The influence of pressure on spontaneous magnetization of Fe60Mn20B20 amorphous alloy at temperature range 77.4–300 K

Abstract

Amorphous, ferromagnetic, invar like, Fe₆₀ Mn₂₀ B₂₀ alloy has been investigated. Two kinds of experiments were carried out for this alloy. The first, using high pressure technique, revealed the influence of pressure on B(H) dependencies within the wide range of temperature under pressure of 0.5 GPa. From the magnetization curves obtained during these experiments the decrease of spontaneous magnetization caused by applied pressure 0.5 GPa at temperature -180°C has been calculated at the rate about 7 10^?11T/Pa.

In the second kind of experiments the measurements of volume magnetostriction up to 720 kA/m magnetic field intensity have been done. Volume magnetostriction coefficient at temperature 77.4 K has been determined to be about 2 10^?11 [A/m]^?1.     

Electronic and magnetic properties of the iron borate Fe2BO4

Polycrystalline Fe₂BO₄ was prepared by solid state reactions and its electronic and magnetic properties were investigated by Mössbauer spectroscopy and magnetization measurements. The Mössbauer spectra of Fe₂BO₄ below 270 K indicate the presence of Fe²⁺ and Fe³⁺ sites in the structure, in a ratio 1 : 1. Above this temperature electron delocalization sets in between the divalent and trivalent iron ions and Fe^2.5+ states are observed. The temperature dependence of the Mössbauer spectra and magnetization measurements clearly show the onset of magnetic order below 155 K.     

The Influence of the Annealing Temperature on the Properties of Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> Powders Evidenced by EMR Spectroscopy

Electron magnetic resonance (EMR) investigations of Sn_{1− x} Fe _x O₂ (x = 0.07) powders annealed at different temperatures are reported. EMR spectra show the presence of both the isolated paramagnetic Fe³⁺ ions incorporated into the SnO₂ lattice and a ferromagnetically ordered component. By increasing the annealing temperature, the EMR spectrum attributed to the ferromagnetically coupled Fe³⁺ ions diminishes probably due to the migration of Fe ions and the formation of the second phase. The presence of the second phase was evidenced by X-ray diffraction measurements.     

Hyperfine interaction of Ce and La in 3-d ferromagnets

NMR/ON measurements on¹⁴¹CeFe show the sign of the hyperfine field of CeFe to be negative. For the¹⁴¹Ce nucleus a g-factor of ¦g_N¦=0.311±0.011 is found. With this g-value a hyperfine field of H_hf=?41±2 T for CeFe is derived. Low temperature nuclear orientation experiments on¹⁴¹CeCo and¹⁴⁰LaFe yield ¦H_hf¦=30±3 T and ¦H_hf¦=46±5 T respectively. The valence of cerium impurities in Fe, Co and Ni is discussed.     

High-Pressure Mössbauer Measurements on Nanocrystalline Perovskite (La,Sr)(Mn,Fe)O3

We report here the Mössbauer measurements on nanocrystalline perovskite structured manganite La_0.8Sr_0.2Mn_0.8Fe_0.19 ⁵⁷Fe_0.01O₃ as a function of pressure up to 10 GPa at room temperature. The nanocrystalline sample, prepared by sol–gel technique found to have crystallite sizes of ∼138 ± 10 Å. Zero-field electrical resistivity measurements with temperature support the nanocrystalline nature. At ambient pressure, Fe³⁺ as well as Fe⁴⁺ ions are distributed in two different environments – Fe³⁺ in low symmetric site surrounded by Mn³⁺ ions only while Fe⁴⁺ in high symmetric site with at least one Mn³⁺ ion. Pressure seems to affect the higher symmetric site. A sudden increase in isomer shift at 0.52 GPa indicates the first order phase transition representing the transformation of Fe⁴⁺ to Fe³⁺. Another transition at 3.7 GPa, represents the presence of Fe³⁺ in single kind of environment. Pressure dependence of electrical resistivity measurements verifies the transitions attributing the first order transition to the cross over of localized-electron to band magnetism.     

