Magnetism,spin relaxation and hyperfine interactions of rare earths in RM6Al6(M = Cr,Mn, Cu)

The systems RM₆Al₆ (R = rare earth or Y, M = Cr, Mn, Cu, Rh) were studied by magnetization measurements and by Mossbauer spectroscopy of ¹⁵⁵Gd, ¹⁶¹Dy, ¹⁶⁶Er and ¹⁷⁰Yb. The magnetization studies show weak R-R antiferromagnetic exchange interactions in RCu₆Al₆(T_n)Gd) = 21 K, less than 4 K for all other R and strong crystalline field effects. Similar phenomena are observed in RMn₆Al₆ and RCr₆Al₆, however, due to the presence of a Mn or Cr local moment the systems order ferrimagnetically. In RCr₆Al₆the order temperatures are low T_c ～ 25 K, yet T_c(GdCr₆Al₆) = 170 K. The Mossbauer studies observations are consistent with the magnetiza results. In the case where Er and Yb are not ordered at 4.1 K, the spectra still show magnetic hyperfine structure however of paramagnetic nature. The spectra yield the hyperfine interaction spin Hamiltonian parameters and the spin relaxation rates. These turn out to be extremely slow (1O⁸–1O⁹ sec^?1, a very uncommon phenomenon for a concentrated Er or Yb metallic system.     

151Eu-Mössbauer study of pressure-induced valence transitions in EuM2Ge2 (M=Ni,Pd,Pt)

¹⁵¹Eu-Mössbauer spectroscopy is used to study the ternary intermetallics EuM₂Ge₂ (M=Ni, Pd, Pt), in which Eu is divalent, and EuNi₂Si₂ as a trivalent reference system in the pressure range 0–31 GPa. In EuNi₂Ge₂ and EuPd₂Ge₂, one observes a valence transition from Eu²⁺ to Eu³⁺ around 5 and 25 GPa, accompanied by a change in isomer shift of 9.3 and 10.1 mm/s, respectively. These are the largest pressure-driven changes in isomer shift for¹⁵¹Eu-spectroscopy observed up to now.     

Hyperfine interactions in ultrafine amorphous Fe−M−B (M=Ni,Co) alloys

Ultrafine amorphous (Fe, Co, Ni) B powders have been prepared by a chemical reduction method. The influence of the Co and Ni atoms on the distribution of internal magnetic fields P(B_hf) has been investigated. The quadrupole splitting distribution P(QS) of ultrafine amorphous Fe−Ni−B powders has a form similar to that derived for the dense random packing of atoms.     

Comparison of the paramagnetic fluctuations in GdM2 and DyM2 (M=Al,Ni)

The muon spin relaxation in the paramagnetic states of GdNi₂ and DyNi₂ compounds has been measured, as a complement to earlier studies of the rare earth dialuminides (REAl₂). In addition, improved data have been taken on a GdAl₂-sample, up to a temperature of 4T_c. At high temperatures the Moriya molecular field model predicts a rare earth spin fluctuation rate proportional to the Curie temperature of the compund, which would lead to a T _c ⁻¹ dependence of the muon relaxation rate. This relation is fulfilled for the pair GdNi₂/GdAl₂, but not for the DyNi₂/DyAl₂ ratios. Possible reasons for this discrepancy are discussed.     

Thermal Expansion in Fe2MAl (M = Ti,V, Cr,Mn, Fe,Co, and Ni) Band Ferromagnets

Physics of the Solid State - The linear thermal expansion coefficients (LTEC) of semimetallic Fe2MAl (M = Ti, V, Cr, Mn, Fe, Co, and Ni) alloys have been measured in the temperature range...     

High-pressure 155Gd-Mössbauer study of magnetic properties in GdM2 Laves phases (M=Mn,Fe, Al)

Hyperfine Interactions - We report on high-pressure 155Gd-Mössbauer studies of the magnetic properties of GdM2 (Mn, Fe, Al) Laves phases in the cubic C15 phase, and, for the first time, of...     

