scholarly journals Glass-Ceramic Synthesis of Cr-substituted Strontium Hexaferrite Nanoparticles with Enhanced Coercivity

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 924
Author(s):  
Lev A. Trusov ◽  
Anastasia E. Sleptsova ◽  
Jingtong Duan ◽  
Evgeny A. Gorbachev ◽  
Ekaterina S. Kozlyakova ◽  
...  
Keyword(s):  
Annealing Temperature ◽  
Strontium Hexaferrite ◽  
High Coercivity ◽  
Nanosized Particles ◽  
Ceramic Synthesis ◽  
Chromium Substitution ◽  
New Strategy ◽  
Magnetically Hard ◽  
Crystallization Of Glass ◽  
Hard Ferrites

Magnetically hard ferrites attract considerable interest due to their ability to maintain a high coercivity of nanosized particles and therefore show promising applications as nanomagnets ranging from magnetic recording to biomedicine. Herein, we report an approach to prepare nonsintered single-domain nanoparticles of chromium-substituted hexaferrite via crystallization of glass in the system SrO–Fe2O3–Cr2O3–B2O3. We have observed a formation of plate-like hexaferrite nanoparticles with diameters changing from 20 to 190 nm depending on the annealing temperature. We demonstrated that chromium substitution led to a significant improvement of the coercivity, which varied from 334 to 732 kA m−1 for the smallest and the largest particles, respectively. The results provide a new strategy for producing high-coercivity ferrite nanomagnets.

High-coercivity magnetic minerals in archaeological baked clay and bricks

2020 ◽  
Vol 224 (2) ◽  
pp. 1256-1271
Author(s):  
Andrei Kosterov ◽  
Mary Kovacheva ◽  
Maria Kostadinova-Avramova ◽  
Pavel Minaev ◽  
Natalia Salnaia ◽  
...  
Keyword(s):  
Parent Material ◽  
High Coercivity ◽  
Firing Process ◽  
Magnetic Minerals ◽  
Magnetic Mineralogy ◽  
Archaeological Ceramics ◽  
Mineral Phases ◽  
Initial Magnetic Susceptibility ◽  
Magnetically Hard ◽  
Saturation Remanence

SUMMARY The thorough understanding of magnetic mineralogy is a prerequisite of any successful palaeomagnetic or archaeomagnetic study. Magnetic minerals in archaeological ceramics and baked clay may be inherited from the parent material or, more frequently, formed during the firing process. The resulting magnetic mineralogy may be complex, including ferrimagnetic phases not commonly encountered in rocks. Towards this end, we carried out a detailed rock magnetic study on a representative collection of archaeological ceramics (baked clay from combustion structures and bricks) from Bulgaria and Russia. Experiments included measurement of isothermal remanence acquisition and demagnetization as a function of temperature between 20 and >600 °C. For selected samples, low-temperature measurements of saturation remanence and initial magnetic susceptibility between 1.8 and 300 K have been carried out. All studied samples contain a magnetically soft mineral identified as maghemite probably substituted by Ti, Mn and/or Al. Stoichiometric magnetite has never been observed, as evidenced by the absence of the Verwey phase transition. In addition, one or two magnetically hard mineral phases have been detected, differing sharply in their respective unblocking temperatures. One of these unblocking between 540 and 620 °C is believed to be substituted hematite. Another phase unblocks at much lower temperatures, between 140 and 240 °C, and its magnetic properties correspond to an enigmatic high coercivity, stable, low-unblocking temperature (HCSLT) phase reported earlier. In a few samples, high- and low unblocking temperature, magnetically hard phases appear to coexist; in the others, the HCSLT phase is the only magnetically hard mineral present.

scholarly journals Treatment of Strontium Hexaferrite Powder Synthesized Conventionally to Produce High Coercivity

1997 ◽  
Vol 07 (C1) ◽  
pp. C1-325-C1-326 ◽  
Author(s):  
S. A. Seyyed Ebrahimi ◽  
AJ. Williams ◽  
N. Martinez ◽  
A. Ataie ◽  
A. Kianvash ◽  
...  
Keyword(s):  
Strontium Hexaferrite ◽  
High Coercivity

Effect of annealing temperature on structural and magnetic properties of strontium hexaferrite nanoparticles synthesized by sol–gel auto-combustion method

2015 ◽  
Vol 29 (27) ◽  
pp. 1550190 ◽  
Author(s):  
Ebrahim Roohani ◽  
Hadi Arabi ◽  
Reza Sarhaddi ◽  
Saeedeh Sudkhah ◽  
Ameneh Shabani
Keyword(s):  
Crystal Structure ◽  
Thermal Decomposition ◽  
Magnetic Properties ◽  
Thermogravimetric Analysis ◽  
Annealing Temperature ◽  
Sol Gel ◽  
Combustion Method ◽  
Strontium Hexaferrite ◽  
Auto Combustion ◽  
Ft Ir

In this paper, strontium hexaferrite nanoparticles were synthesized by the sol–gel auto-combustion method. Effect of annealing temperature on crystal structure, morphology and magnetic properties of nanoparticles was investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). Also, the thermal decomposition of as-synthesized powdered samples has been studied by thermogravimetric analysis (TGA). The XRD patterns confirmed the formation of single phase M-type hexagonal crystal structure for powders annealed above 950[Formula: see text]C, whereas the presence of hematite ([Formula: see text]-Fe2O3) as secondary phase was also observed for sample annealed at 900[Formula: see text]C. Furthermore, the crystallinity along with the crystallite size were augmented with annealing temperature. Comparison of the FT-IR spectra of the samples before and after annealing treatment showed the existence of metal–oxygen stretching modes after annealing. The thermogravimetric analysis confirmed the thermal decomposition of as-burnt powders happened in three-stage degradation process. The TEM images showed the nanoparticles like hexagonal-shaped platelets as the size of nanoparticles increases by increasing the annealing temperature. With increasing annealing temperature, the magnetic saturation and the coercivity were increased to the maximum value of 74.26 emu/g and 5.67 kOe for sample annealed at 1000[Formula: see text]C and then decreased.