Mössbauer study of CaFeO3 under external high—Pressure

⁵⁷Fe Mössbauer and X-ray diffraction measurements have been performed on a perovskite CaFeO₃ under external high pressure upto 50 GPa at room temperature using a diamond anvil cell. Above 29 GPa the⁵⁷Fe magnetic hyperfine splitting appears superimposing with usual paramagnetic pattern of CaFeO₃. Magnitude of hyperfine field is 16 T and much smaller than 33 T of typical Fe⁴⁺ in SrFeO₃ suggesting a transition from high-spin S=2 to low-spin S=1 state in CaFeO₃.     

Melting and thermal expansion of iron in uniformly laser-heated diamond anvil cells

Abstract

A technique is described to laser heat samples uniformly under hydrostatic pressure conditions to over 2500 K and 400 kbar with very high accuracy in P and T. I re-measured the melting curve of iron by this technique and obtained excellent agreement with my earlier work using resistive wire heating (Boehler 1986). P-V-T measurements on γ-iron to 200 kbar and 2000 K using synchrotron radiation leads to a strong decrease of the thermal expansion coefficient with pressure, (?lnα/?lnV)_T = 6.5. The zero pressure bulk modulus K₀ decreases with temperature by 0.33 kbar deg^?1. This Yields densities of iron at conditions in the Earth's core which are consistent with shock compression measurements. The potiential of studying mineralogical phase transitions by this method is described.     

Magnetic properties of a new BaO.Fe2O3.Na2O glass

Homogeneous BaO.Fe₂O₃.Na₂O glass containing 60% Fe₂O₃ is prepared by splat cooling technique. X-ray diffraction reveals the presence of a few small βNaFeO₂ crystallites in a glassy matrix. DTA studies show that βNaFeO₂ cristallizes first and BaFe₁₂O₁₉ next. In the temperature range 130K < T < 400K this glass shows Curie-Weiss behaviour with large negative Weiss constant. The magnetic susceptibility measurements below 130K exhibit a broad maximum near 90–110K. Mössbauer study reveals that the glass mainly consists of tetrahedral network of Fe³⁺O₄ and a hyperfine structure at low temperature; magnetic ordering temperature estimated is about (125 ± 5)K.     

57Fe,61Ni and91Zr hyperfine field distributions in magnetic Tm-Zr amorphous alloys

Pulsed NMR measurements were performed on [Tm₁ (Tm₂)]_90+x Zr_10?x (Tm=Fe, Co, Ni) amorphous alloys utilizing a newly developed low temperature wide band probehead-preamplifier system. A 11,6 T broad⁵⁷Fe hyperfine field distribution around the average of 23.6 T together with a less intensive peak around 11 T has been found in Fe_90.6Zr_9.4, in excellent agreement with Mössbauer studies. A rather flat distribution around the average value of 14.8 T characterizes the transferred hyperfine field at the Zr sites in the same alloy. Both features provide strong evidence for a broad range of exchange interactions and variations in the spin density at the Fe sites in this material. A much narrower and symmetrical distribution at the Zr sites around 10 T in Co₉₀Zr₁₀ is evidence of the higher magnetic homogeneity of this alloy as compared to Fe₉₀Zr₁₀. In Fe₆₀Ni₃₀Zr₁₀, in addition to the⁵⁷Fe signal, a contribution from⁶¹Ni nuclei could be separated, corresponding to an average hyperfine field value of 15.3 T.     

