High-Pressure and low-temperature Mossbauer Spectroscopy

金刚石砧细胞高压莫斯巴勒光谱是研究材料在压力下的性质，特别是磁性能的有力方法之一。在本项目中，我们对典型的氧化铁材料在高压和低温下进行了Fe穆斯堡尔测量，以阐明高压下的磁性能。本项目取得的成果总结如下：(1)钙钛矿氧化铁SrFeO_3和caFeO_3：由于这些氧化铁具有异常高的铁价，因此研究高压对这些氧化物电子结构的影响是很有意义的。我们发现随着外部压力的增加，尼尔温度有明显的增加。当温度达到77 GPa时，SrFeO_3没有发生任何结构转变。在高压作用下，磁性结构由螺旋自旋转变为共线铁磁结构。另一方面，CaFeO_3在外部高压作用下发生了结构转变和自旋交叉过渡，由高自旋态向低自旋态转变。(2)磁铁矿，Fe_3O_4：磁铁矿是已知最古老的磁性材料，我们发现高压相出现在29gpa。该高压磁铁矿具有2个非等效铁位，其数量比为1:2，在300k时为准磁性（或非磁性）。(3)乌氏体，Fe_< 1-3>O：高达80 gPa高压^<57>，使用Fe_<0.977>O的样品进行了Fe Mossbauer研究，这是最接近化学计量的成分。我们发现压力和300 K时48 T的超强磁超细磁场使Neel温度明显升高。(4)利用同步辐射的高压穆斯堡尔谱成功地观测到了SrFeO_3在44 GPa和74 GPa的300 K下的核共振前向散射。DAC可以为我们提供一个非常高压的场，但是样品应该被限制在一个非常小的数量，通常很难得到一个高质量的光谱。为了消除测量难度，我们对测量条件进行了优化，得到了高质量的光谱。然而，在4.2 K和300 K之间的低温测量才刚刚开始使用液氦晶体，在4.2 K和300 K之间的低温测量才刚刚开始使用液氦晶体，为了完成DAC的高压和低温测量，必须继续这项研究项目。少

It is well recognized that the high-pressure Mossbarer spectroscopy using a diamond anvil cell is one of powerful methods to elucidate the material properties under pressure, especially for the magnetic properties. In this project, we have performed the Fe Mossbauer measurements under high-pressure and low temperature for the typical iron oxides meterials in order to elucidate the magnetic properties under high-pressure. Results obtained in this project are summarized as follows.(1) Perovskite iron oxides, SrFeO_3 and caFeO_3 : Since these iron oxides have an abnormally high valence as Fe, it is intresting to investigate the effects of high pressure on the electronic stucture of these exides. We found the appreciable increases of the Neel temperatures as an increase of the external pressure. SrFeO_3 did not show any structural trasformation up to 77 GPa. However the magnetic stucture changes form helical-spin to colinear ferromagnetic structure by the external high pressure. On the oth … More er hand, CaFeO_3 shows the structural transformation and simultaneously the spin-cross-over transition from high-spin to low-spin state by the external high-pressure. (2) Magnetite, Fe_3O_4 : Magnetite is the oldest known magnetic naterial and we have found that the high pressure phase appeared at 29 GPa. This high-pressure magnetite has 2 non-equivalent iron sites whose number ratio is 1 : 2 and they are para-(or non-) magnetic at 300 K.(3) Wustite, Fe _<1-3>O : Up to 80 gPa high-pressure ^<57>Fe Mossbauer investigation has been performed using a specimen Fe_<0.977>O which is the closest composition to the stoichiometry. We found the appreciable increase of the Neel temperature by the pressure and an extraordinary large magnetic hyperfine nagnetic field of 48 T at 300 K.(4) High-pressure Mossbauer spectroscopy using a synchrotron radiation : Muclear resonance forward scattering has been successfully obserbed for SrFeO_3 at 44 GPa and 74 GPa at 300 K.DAC can offer us a very high-pressure field, but the specimen should be restricted to be an extremely small amounts and usually it is rather difficult to get a spectrum having a good-quality. In order to eliminate the difficulty for the measurements, we optimexed the measurement conditions and can get a high-quality spectrum. However, the measurements at low temperatures between 4.2 K and 300 k have just begun using a liquid-helium cryastat and it is measurements at liw temperatures between 4.2 K and 300 K have just begun using a liquid-helium cryastat and it is essential to continue this research project in order to accomplish the high-pressure and low-temperature measurements by DAC. Less