High-temperature heat capacity of BaFe12O19 and BaSc0.5Fe11.5O19

Physics of the Solid State - Data on the heat capacity of BaFe12O19 (373–1450 K) and BaSc0.5Fe11.5O19 (408–1000 K) have been obtained. In the temperature dependences of the heat...     

The dynamics of iron ions in pseudotetrahedral (bipiramidal) sites of BaFe12O19 and SrFe12O19 hexagonal ferrites

A comparative Mösbbauer study of the dynamics of iron in pseudotetrahedral (bipiramidal) 4e sites has been performed on BaFe₁₂O₁₉ and SrFe₁₂O₁₉ single crystals from 4.2 to 295 K. The measured angular and temperature dependence of the recoil-free fraction evidenced the influence of the heavy divalent cations on the dynamics of iron in 4e sites.     

Resonance features of the dynamic magnetic susceptibility in hexaferrite BaFe12O19 upon the transition from the magnetically ordered state to the paramagnetic state

This paper presents the results of the experimental study on the dynamic magnetic susceptibility of barium hexaferrite crystals in the temperature range of the transition from the magnetically ordered state to the paramagnetic state. The observed features of the magnetic susceptibility have been interpreted as those characteristic of the ultralow-frequency natural ferromagnetic resonance of the spin subsystem of the Bloch domain walls. The results agree well with the concepts of features of the critical spin dynamics near the Curie temperature.     

Nonequivalent positions of Fe3+ ions and relaxation effects in Mn-Zn-ferrites

A study is made of manganese-zinc ferrites Mn_1–xZn_xFe₂O₄ where x varies from 0.3–0.9. It is established that the variation of the form of the spectra with variation of x is of a relaxation nature. In this system the nonequivalent nature of the neighborhood of the ions has an effect on the relaxation processes and on the character of the magnetic ordering.Translated from Izvestiya VUZ, Fizika, No. 3, pp. 77–81, March, 1973.     

Determination of directions of internal fields in BaFe12O19

Mössbauer-absorption measurements were carried out on single crystals and polycrystalline samples of BaFe₁₂O₁₉ (BaM). This material has an easy axis of magnetization along the c axis. At the iron 12k site a deviation of the directions of the internal fields from the c axis is shown. Both the EFG's and the magnetic dipole fields at the iron 12k site form an ‘umbrella’ around the c axis.     

Iron ions in ZSM-5 zeolite: Fe3+ in framework, Fe2+ in extra-framework positions in catalytic N2O decomposition

Fe-ZSM-5 samples containing a combination of ⁵⁷Fe³⁺ in framework (FW) and regular iron in extra-framework (EFW) sites were prepared by introducing ⁵⁷Fe in hydrothermal synthesis, then exchanging Fe²⁺ of natural isotope composition into the lattice. The stability for one part of Fe²⁺ and Fe²⁺ ? Fe³⁺ reversibility for the other part in catalytic decomposition of N₂O is demonstrated by in situ Mössbaer measurements. Formation of dinuclear Fe_FW–O–Fe_EFW pairs is not prevailing.     

Effect of diamagnetic substitutions in BaFe12O19 on the magnetic properties

The exchange parameters of BaFe₁₂O₁₉ have been calculated from the temperature dependence of the saturation magnetization using the molecular field theory. Under the assumption that the exchange parameters do not change for diamagnetic substitutions of the Fe³⁺ ions, it is shown that the temperature coefficient of the magnetization at room temperature cannot be decreased without decreasing the magnetization. Diamagnetic substitution in the octahedralf ₂ site would solely increase the saturation magnetization.     

二元比例X射线荧光光谱法测定BaFe12O19中Fe和Ba的含量

采用二元比例X射线荧光光谱法测定铁钡氧体BaFe12O19中铁(Fe)和钡(Ba)的含量,为铁钡氧体BaFe12O19的定量分析建立了一种新的分析方法.选取纯Fe粉(分析纯)及纯BaCO3粉(分析纯),采用粉末压片法自制标准样品,建立了定标曲线.选用Fe含量为75％、Ba含量为17.4％的标准样品作为验证样品,对定标曲线的准确度进行验证.经分析得到验证样品中Fe和Ba含量分别为75.68％和16.92％,相对标准偏差分别为0.317％和1.11％,可知定标曲线具有良好的线性关系,且准确度高,精密度好.实验测得BaFe12O19样品中Fe和Ba的含量分别为57.28％和13.42％,相对标准偏差为1.05％和0.73％.     

Domain Structure of Hexaferrite BaFe12O19 Near the Curie Temperature

Physics of the Solid State - The features of the structure of domain walls in hexaferrite BaFe12O19 have been studied near the Curie temperature TC = 724 K. The studies have been performed on the...     

Room temperature multiferroism and magnetoelectric coupling in BaTiO3–BaFe12O19 system

A new multiferroic system comprising of BaTiO₃ (BT) and BaFe₁₂O₁₉ (BF) have been synthesized and investigated. The presence of both phases i.e., Piezoelectric/Ferroelectric and Piezomagnetic/Ferrimagnetic phases was confirmed by X-ray diffraction studies. With the decrease of Ferrite content, the ferroelectric polarization values have increased and hysteresis loops were recorded. The ferrimagnetic nature was dominant in all the ferrite compositions with a high coercivity of 3.5 kOe. Magnetoelectric hysteresis loops were recorded from the room temperature magnetoelectric (ME) measurements and the output has shown non-linearity indicating striction induced phenomena in BT–BF system.     

