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A two-dimensional layered manganese(Ⅱ) pyrophosphate, [NH4]2[Mn3(P2O7)2(H2O)2] (1), has been synthesized hydrothermally. Its structure is determined by single-crystal X-ray diffraction analysis. Its structure is built up by MnO6 octahedra and P2O7 units, with ammonium NH4+ cations residing in the interlayer regions. The manganese pyrophosphate layer consists of infinite chains of cis and trans edge sharing MnO6 octahedra linked by P2O7 units. Magnetic susceptibility measurements show that this compound exhibits ferrimagnetic-like ordering below 3.2 K. Further study shows that there are two possible superexchange pathways via the oxygen anions in Mn2+ ions. Owing to the different bridging modes of O2-, the competition between ferromagnetic interactions and antiferromagnetic interactions in Mn2+ ions results in the ferrimagnetic behavior of 1. 相似文献
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ZHAOTong-Yun SHENBao-Gen ZHANGShao-Ying YAOJin-Lei ZHANGLi-Gang LIYun-Bao 《中国物理快报》2003,20(6):912-914
Magnetic transitions and magnetoresistance of HfFe6Ge6-type Y1-xDyxMn6Sn6 (x=0.2 and 0.3) have been investigated in the temperature range of 5-380K. It was found that the strong exchange interaction between the Dy and Mn sublattices results in incomplete ferromagnetism at low temperatures. At higher temperatures, the metamagnetic transition from an antiferromagnetic state to a ferrimagnetic state can be induced by a fairly small threshold field or by increasing temperature. The magnetic transition is accompanied by a large magnetoresistance effect of about -29% and -16% at 5K for x=0.2 and 0.3, respectively. 相似文献
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利用密度矩阵重整化群(DMRG)方法研究磁性阻挫对一种S=1/2准一维反铁磁自旋链但却具有亚铁磁性的Heisenberg系统基态的影响.计算了单个晶胞的基态能、自旋关联函数以及自旋能隙.研究表明这种Heisenberg自旋系统的基态随着阻挫α的增强将从磁有序相变化到自旋无序相,并且伴随着自旋能隙的出现,量子相变点为α≈0.412.同时线形链上格点间自旋长程关联值的计算结果表明在磁有序区间体系的磁有序性质随着α的增强而减弱,阻挫在0≤α< 相似文献
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通过水热合成得到石榴石型铁氧体材料Nd3-xSrxFe5O12(x=0.2,0.4,0.6,0.8),经X射线粉末衍射分析确定样品属于立方晶系,Ia3d空间群,晶格常数a>1.2600 nm.Mssbauer谱数据显示Sr2+离子和Nd3+离子共同占据十二面体C位,晶格中有少量Fe4+离子生成.通过扫描电子显微镜观察到样品晶粒为菱形十二面体.高温M-T曲线和磁滞回线表明,4个样品的居里温度均在570 K左右,不因Sr2+离子含量不同而改变;但是随着Sr2+离子在晶格中含量的增加,样品的饱和磁化强度(Ms)下降,矫顽力(Hc)增大. 相似文献
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LIU Lei YAN Shi-Lei 《理论物理通讯》2005,44(4):743-748
We study the ferrimagnetic properties of spin 1/2 and spin-1 systems by means of the effective field theory. The system is considered in the framework of bond dilution mixed Blume-Capel mode/ (BCM) with random single-ion anisotropy. The investigation of phase diagrams and magnetization curves indicates the existence of induced magnetic ordering and single or multi-compensation points. Special emphasis is placed on the influence of bond dilution and random single-ion anisotropy on normal or induced magnetic ordering states and single or multi-compensation points. Normal magnetic ordering states take on new phase diagrams with increasing randomness (bond and anisotropy), while anisotropy induced magnetic ordering states are always occurrence no matter whether concentration of anisotropy is large or small. Existence and disappearance of compensation points rely strongly on bond dilution and random singleion anisotropy. Some results have not been revealed in previous papers and predicted by Néel theory of ferrimagnetism. 相似文献
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The present study reports the magnetizations and magneto-transport properties of PrFel_xNixO3 thin films grown by pulsed laser ablation technique on LaA103 snbstrates. From DC M/H plots of these films, weak ferromagnetism or ferrimagnetism behaviors are observed. With Ni substitution, reduction in saturation magnetization is also seen. With Ni doping, variations in saturation field (Hs), coercive field (Hc), Weiss temperature (0), and effective magnetic moment (Pelf) are seen. A small change of magnetoresitance with application of higher field is observed. Various essential parameters like density of state (Nf) at Fermi level, Mott's characteristic temperature (To), and activation energy (Ea) in the presence of and in the absence of magnetic field are calculated. The present observed magnetic properties are related to the change of Fe-O bond length (causing an overlap between the oxygen p orbital and iron d orbital) and the deviation of the Fe-O-Fe angle from 180~. Reduction of magnetic domain after Ni doping is also explored to explain the present observed magnetic behavior of the system. The influence of doping on various transport properties in these thin films indicates a distortion in the lattice structure and single particle band width, owing to stress-induced reduction in unit cell volume. 相似文献
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