的位置和强度。Fe2+的最大概率饱和超精细场在HED1和HED2中分别为180 kOe和185 kOe，而Fe3+的最大概率饱和超精细场在~545 kOe。对于两种hedenberite样品，电场梯度（EFG）的Fe2+不对称参数h都很高，在0.7 ~ 0.8之间，与温度无关。铁磁超细场在EFG主轴框架内的取向为~（85°，38°），不受吸收器温度的影响。施加磁场Mössbauer谱表明，施加磁场不会破坏磁性结构，因此磁各向异性很强。考虑了超精细场相对于外场的大小和取向分布，用双参数分布模型对光谱进行了满意的描述。所得的超精细参数与零场光谱结果吻合良好。超细场的温度依赖性似乎表明，hedenbergite中的磁性结构可以用二维矩形Ising模型来近似，并且链间和链内的磁性交换相互作用的大小相似。
Abstract The magnetic properties of two natural magnesian hedenbergite samples with slightly different Fe contents (hereafter denoted HED1 and HED2) were studied by transmission 57Fe Mössbauer spectroscopy within the temperature range 4.2-35 K and in a longitudinal, external field of 60 kOe at 4.2 K. The magnetic zero-field Mössbauer spectra (MS) were adequately refined using a superposition of two model-independent hyperfine-field distributions, one for the dominant Fe2+ component and one for the weak Fe3+ contribution, the positions of the eight absorptions and their intensities for each composing elemental subspectrum being determined by diagonalization of the hyperfine-interaction Hamiltonian. The maximum-probability saturation hyperfine fields for Fe2+ were found to be 180 kOe and 185 kOe for HED1 and HED2, respectively, while a value of ~545 kOe was obtained for Fe3+. For both hedenbergite samples, the Fe2+ asymmetry parameter h of the electric field gradient (EFG) is quite high, namely 0.7-0.8 regardless of temperature. The orientation of the ferrous magnetic hyperfine field in the EFG principal-axes frame is ~(85°, 38°) and is not affected by the temperature of the absorber. The applied-field Mössbauer spectra show that the applied field does not disrupt the magnetic structure, and consequently that magnetic anisotropy is quite strong. The spectra were satisfactorily described by a two-parameter distribution model, taking into account distributions for the magnitude and the orientation of the hyperfine field with respect to the external field. The obtained hyperfine parameters are in excellent agreement with the results from the zerofield spectra. The temperature dependence of the hyperfine field seems to indicate that the magnetic structure in hedenbergite can be approximated by a two-dimensional rectangular Ising model and that the inter-chain and intra-chain magnetic exchange interactions are of similar magnitude.