scholarly journals Lamellar magnetism and exchange bias in billion-year-old metamorphic titanohematite with nanoscale ilmenite exsolution lamellae: III. Atomic-magnetic basis for experimental results

2021 ◽  
Author(s):  
Peter Robinson ◽  
S A McEnroe ◽  
R J Harrison ◽  
K Fabian ◽  
F Heidelbach ◽  
...  
Keyword(s):  
Low Temperature ◽  
Exchange Bias ◽  
Remanent Magnetization ◽  
Domain Walls ◽  
Magnetic Moments ◽  
Magnetic Domain ◽  
Preferred Orientation ◽  
Zero Field ◽  
Lattice Preferred Orientation ◽  
Simple Models

Summary Lamellar magnetism is a source of remanent magnetization in natural rocks different from common bulk magnetic moments in ferrimagnetic minerals. It has been found to be a source for a wide class of magnetic anomalies with extremely high Koenigsberger ratio. Its physical origin are uncompensated interface moments in contact layers of nanoscale ilmenite lamellae inside an hematite host, which also generate unusual low-temperature (low-T) magnetic properties, such as shifted low-T hysteresis loops due to exchange bias. The atomic-magnetic basis for the exchange bias discovered in the hematite-ilmenite system is explored in a series of articles. In this third article of the series, simple models are developed for lamellae interactions of different structures when samples are either cooled in zero-field, or field-cooled in 5 T to temperatures below the ordering temperature of ilmenite. These models are built on the low-temperature measurements described earlier in Paper II. The important observations include: a) the effects of lamellar shapes on magnetic coupling, b) the high-T acquisition of lamellar magnetism and low-T acquisition of magnetization of ilmenite lamellae, c) the intensity of lamellar magnetism and the consequent ilmenite magnetism in populations of randomly oriented crystals, d) lattice-preferred orientation of the titanohematite host crystal populations, and e) the effects of magnetic domain walls in the host on hysteresis properties. Based on exemplary growth models of lamellae with different geometries and surface couplings we here provide simple models to assess and explain the different observations listed above. Already the simplified models show that the shapes of the edges of ilmenite lamellae against their hematite hosts can control the degree of low-T coupling between ilmenite, and the lamellar magnetic moments. The models also explain certain features of the low-T exchange bias in the natural samples and emphasize the role of lattice-preferred orientation upon the intensity of remanent magnetization. The inverse link between ilmenite remanence and exchange-bias shift in bimodal low-T ilmenite lamellae is related to different densities of hematite domain walls induced by the clusters of ilmenite lamellae.

scholarly journals Magnetic characterization of cobalt nanowires and square nanorings fabricated by focused electron beam induced deposition

2018 ◽  
Vol 9 ◽  
pp. 1040-1049 ◽  
Author(s):  
Federico Venturi ◽  
Gian Carlo Gazzadi ◽  
Amir H Tavabi ◽  
Alberto Rota ◽  
Rafal E Dunin-Borkowski ◽  
...  
Keyword(s):  
Electron Beam ◽  
Domain Walls ◽  
Magnetic Moments ◽  
Magnetic Domain ◽  
Hysteresis Loops ◽  
Electron Holography ◽  
Magnetic Dipoles ◽  
Plane Field ◽  
Magnetic Domain Walls ◽  
Electron Beam Induced Deposition

The magnetic properties of nanowires (NWs) and square nanorings, which were deposited by focused electron beam induced deposition (FEBID) of a Co carbonyl precursor, are studied using off-axis electron holography (EH), Lorentz transmission electron microscopy (L-TEM) and magnetic force microscopy (MFM). EH shows that NWs deposited using beam energies of 5 and 15 keV have the characteristics of magnetic dipoles, with larger magnetic moments observed for NWs deposited at lower energy. L-TEM is used to image magnetic domain walls in NWs and nanorings and their motion as a function of applied magnetic field. The NWs are found to have almost square hysteresis loops, with coercivities of ca. 10 mT. The nanorings show two different magnetization states: for low values of the applied in-plane field (0.02 T) a horseshoe state is observed using L-TEM, while for higher values of the applied in-plane field (0.3 T) an onion state is observed at remanence using L-TEM and MFM. Our results confirm the suitability of FEBID for nanofabrication of magnetic structures and demonstrate the versatility of TEM techniques for the study and manipulation of magnetic domain walls in nanostructures.

scholarly journals Особенности релаксации остаточной намагниченности антиферромагнитных наночастиц на примере ферригидрита

