Hyperfine fields and magnetic transitions in the low iron concentration range of the crystalline FexNi75−xP25-alloys

The crystalline system Fe_xNi_75−xP₂₅ was studied in the low iron concentration range by ⁵⁷Fe Mössbauer spectroscopy and dc-magnetization measurements. From the latter method the magnetic phases were determined to be spin-glass like but on a more local scale, from ⁵⁷Fe Mössbauer spectroscopy, it was found that the magnetic phases were rather inhomogeneous, therefore leading to not sharp phase transitions in the investigated samples.     

Magnetic behavior of 3d dopants in superconducting REBa2Cu3−xFexO7+δ (RE=Dy, Er)

Mössbauer studies on ⁵⁷Fe-doped superconducting REBa₂Cu₃O_7+δ (RE=Er, Dy) were made as a function of temperature for x=0.15 and 0.30. The magnetic behavior of the 3d dopants, which mainly occupy Cu(1) sites, undergoes antiferromagnetic ordering which is coexistent with superconductivity at low temperature. The dimensionality of the magnetic interaction changes from 2D to 3D when the rare earth changes from Er to Dy. the line-widths of the Mössbauer subspectra are characteristic of magnetic fluctuation behavior in the vicinity of a phase transition. Combining these results with those of Fe-doped Y-123 (pseudo 1D) and Gd (3D), the magnitude of the rare earth moments appears to be strongly correlated with the dimensionality of the magnetic interaction of Fe dopants in these compounds. However, the Mössbauer spectrum for ¹⁵⁵Gd in GdBa₂Cu_2.85Fe_0.15O_7+δ (T_{N(Fe) 14 K}) shows no magnetic order at 4.9 K.     

Mössbauer studies of CoxFe1−xCr2S4

The mixed spinel systems Co_xFe_1−xCr₂S₄ has been studied using the Mössbauer effect. Spectra have been collected over the temperature range 83–300 K. The isomer shifts indicate that the charge states of Fe ions are ferrous in character throughout the series. Absence of quadrupole splitting above the magnetic ordering temperature T_c suggests that iron ions occupy only tetrahedral sites. It is notable that as the temperature decreases below T_c, both quadrupole shift and asymmetrical line-broadening appear and increase with decreasing temperature, suggesting the presence of electric field gradient and accompanying relaxation effects.     

Estimation of the exchange constants in the Fe sublattice of the Y2Fe17 and Y2Fe17N3−δ compounds from the analysis of Mössbauer measurements

From the analysis of Mössbauer data for Y₂Fe₁₇ and Y₂Fe₁₇N_3−δ at various temperatures the hyperfine fields for 4f, 6g, 12j, 12k iron sites were estimated as a function of temperature. The reduced magnetizations calculated from the values of the hyperfine fields are fitted with a mean field model for four interacting sublattices using a computer program. The estimated exchange interaction from the fitting procedure between the 4f sites is found strongly negative (antiferromagnetic) in Y₂Fe₁₇ whereas in Y₂Fe₁₇N_3−δ it increases and becomes weak negative following a modified Slater-Néel curve. The rest of the exchange interactions are found positive or weak negative depending on the distances between the Fe atoms.     

Localized canting of spins structure in the spinel oxide system: ZnzTizFe2−x−zCrx−zCoO4

The spinel oxide system Zn_zTi_zFe_2−x−zCr_x−zCoO₄; z=x²; x=0.60, 0.65, 0.70 and 0.80, was studied using neutron diffraction technique, low field DC magnetization measurements (ZFC–FC measurements), magnetic hysterisis, Mössbauer spectroscopy and low field AC susceptibility measurements. All the compositions show significantly less B-site magnetic moments at 10 K temperature derived from neutron diffraction data than the free ions site moments deduced assuming collinear arrangement of spins. This combined with some other features seen in the low temperature neutron diffraction patterns suggest localized canting of spins (LCS) type of magnetic ordering in the present system where a long range order of longitudinal component of moments co-exists along with totally disordered transverse component of moments. The conclusion is also supported by the features seen in the other measurements. The magnetic moments derived from 10 K neutron diffraction data are explained using the LCS approach for different exchange integrals ratios.     