Magnetic anisotropy manipulation and interfacial coupling in Sm3Fe5O12 films and CoFe/Sm3Fe5O12 heterostructures

The magnetic anisotropy manipulation in the Sm₃Fe₅O₁₂ (SmIG) films and its effect on the interfacial spin coupling in the CoFe/SmIG heterostructures were studied carefully. By switching the orientation of the Gd₃Ga₅O₁₂ substrates from (111) to (001), the magnetic anisotropy of obtained SmIG films shifts from in-plane to out-of-plane. Similar results can also be obtained in the films on Gd₃Sc₂Ga₃O₁₂ substrates, which identifies the universality of such orientation-induced magnetic anisotropy switching. Additionally, the interfacial spin coupling and magnetic anisotropy switching effect on the spin wave in CoFe/SmIG magnetic heterojunctions have also been explored by utilizing the time-resolved magneto-optical Kerr effect technique. It is intriguing to find that both the frequency and effective damping factor of spin precession in CoFe/SmIG heterojunctions can be manipulated by the magnetic anisotropy switching of SmIG films. These findings not only provide a route for the perpendicular magnetic anisotropy acquisition but also give a further path for spin manipulation in magnetic films and heterojunctions.     

Mössbauer measurements of the bipyramidal lattice site in BaFe12O19

Mössbauer measurements have been made on polycrystalline barium ferrite samples. The subspectrum corresponding to the iron ion in the bipyramidal lattice site in the temperature range from T = 4.2K up to T = 870K was obtained. Based on the temperature dependence of the unusually large quadrupole splitting due to ferric iron in the bipyramidal position, a model of this lattice site is proposed in which the iron ion is located at one of two equivalent positions of Wyckhoff notation 4e, separated by a potential barrier. At sufficiently high temperature the ion jumps between the two 4e sites with a jump frequency which is greater than the inverse of the lifetime of the 14.4 keV state of ⁵⁷Fe. This is in agreement with Mössbauer measurements, molecular-orbital studies and previous X-ray data.     

Raman scattering studies of spin‐waves in hexagonal BaFe12O19

We present the results of polarized Raman spectroscopy of hexagonal BaFe₁₂O₁₉ single crystal. The spectra, recorded from 200 to 800 cm^–1 and 1100 to 1700 cm^–1 in the 20–250 K temperature range, are analyzed on the basis of both crystal vibrations and spin‐waves. In the low wavenumber range, the Γ‐point phonons are observed. In the high wavenumber range, phonon mixings are observed; more interestingly, four modes of spin‐waves are identified in hexagonal BaFe₁₂O₁₉. Both have not been studied previously. Our analyses of the spin‐waves provide an optical method for quantitatively estimating the spin exchange interactions in hexagonal BaFe₁₂O₁₉. The four strong exchange integrals are found to have the values of J_ce = 1.31 meV, J_ae = 1.36 meV, J_cd = 1.46 meV, and J_bd = 1.71 meV. Our results also indicate that at ~200 and ~80 K, there would be additional spin‐ordering transitions in hexagonal BaFe₁₂O₁₉. Copyright © 2012 John Wiley & Sons, Ltd.     

Atomic absorption background of Ba in EXAFS analysis of BaFe12O19 nanoparticles

The approximate barium X‐ray atomic absorption in the energy region of L‐edges is reconstructed from the absorption spectrum of an aqueous solution of BaCl₂. The result is corroborated by comparison with pure atomic absorption spectra of neighbour elements Xe and Cs. The application of the atomic absorption signal as a proper EXAFS background is demonstrated and discussed in the analysis of Ba hexaferrite nanoparticles with a very weak structural signal. The essential gain is found in the decrease of uncertainty intervals of structural parameters and their correlations. A simple analytical model of the absorption background for the practical EXAFS analysis is demonstrated.     

SrAl12O19∶Pr3+中的热激发

研究了SrAl12O19∶Pr3+的光谱中3P1 和1I6的发射. 用3P1→3H5与3P0→3H5发射强度之比测量了温度，通过1I6→1G4与3P0→1G4发射强度之比，讨论了热激发对3P0可见光发射效率的影响. 关键词： 热激发 温度测量 三价镨离子     

Surface of the BaFe12O19 crystal and its influence on the interparticle magnetic interaction

Physics of the Solid State - The influence of the physicochemical state of the particle surface on the interparticle magnetic interaction in a close-packed system of single-domain microcrystals of...     

Mössbauer study of BaFe12O19 fine particles prepared by the glass-ceramic method

BaFe₁₂O₁₉ fine particles were prepared by the glass-ceramic method with the BaCO₃?B₂O₃?Fe₂O₃ glass system. The effect of technology factors on the Mössbauer spectra and Hc was investigated. The possible mechanism of magnetization reversal of the BaM fine particles was discussed.