Magnetism and hyperfine interactions of Fe, Eu, Gd, Dy, Er and Yb in RM4Al8 compounds (R = rare earth or Y, M = Cr, Mn, Fe, Cu)

Mössbauer and magnetic susceptibility studies of sixty tetragonal RM₄Al₈ compounds (R = 4f, M = 3d element), show a wide variety of magnetic phenomena in the behaviour of 3d transition elements. The rare earths order antiferromagnetically at temperatures below 10–30 K in all compounds. The 3d elements, however, all behave differently. Fe in RFe₄Al₈ has a localized moment (effective moment of 4.4 _μB) and orders independently of the rare earth sublattice. Mn in RMn₄Al₈ has also a localized moment (1 _μB) but orders only when the rare earths order. Cr in RCr₄Al₈ has no moment of its own, but it has an induced moment (.1 _μB) by its magnetic rare earth neighbours. Cu in RCu₄Al₈ is nonmagnetic. The Mössbauer studies of ¹⁵¹Eu, ¹⁵⁵Gd, ¹⁶¹Dy, ¹⁶⁶Er, ¹⁷⁰Yb and a ⁵⁷Fe probe yield all hyperfine interaction parameters including the orientation of the hyperfine field relative to the crystallographic c-axis. In addition, the studies yield the Ce, Eu and Yb valencies in the various compounds. Eu in EuFe₄Al₈ and in EuMn₄Al₈ and Yb in YbCr₄Al₈ are in a mixed valent state.     

M2Ge17(M=Ni、Mn)及其阴离子的稳定性和磁性研究

采用密度泛函理论（density functional theory,DFT）中的广义梯度近似（generalized gradient approximation,GGA）对Ni2Ge17,Mn2Ge17,[Ni2Ge17]4-和[Mn2Ge17]2-三种同分异构体的几何结构、电子结构和磁性进行了研究。通过对三种同分异构体的稳定性分析,得出D4d结构的[Ni2Ge17]4-最为稳定。由磁性的分析得到,Ni2Ge17和[Ni2Ge17]4-的D2d、D4d、D4h结构的磁矩均为零,体现为非磁性。对于Mn2Ge17和[Mn2Ge17]2-的D4d结构出现了自旋分裂能级,分别带有9μB 和8μB的磁矩。其中,Mn原子与Ge原子之间存在弱的铁磁相互作用。对于D4h结构的Mn2Ge17,带有7μB的磁矩,Mn原子和Ge原子之间既存在弱的铁磁相互作用又存在弱的反铁磁相互作用,而Mn2Ge17和[Mn2Ge17]2-的D2d结构以及[Mn2Ge17]2-的D4h结构的磁矩为零。     

Thermal Expansion of Co2MAl (M = Ti,V, Cr,Mn, Fe,Ni) Band Ferromagnets

Physics of the Solid State - The thermal expansion coefficient (TEC) of Co2MAl (M = Ti, V, Cr, Mn, Fe, Ni) band ferromagnets is measured in the temperature interval of 80–900 K. The...     

Mn(SiO2)3(M=Fe,Co,Ni;n=1-3)团簇的几何结构、光电性质及磁性

基于密度泛函理论中的广义梯度近似系统研究M_n(SiO₂)₃(M=Fe,Co,Ni;n=1-3)团簇的几何结构、光电性质和磁学性质.结果表明:Fe,Co原子相对于Ni原子更易于在(SiO₂)₃团簇上聚集;通过分析团簇的分裂途径及其产物,发现稳定性较好的氧化硅是一种很好的用于负载过渡金属"岛膜"的载体材料;M_n(SiO₂)₃团簇的能隙恰好位于近红外光谱范围内.通过磁性分析发现,该复合团簇的磁矩主要局域在过渡金属原子周围,而且,Fe₂(SiO₂)₃和Co₃(SiO₂)₃具有相对较大的磁矩,这主要源于过渡金属原子的d轨道间相互耦合.能隙和磁性两方面性质进一步肯定了二氧化硅磁性复合材料在医学界被用作光动力靶向治疗的可观前景.     