2020 ◽  
Vol 62 (7) ◽  
pp. 1043
Author(s):  
Д.А. Балаев ◽  
А.А. Красиков ◽  
А.Д. Балаев ◽  
С.В. Столяр ◽  
В.П. Ладыгина ◽  
...  
Keyword(s):  
Exchange Bias ◽  
Exchange Coupling ◽  
Remanent Magnetization ◽  
Zero Field ◽  
Bias Effect ◽  
Exchange Bias Effect ◽  
Magnetization Relaxation ◽  
Potential Barriers ◽  
Zero Field Cooling ◽  
Field Cooling

In this work, we studied the relaxation of the remanent magnetization of antiferromagnetically ordered ferrihydrite nanoparticles under the conditions of realization of the exchange bias effect for these systems. Magnetization relaxation is characterized by a logarithmic dependence on time, which is typical for thermo-activation processes of the hopping of the magnetic moment of particles through potential barriers caused by magnetic anisotropy. The energy of the barriers obtained from processing the data on relaxation of the remanent magnetization (under the conditions of field cooling) significantly exceeds that for ordinary conditions (zero field cooling). The observed difference indicates the possibility of using the residual magnetization relaxation process to analyze the mechanisms responsible for the effect of exchange bias in antiferromagnetic nanoparticles and obtain the parameters characterizing the exchange coupling of magnetic subsystems in such objects.

scholarly journals EFFECTS OF LOW-TEMPERATURE TREATMENT ON MAGNETIC PROPERTIES OF SM(CO,CU,FE) COMPOUNDS

2020 ◽  
pp. 149-161
Author(s):  
Елена Михайловна Семенова ◽  
Марина Борисовна Ляхова ◽  
Дмитрий Викторович Иванов ◽  
Юлия Васильевна Кузнецова ◽  
Дмитрий Юрьевич Карпенков ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Fractal Dimension ◽  
Low Temperature ◽  
Coercive Field ◽  
Remanent Magnetization ◽  
Magnetic Domain ◽  
Temperature Treatment ◽  
Homogeneous Microstructure ◽  
Low Temperature Treatment ◽  
Temperature Heat

Представлены результаты исследования микро-, нано- и магнитной доменной структуры сплавов Sm(CoCuFe) после выплавки и термических обработок. Показано, что гомогенизация и последующий низкотемпературный отжиг при 400 °С позволяют сформировать микроскопически гомогенную структуру с наноразмерными неоднородностями по составу. Такая структура позволяет реализовать в образцах коэрцитивную силу H до 32 кЭ на литых образцах. Температурные зависимости коэрцитивной силы и остаточной намагниченности образцов в диапазоне от 300 до 700 К имеют линейно убывающий характер. Показано, что наноструктуре сплава с наибольшей H соответствует фрактальная размерность D- ~ 2,3. The results on the micro- and nanostructures and on the magnetic domain structure of Sm(CoCuFe) compound are presented. It was shown that the sequential high- and low-temperature heat treatments lead to formation of a homogeneous microstructure with some nanoscale compositional heterogeneities. Such a structure provides the coercive field H of up to 32 kOe. The coercivity and remanent magnetization of the samples in the temperature range from 300 to 700 K linearly decrease. It is shown that the nanostructure of the alloy with the highest H corresponds to the fractal dimension D- ~ 2,3.

Optimization of Spontaneous Exchange Bias in Mn-Rich Heusler Alloys

2021 ◽  
Author(s):  
Yitian Ma ◽  
Yayi Yang ◽  
Yuan Gao ◽  
Yong Hu
Keyword(s):  
Low Temperature ◽  
Exchange Bias ◽  
Heusler Alloys ◽  
Zero Field

At low temperature, spontaneous (zero-field-cooled, SEB) and traditional (field-cooled) exchange bias effects may be induced in a series of NiMn-based Heusler alloys, and the exchange bias is commonly sensitive to...