Magnetic Hardening of Mechanically Alloyed Pr2Co7

2012 ◽  
Vol 1471 ◽  
Author(s):  
L. Bessais ◽  
R. Fersi ◽  
M. Cabié ◽  
N. Mliki
Keyword(s):  
Magnetic Properties ◽  
Mechanical Milling ◽  
Annealing Temperature ◽  
High Vacuum ◽  
Anisotropy Field ◽  
Milling Process ◽  
Subsequent Annealing ◽  
High Coercivity ◽  
Mechanically Alloyed ◽  
Transmission Electron

ABSTRACTThe Pr2Co7 alloys are known to crystallize in two polymorphic forms: a hexagonal of the Ce2Ni7 type structure and a rhombohedral of the Gd2Co7 one. They were synthesized by mechanical milling and subsequent annealing in high vacuum. In this work, we focus on the structural study of these phases using X-ray diffraction and transmission electron microscopy. Also, we present the evolution of magnetic properties of these compounds vs the annealing temperature. The coercivity increases with annealing temperature reaching a maximum for TA = 800 °C. The highest is equal to 18 kOe at 293 K and 23 kOe at 10 K. The high magnetic properties observed in these nanostructured Pr2Co7 intermetallic alloys have their origin in its relatively high uniaxial magnetocrystalline anisotropy field, and in the homogeneous nanostructure developed by mechanical milling process and subsequent annealing. This high coercivity is attributed to the high anisotropy field of the Pr2Co7 phase and its nanoscale grain size. This leads to the formation of a magnetically hard Pr2Co7 phase.

scholarly journals INVESTIGATION OF FABRICATION OF Co-Zr BASED RARE EARTH-FREE HARD MAGNETIC ALLOYS BY MELT-SPINNING METHOD

2018 ◽  
Vol 56 (1A) ◽  
pp. 13
Author(s):  
Nguyen Van Duong
Keyword(s):  
Magnetic Properties ◽  
Rare Earth ◽  
Melt Spinning ◽  
Annealing Temperature ◽  
Xrd Analysis ◽  
Maximum Energy ◽  
Annealing Process ◽  
High Coercivity ◽  
Hard Magnetic Materials ◽  
Energy Product

Co-Zr based alloy has attracted much interest of potential to replace the rare earth-containing hard magnetic materials due to its high coercivity. In this study, we investigated the effects of subtituting elements of M (Ti, Si and Nb) and annealing temperature on the structure and magnetic properties of Co79-xZr18+x-yMyB3 alloy ribbons (x = 0 - 2, y = 0 - 4). The alloy ribbons with a thickness of 20 µm were prepared by melt-spinning method with a rolling speed of 40 ms-1. A part of the melt-spun ribbons was annealed at different temperatures from 550 to 800 oC for various durations from 2 to 15 minutes. Their structure and magnetic properties were investigated by X-ray diffraction (XRD) and a pulsed field magnetometer (PFM), respectively. The results of the XRD analysis showed that two soft magnetic phases, namely Co and Co23Zr6, coexist with a Co5Zr hard magnetic phase in the alloy ribbons. The fraction of these phases was changed with both the concentration of the subtituting elements and annealing process. Hard magnetic properties of the alloy ribbons can be strengthened significantly, namely a large coercivity Hc > 4 kOe and maximum energy product (BH)max > 3.5 MGOe were obtained with an appropriate concentration of Ti, Si or Nb and annealing process. Furthermore, the subtituting elements also affect the optimal annealing temperature for these alloys. The obtained strong hard magnetic parameters of these rare earth-free alloys are of great importance in pratical application.

scholarly journals Dominating the Structural, Microstructural and Magnetic Features of Li+ Substituted Strontium Hexaferrite (Sr1-xLi2xFe12O19)

2021 ◽  
Author(s):  
Mahmoud Hessien ◽  
Nader El-Bagoury ◽  
M. H. H. Mahmoud ◽  
M. Alsawat ◽  
Abdullah ALanazi ◽  
...  
Keyword(s):  
Annealing Temperature ◽  
Lithium Ion ◽  
Spherical Shape ◽  
Phase Evolution ◽  
Hexagonal Ferrite ◽  
Strontium Hexaferrite ◽  
X Ray Diffraction ◽  
Diffraction Profile ◽  
The Impact ◽  
Platelet Shape

Abstract Lithium ion substituted hexagonal strontium ferrite (Sr1-xLi2xFe12O19, where x= 0.1, 0.2, and 0.3) powders have been felicitously fabricated using tartrate precursor scheme. The impact of the Li+ content, as well as the annealing temperature on the phase evolution, microstructure and magnetic performance, was commanded by X-ray diffraction profile (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). Single phase hexagonal ferrite was consummated at a Li+ ratio of 0.2 and different annealing temperatures, from 1000 to 1200oC for 2h. An impurity α-Fe2O3 phase was noted at a high Li+ concentration of 0.4 and 0.6 at all temperatures. The crystallo-aspects characteristics were altered with Li+ content and annealing temperature. The microstructure of pure hexagonal ferrite sample visualized platelet like structure. A fine spherical shape displayed with platelet shape by enhancing the Li+ content up to 0.4 and 0.6. EDX analysis emphasized Fe, Sr, O, and Li atoms spread between the plate and spherical shapes. Good saturation magnetization (Ms=60.88 emu/g) was realized for Li+ content of 0.2 as the results of increasing the thickness of the nanoplatelet structure.

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