Anomalies in the behavior of the non-stoichiometric systems ZrMn2T0.8 (T = Mn,Fe, Co,Ni and Cu)

Unit cell dimensions and hydriding characteristics of the non-stoichiometric systems ZrMn₂T_0.8, with T = Mn, Fe, Co, Ni and Cu have been determined. Hydrides of these systems show plateau pressures at 25 C which vary in a systematic way with the atomic number of T, ranging from 0.3 (for T = Fe) to 4 atm (for T = Co). All of these plateau pressures are much greater than that of the hydride of stoichiometric ZrMn₂. There is a “Cobalt Effect” in that the plateau pressure of ZrMn₂Co_0.8 hydride is extraordinarily high and, moreover, the lattice dimensions of ZrMn₂Co_0.8 are small compared to ZrMn₂ and the other ternaries. The origin of the Co effect is as yet unclear. It may originate with the particulars of the site occupancies or special metallic bonding effects.     

Metallic magnetism in amorphous TM-Y (TM = Mn,Fe, Co,Ni) alloys

Systematic variations of magnetic properties in amorphous TM-Y (TM = Mn, Fe, Co, Ni) alloys are investigated on the basis of a finite temperature theory of amorphous metallic magnetism which takes into account both thermal spin fluctuations and the fluctuations due to structural and configurations disorder. It is shown that the magnetic phase diagrams calculated in the most random atomic configuration explain qualitatively the spinglass (SG) in Mn-Y, the SG ferromagnetism (F) transition in Fe-Y, and the F-paramagnetism transition in Co-Y and Ni-Y alloys. Magnetization vs concentration curves and susceptibility vs concentration curves as well as the effective Bohr magneton numbers are also shown to be explained qualitatively or semi-quantitatively by the theory. Their miscroscopic mechanisms are elucidated by means of their electronic structures, magnetic couplings, and atomic short range order. It is found that the magnetism in Fe-Y and Mn-Y amorphous alloys is strongly influenced by the atomic short range order. The result explains different magnetic phase diagrams in amorphous Fe-Y alloys and experimental SG transition temperatures in amorphous Mn-Y alloys.     

Tin-doped spinel-related oxides of composition M3O4 (M = Mn, Fe, Co)

Tin-doped compounds of spinel-related M₃O₄ (M = Fe, Mn, Co) have been studied by ¹¹⁹Sn and ⁵⁷Fe Mössbauer spectroscopy in the temperature range of 20–600 K. The ¹¹⁹Sn Mössbauer spectra recorded down to 20 K from the non-iron-containing compounds of Co₃O₄ and Mn₃O₄ contained only doublets showing no transfer of magnetic properties from cobalt or manganese to the dopant tin ions. In contrast, the tin-doped-(FeCo)₃O₄ and (FeMn)₃O₄ gave ¹¹⁹Sn and ⁵⁷Fe Mössbauer spectra, which showed magnetic hyperfine interactions. The Curie temperature has been estimated for the former sample.     

二聚物X2 和 XK (X= Mn, Fe, Co, Ni, Cu)吸附NO的密度泛函理论研究

为有效降低NO对环境以及人体造成的危害,着重从催化剂入手,研究过渡金属Mn₂, Fe₂, Co₂, Ni₂, Cu₂及K掺杂的MnK, FeK, CoK, NiK, CuK的二聚物对NO的吸附性能.采用密度泛函理论的B3LYP, B3PW91, B3P86, B1B95以及PBE1PBE方法结合LANL2DZ, SDD, CEP-121G基组,采用B3LYP, B3PW91, B3P86以及PBE1PBE方法结合6-31++G(3df, 3pd), 6-311++G(3df, 3pd), 6-31G(d, p), LANL2DZ, SDD基组分别系统研究了X₂和XK (X=Mn, Fe, Co, Ni, Cu)团簇和NO的几何结构,计算出其键长,频率,离解能,再与对应的实验值进行对比.进一步采用PBE1PBE方法结合LANL2DZ和6-31G(d, p)基组研究了X₂NO和KXNO团簇的几何结构,计算出各原子间键长和吸附能.结果表明,...