The direct determination of magnetic domain wall profiles using a split detector STEM

1978 ◽  
Vol 36 (1) ◽  
pp. 466-467
Author(s):  
J.N. Chapman ◽  
P.E. Batson ◽  
E.M. Waddell ◽  
R.P. Ferrier
Keyword(s):  
Electron Microscope ◽  
Domain Wall ◽  
Transmission Electron Microscope ◽  
Domain Walls ◽  
Photographic Plate ◽  
Magnetic Domain ◽  
Direct Determination ◽  
Quantitative Information ◽  
Scanning Transmission Electron Microscope ◽  
Transmission Electron

By far the most commonly used mode of Lorentz microscopy in the examination of ferromagnetic thin films is the Fresnel or defocus mode. Use of this mode in the conventional transmission electron microscope (CTEM) is straightforward and immediately reveals the existence of all domain walls present. However, if such quantitative information as the domain wall profile is required, the technique suffers from several disadvantages. These include the inability to directly observe fine image detail on the viewing screen because of the stringent illumination coherence requirements, the difficulty of accurately translating part of a photographic plate into quantitative electron intensity data, and, perhaps most severe, the difficulty of interpreting this data. One solution to the first-named problem is to use a CTEM equipped with a field emission gun (FEG) (Inoue, Harada and Yamamoto 1977) whilst a second is to use the equivalent mode of image formation in a scanning transmission electron microscope (STEM) (Chapman, Batson, Waddell, Ferrier and Craven 1977), a technique which largely overcomes the second-named problem as well.

Lorentz microscopy study of magnetic domain walls in Fe-Cr-Co alloys

1978 ◽  
Vol 36 (1) ◽  
pp. 462-463
Author(s):  
Yalcin Belli
Keyword(s):  
Domain Walls ◽  
Magnetic Domain ◽  
Microscopy Study ◽  
Ferromagnetic Phase ◽  
Stable Phase ◽  
Magnetic Domains ◽  
Lorentz Microscopy ◽  
Magnetic Hardening ◽  
Electron Microscopes ◽  
Co Alloys

Fe-Cr-Co alloys have great technological potential to replace Alnico alloys as hard magnets. The relationship between the microstructures and the magnetic properties has been recently established for some of these alloys. The magnetic hardening has been attributed to the decomposition of the high temperature stable phase (α) into an elongated Fe-rich ferromagnetic phase (α1) and a weakly magnetic or non-magnetic Cr-rich phase (α2). The relationships between magnetic domains and domain walls and these different phases are yet to be understood. The TEM has been used to ascertain the mechanism of magnetic hardening for the first time in these alloys. The present paper describes the magnetic domain structure and the magnetization reversal processes in some of these multiphase materials. Microstructures to change properties resulting from, (i) isothermal aging, (ii) thermomagnetic treatment (TMT) and (iii) TMT + stepaging have been chosen for this investigation. The Jem-7A and Philips EM-301 transmission electron microscopes operating at 100 kV have been used for the Lorentz microscopy study of the magnetic domains and their interactions with the finely dispersed precipitate phases.

Temperature Dependence of Magnetic Domains and Wall Structures

1972 ◽  
Vol 30 ◽  
pp. 496-497
Author(s):  
Sonoko Tsukahara ◽  
Tadami Taoka ◽  
Hisao Nishizawa
Keyword(s):  
Temperature Dependence ◽  
Domain Walls ◽  
Magnetic Domain ◽  
Iron Film ◽  
Objective Lens ◽  
Lorentz Microscopy ◽  
Domain Structures ◽  
Wall Structures ◽  
Crystal Films ◽  
Metallurgical Structure

The high voltage Lorentz microscopy was successfully used to observe changes with temperature; of domain structures and metallurgical structures in an iron film set on the hot stage combined with a goniometer. The microscope used was the JEM-1000 EM which was operated with the objective lens current cut off to eliminate the magnetic field in the specimen position. Single crystal films with an (001) plane were prepared by the epitaxial growth of evaporated iron on a cleaved (001) plane of a rocksalt substrate. They had a uniform thickness from 1000 to 7000 Å.The figure shows the temperature dependence of magnetic domain structure with its corresponding deflection pattern and metallurgical structure observed in a 4500 Å iron film. In general, with increase of temperature, the straight domain walls decrease in their width (at 400°C), curve in an iregular shape (600°C) and then vanish (790°C). The ripple structures with cross-tie walls are observed below the Curie temperature.

Titanohematite lattice-preferred orientation and magnetic anisotropy in high-temperature mylonites

2002 ◽  
Vol 198 (1-2) ◽  
pp. 77-92 ◽  
Author(s):  
Jérôme Bascou ◽  
M.Irene B. Raposo ◽  
Alain Vauchez ◽  
Marcos Egydio-Silva
Keyword(s):  
High Temperature ◽  
Magnetic Anisotropy ◽  
Preferred Orientation ◽  
Lattice Preferred Orientation
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