High field Mössbauer investigations of paramagnetic Y(Fe, Al)2

⁵⁷Fe Mössbauer measurements in external fields up to 13.5 T in the temperature range 4–300 K are reported for Y(Fe_xAl_1−x)₂. A negative sign was found for the quadrupole splitting. In the paramagnetic state different induced hyperfine fields for different Fe environments were observed.     

Magnetic phase transition between ferromagnetic and antiferromagnetic states in Ce(Fe1−xAlx)2

The cubic Laves phase compound Ce(Fe_0.95Al_0.05)₂ exhibits a first order magnetic phase transition from antiferromagnetic to ferromagnetic state at ≈ 100 K with increasing temperature. This note gives the results of the Mössbauer effect of ⁵⁷Fe and the magnetic phase diagram in the external field vs. temperature plane.     

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.     

Magnetic moments and Fe hyperfine field interactions in Y(Fe1−xRux)2 ternaries

Measurements of magnetization and ⁵⁷Fe Mössbauer spectra have been made for Y(Fe_1−xRu_x)₂. The C15 type cubic structure is stabilized for xx 0.7. The C15 compounds is ferromagnetic with T_c200 K and its saturation moment decreases monotonically with increasing x, while the ⁵⁷Fe hyperfine field decreases only slightly with x. From these results, it is deduced that the Ru atoms have an induced moment of ≈1μ_B in the range x 0.2. In the C14 type phase, no magnetic ordering develops even at 4.2 K.     

Itinerant magnetism in TiMxBe2-x (M = Cu, Fe)

Magnetization and Mössbauer studies of TiCu_xFe_yBe_2-x-y (x = 0, 0.03, 0.4, y = 0, 0.02) show that TiBe₂ is an enhanced paramagnet, 0.02 Fe or 0.03 Cu reduce the susceptibility. On the other hand, TiCu_0.4Be_1.6 is ferromagnetic (T_c = 20 K) and 0.02 Fe reduces the magnetization and Curie point (T_c = 16 K). The magnetic properties of all samples are extremely sensitive to sample preparation and heat treatments.

The Mössbauer studies show that the itinerant magnetism resides on the Ti site, all Ti sites have the same local spin density irrespective of local environment.     

Crystallization kinetics of the Fe40Ni38Mo4B18 amorphous alloy

X-ray diffraction (XRD) and Mössbauer spectroscopy were used to study the annealing of the Fe₄₀Ni₃₈Mo₄B₁₈ amorphous alloy. The samples were isothermally annealed in the 858–878 K temperature range several times. Two crystalline phases were observed in the annealed samples: FeNi₃ and (Fe, Ni, Mo)₂₃B₆. Preliminary results indicate that assuming a linear relationship between the area under the main XRD peak associated with the FeNi₃ phase and its volume fraction, this can be fitted to a Johnson–Mehl–Avrami equation with an exponent n close to 1.0. Mössbauer results show a broad magnetic hyperfine field distribution in as-received samples and, consistent with XRD results, a sextet attributed to precipitates of FeNi₃ (B_hf=29.5 T) for long annealing times.     

Effects of structure on exchange interactions in crystalline and amorphous alloys GdxY50−xAg50

Magnetic interactions and effects of dilution with nonmagnetic Y on the magnetic properties of crystalline and amorphous alloys Gd_xY_50−xAg₅₀ (10 ≤ x ≤ 50) have been investigated by measurements of bulk magnetization and susceptibility and by Mössbauer spectroscopy with ¹⁵⁵Gd. The crystalline alloys order antiferromagnetically for all Gd concentrations with a noncollinear arrangement of Gd moments induced by negative biquadratic exchange interactions. In amorphous alloys, ferromagnetic order is found for large Gd concentrations (x ≥ 40). Below the critical concentration x_cr, in the range 30<x_cr<40, properties typical for magnetic cluster glasses are observed. Magnetic hyperfine fields B_hf at ¹⁵⁵Gd nuclei vary with x in opposite directions in amorphous and in crystalline alloys. In crystalline alloys, the variation is due to a positive transferred hyperfine field. In amorphous alloys, a reduction of |B_hf| with decreasing Gd concentration is caused by a reduction of the frozen Gd moments in the cluster glass phase.     