Indirect measurements of the Jahn-Teller quenched spin-orbit splitting in the 5T2g-state of KMgF3:Fe2+

The energy separation of the first excited spin-orbit States Γ_3g, Γ_4g from the Γ_5g ground state, in the orbital ⁵T_2g triplet state of Fe²⁺ in KMgF₃, has been estimated from temperature dependence measurements on the 7860 cm^-1 zero-phonon-line (ZPL) transition from Γ_5g to the orbital ⁵E_g doublet state. Using a simplified crystal field energy level model, we find the Γ_5g Γ_3g, Γ_4g separation to be ～30 cm^-1, indicating that the vibronic Jahn-Teller coupling is considerably stronger in KMgF₃:Fe²⁺ than in MgO:Fe²⁺. Far infrared absorption data on KMgF₃:Fe²⁺ in magnetic fields up to 6T, are found to be consistent with this interpretation.     

Pulsed fm NMR/on studies of single crystal54MnNi and125SbFe

Precision field shift studies of B_appl-8T using pulsed FM NMR/ON along hard directions (eg <100>⁵⁴MnNi, <112>¹²⁵SbFe and the easy axis (<111>⁵⁴MnNi, <100>¹²⁵SbFe) yield no measurable Knight shifts within the uncertainty allowed by current accuracy of the nuclear moments. This is in striking contrast to earlier measurements with the same apparatus that yielded K=+1.5 (4)% for⁶⁰CoFe. The modulation frequency dependences of the pulsed FMNMR/ON signals are investigated for a variety of rf parameters and compared with model predictions.     

Anisotropy-tuning by doping: phase diagram of CsNi0.98Fe0.02Cl3 measured by caloric experiments

The magnetic phase diagram of the Fe²⁺ doped hexagonal ABX₃ compound CsNi_0.98Fe_0.02Cl₃ is investigated measuring the specific heat capacity and the magnetocaloric effect. In contrast to earlier specific heat, ultrasound and NMR experiments our measurements identify transitions between three ordered phases with the field applied in the hexagonal plane. Since the pure compound, a Heisenberg antiferromagnet with weak Ising anisotropy, has only two ordered phases for this field direction, while three are predicted for weak easy-plane anisotropy, our data provide the unambiguous proof that the anisotropy of CsNiCl₃ can be effectively modeled by doping with Fe²⁺.     

Nuclear orientation study of54Mn impurity in Pt100-x Fe x alloy

The low temperature nuclear orientation of⁵⁴Mn in Pt_99.95Fe_0.05, Pt_99.9Fe_0.1, Pt₉₉Fe₁ and Pt₈₈Fe₁₂ has been studied in the temperature range 12–50 mK and in the external magnetic field range 0–1.2 T. The strong temperature and external magnetic field dependence of the effective fieldB _eff on⁵⁴Mn has been observed even in the range where the host itself is magnetically saturated. This behaviour is interpreted by noncollinearity of the Mn magnetic moments with respect to the macroscopic magnetisation direction.     

DPAC measurement of the hyperfine fields in100RhCo and100RhFe

Using the 85–75 keV -cascade of¹⁰⁰Rh, we report the first DPAC measurement of the hyperfine field in¹⁰⁰RhCo and¹⁰⁰RhFe. Our results were made possible by continued improvement in time resolution using BaF₂ scintillators. At room temperature we obtained fields of 420.6(1.3) kG and 540.4(1.5) kG for¹⁰⁰RhCo and¹⁰⁰RhFe, respectively. The former revises an earlier spin echo result by Kontani and Itoh by 9%; the latter is consistent with the work of Matthiaset al. using resonant destruction of angular correlations.     

Corelationship between local structure and water purifying ability of iron-containing waste glasses

A relationship between the structure and water purifying ability of waste glass prepared from household garbage and Fe₂O₃ was examined by ⁵⁷Fe-Mössbauer and induced coupled plasma (ICP) measurements. From the Debye temperature of waste glass, Fe^II proved to be loosely bound in the glass network as a network modifier. Dissolution amount of Fe^III into artificial drain can be controlled from 0.14 to 0.35 mg/l by changing the Fe₂O₃ content. It proved that chemical oxygen demand (COD) decreases in proportion to the content of Fe^III, indicating that iron causes decomposition of organic and phosphorus compounds.     