阎隙碳原子对Er2Fe17Cx化合物结构与磁性的影响

利用快淬手段获得高碳含量的Er₂Fe₁₇C_x单相化合物,系统研究了Er₂Fe₁₇C_x(x=0.0,0.5,1.0,1.5,2.0,2.5,2.8和3.0)的结构、相稳定性及内禀磁性,讨论了间隙碳原子对化合物中原子磁矩、交换作用和各向异性的影响,同时用⁵⁷Fe穆斯堡尔效应分析了化合物中各个铁晶位的超精细场随碳含量的变化。 关键词：     

Study of the magnetism and the magnetic anisotropy of Fe layers in Ni/Fe/Ni(1 1 1) by Mössbauer spectroscopy

The hyperfine field and the magnetic anisotropy of a Fe layer as a function of thickness have been investigated in several Ni/⁵⁷Fe_x/Ni(1 1 1) trilayers with relatively thick Ni layers by Mössbauer spectroscopy. For Fe layers with thickness below 16 Å, the Mössbauer spectra show always the presence of two ferromagnetic phases with high-spin state. In the range between 6 and 8 Å, also a ferromagnetic phase with low-spin state and a paramagnetic phase have been found. The evolution of the mean hyperfine field of the ⁵⁷Fe nuclei is used to study the Fe growth. A structural FCCBCC phase transition is found to begin with an iron thickness of 8 Å. The easy direction of the magnetization is found out-of-plane for Fe interlayer with FCC structure, and perfectly in plane for Fe interlayer with BCC structure.     

在永磁体强磁场中Mn1.2Fe0.8P1-xSix系列化合物热磁发电研究

研究了处于永磁体强磁场中Mn_1.2Fe_0.8P_1-xSi_x 系列化合物的热磁发电性能, 采用高性能球磨和固相烧结合成方法制备了Mn_1.2Fe_0.8P_1-xSi_x 系列化合物, 并对该系列化合物的物相结构、磁性和热磁发电性能进行了测量. 结果表明: Mn_1.2Fe_0.8P_0.37Si_0.63和Mn_1.2Fe_0.8P_0.35Si_0.65化合物是具有Fe₂P型六角结构的一级相变软磁性材料, 两者居里温度分别为334 K和348 K, 处于工业余热温区. 根据一级相变磁性材料在居里温度磁化强度发生突变这一特性, 研制热磁发电演示装置, 测量了Mn_1.2Fe_0.8P_0.37Si_0.63和Mn_1.2Fe_0.8P_0.35Si_0.65这两种材料铁磁相变产生感应电流大小与线圈匝数、热磁发电材料质量、表面积、表面上温度梯度的关系. 研究结果表明, Mn_1.2Fe_0.8P_1-xSi_x系列化合物具有很好的热磁发电性能, 有望成为热磁发电候选材料.     

The BCC to FCC/HCP phase transformation of the Co70Fe30 alloy produced by ion irradiation of Co70Fe30/Cu discontinuous multilayers

We report on the BCC to FCC/HCP structural transformation of Co₇₀Fe₃₀ alloy produced by room temperature ion irradiation of Co₇₀Fe₃₀/Cu discontinuous multilayers. The structural changes were analyzed by X-ray diffraction and X-ray absorption spectroscopy. For this study, two different samples were examined, one irradiated with 50 keV He⁺ and another with 600 keV Kr⁺ with doses of 1×10¹⁷ and 3×10¹⁵ ions/cm², respectively. No substantial change is observed after He⁺ irradiation, while after Kr⁺ irradiation an unexpected structural transition from BCC to FCC/HCP closed packed of the Co₇₀Fe₃₀ alloy was found.     

包钴铁氧体型γ-Fe2O3磁粉穆斯堡尔效应的研究

包钴铁氧体型,γ-Fe₂O₃磁粉(简记为CoFe-γ-Fe₂O₃)是针状γ-Fe₂O₃磁粉与Co⁺⁺和Fe⁺⁺溶液起反应,在每个针状颗粒上包覆了一层钴铁氧体固溶体。经此种方法处理后的γ-Fe₂O₃磁粉的矫顽力及其它磁特性有较大的提高。如矫顽力由原来415Oe增加到715Oe;剩磁和矫顽力随时间及温度变化小等。我们利用穆斯堡尔效应并配合其它研究手段进行了研究,认为:CoFe-γ-Fe₂O₃磁粉矫顽力的提高,主要是由于γ-Fe₂O₃磁粉表面包覆了一层钴铁氧体固溶体,γ-Fe₂O₃与钴铁氧体固溶体之间发生磁耦合作用之故。 关键词：     

Mössbauer-effect studies of multilayers and interfaces

The usefulness of Mössbauer spectroscopy for the investigation of magnetic multilayer systems is described. By applying ⁵⁷Fe Mössbauer spectroscopy, the behavior of ultrathin magnetic layers, such as FCC-like Fe films on Cu(0 0 1), is studied. Position-specified (depth-selective) information is available by preparing samples in which monatomic ⁵⁷Fe probe layers are placed at specific vertical positions, e.g. at interfaces or at the surface. As demonstrated for epitaxial chemically ordered Fe₅₀Pt₅₀ alloy films and polycrystalline nanostructured Tb/Fe multilayers, the Fe-spin structure can be determined directly, and a site-selective Fe-specific magnetic hysteresis loop can be traced in very-high-coercivity materials. For the studies of non-magnetic layers, on the other hand, hyperfine field observations by ¹⁹⁷Au and ¹¹⁹Sn probes are worthwhile. Spin polarizations in Au layers penetrating from neighboring ferromagnetic 3D layers are estimated ¹⁹⁷Au from Mössbauer spectra and are also studied by inserted ¹¹⁹Sn probes in Au/3D multilayers. In the Sn spectra for Cr/Sn multilayers, it was found that remarkably large spin polarization is penetrating into Sn layers from a contacting Cr layer, which suggests that Cr atoms in the surface layer have a ferromagnetic alignment.     

Magnetostriction and spin reorientation in ferromagnetic Laves phase Pr(Ga_xFe_(1-x))_(1.9) compounds

The magnetostriction, magnetization, and spin reorientation properties in Pr(Ga_xFe_(1-x))_(1.9) alloys have been investigated by high-precision x-ray diffraction(XRD) step scanning, magnetization, and Mo¨ssbauer spectra measurements. Ga substitution reduces the magnetostriction(λ_(||)) with magnetic field H ≥ 8 kOe(1 Oe = 1.33322×10~2 Pa), but it also increases the λ|| value when H ≤ 8 kOe at 5 K. Spin-reorientations(SR) are observed in all the alloys investigated, as determined by the step scanned XRD, Mo¨ssbauer spectra, and the abnormal temperature dependence of magnetization. An increase of the spin reorientation temperature(T_(SR)) due to Ga substitution is found in the phase diagram, which is different from the decrease one in many R(T_x Fe_(1-x))_(1.9)(T = Co, Al, Mn) alloys. The present work provides a method to control the easy magnetization direction(EMD) or T_(SR) for developing an anisotropic compensation system.     

Hyperfine investigations of the magnetic state in ordered Pt3−xFe1+x

Mössbauer effect studies of Pt_3−xFe_1+x fcc ordered alloys in the range 4.2 K <T<300 K, in zero and in external magnetic field, for samples with x = 0.16 to 0.28, are reported. The low-temperature spectra show several satellite lines which are related to different excess-Fe nearest-neighbor configurations. Experiments in external fields give information on the different local spin structure at different concentrations.