Magnetic behaviour of the mixed spinel ferrite GaxFe1-xNiCrO4

Mössbauer, X-ray diffraction, dc magnetization and ac susceptibility measurements have been carried out in the spinel ferrite Ga_xFe_1-xNiCrO₄ (0⩽x⩽1) in different temperature ranges between 1.4 and 700 K. These measurements show A site occupation of Fe³⁺ ions and a coexistence of ferrimagnetic and frustrated (entropic) spins in this system for all x. The frustration in this system arises due to the random distribution of Fe³⁺ and diamagnetic Ga³⁺ ions on the A sites, and those of Ni²⁺ and Cr³⁺ ions on B sites.     

Satellite line structure in NMR-ON on206BiFe and182ReFe

Nuclear magnetic resonance on oriented²⁰⁶BiFe and¹⁸²ReFe has been measured using recoil implanted samples. Clearly resolved satellite structures were found for both systems. By annealing at an appropriate temperature, the resonance width was reduced. The satellite line structure for¹⁸²ReFe was studied with various annealing temperatures. The ratio of the resonance strength changed with the annealing temperature. The resonances for¹⁸²ReFe were also measured in external magnetic fields of 0.1, 0.2 and 0.4 T. The resonance frequencies for the satellite structure at an external magnetic field of 0.2 T were determined:v ₁=691.7(3),v ₂=684.4(2),v ₃=687.2(2) MHz for²⁰⁶BiFe;v ₁=231.15(5),v ₂=230.20(5) for¹⁸²ReFe. The origin of the satellite structure is discussed. The effective relaxation time of¹⁸²ReFe at 8 mK and external magnetic field of 0.2 T was determined to be 18.6(6) s using a single-exponential fit.     

Fe掺杂对自旋梯状化合物Sr14(Cu1－yFey)24O41的结构和电输运性质的影响

采用常规的固相合成法分别制备了Fe³⁺掺杂和2/3Fe³⁺+1/3Fe²⁺混合Fe离子掺杂的两组Sr₁₄(Cu_1-yFe_y)₂₄O₄₁系列样品.X射线衍射分析显示，当Fe³⁺离子的掺杂量y≤0.03以及2/3Fe³⁺+1/3Fe²⁺混合Fe离子掺杂量y≤0.02时，样 关键词： 强关联电子系统 自旋梯状结构化合物 晶体结构 电输运性质     

The interplay between the lattice and magnetism in La（Fe11.4Al1.6）C0.02 studied by powder neutron diffraction

The crystallographic structure and magnetic properties of La（Fell.4Alz.6）C0.02 are studied by magnetic measurernent and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La（Fe11.4Al1.6）C0.02 crystallizes into the cubic NaZn13-type with two different Fe sites： FeI （8b） and FeII （96i）, and that A1 atoms preferentially occupy the FeII site. A ferromagnetic state can he induced at a medial temperature of 39 K-139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La（Fe11.4Al1.6）C0.02 has no net magnetization in the paramagnetic （T 〉 TN = 182 K） or antifer- romagnetic states, and thus keeps its small lattice. Analysis of the Fe Fe bond length indicates that the ferromagnetic state prefers longer Fe-Fe distances.     

Effective magnetic fields on Fe in R1+εFe4B4 alloys

⁵⁷Fe Mössbauer spectra of magnetically ordered R_1+εFe₄B₄ alloys have been measured at low temperatures. Small (⋍ 0.8 T) hyperfine fields have been found for R = Sm and Dy. Analysis of the spectra in terms of simultaneous magnetic and quadrupolar interactions has revealed the magnetization to be parallel to the c axis for R = Sm and perpendicular to the c axis for R = Dy. These results are consistent with a 2^nd-order CEF mechanism for anisotropy. The ordering temperature of Sm_1+εFe₄B₄ was determined from Mössbauer and magnetization measurements to be T_c = 37 ± 2 K, the highest in the R_1+εFe₄B₄ series.