Magnetic Study on Divalent Ion Substituted Barium Hexaferrites

Magnetic properties of Co, Ni and Zn substituted barium hexaferrite (BaM) samples prepared by solid state ceramic method were studied. Saturation magnetisation were found higher for Zn-substituted BaM, whereas, coercivity is higher for Co2+ and Ni2+ ion substituted samples. Anisotropy field for all substituted samples was calculated by the law of approaching saturation. Remanence, squareness and thermomagnetic plot suggest Zn2+ ions restricts the magnetic interaction of various sites in BaM.

Magnetic hysteresis of magnetite, pyrrhotite and hematite at high temperature

Summary The magnetic properties of iron-bearing minerals at above ambient temperatures control their magnetic expression at depth in the Earth and other planets, as well as the permanent memory they retain as thermoremanence or thermochemical remanence when brought to the surface and cooled. This paper reports magnetic hysteresis parameters measured at temperatures up to the Curie point TC for natural pyrrhotite and hematite and for suites of sized magnetites, both natural and synthesized. Domain structure changes can be inferred from the ratio of saturation remanence Mrs to saturation magnetization Ms In almost all magnetites and pyrrhotites studied, Mrs decreases more rapidly with increasing measurement temperature T than Ms, indicating thermal unblocking or vortex development in single-domain grains and addition or remobilization of domain walls at high T in multidomain grains. During cooling of a rock, iron minerals might then denucleate domains or vortices. Coercive force Hc, a measure of stability against changing magnetic fields, also decreases with increasing measurement T, usually at a rate similar to that of Mrs, but often retains a finite value near the Curie point.

High-coercivity magnetic minerals in archaeological baked clay and bricks

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.

Magnetic hysteresis of 0.6–110 μm magnetites across the Verwey transition

We report saturation magnetization, Ms, saturation remanence, Mrs, coercive force, Hc, and remanence coercivity, Hcr, as a function of grain size, d, and temperature, T, for 0.6–135 μm magnetites. Five annealed and four unannealed samples were measured at 5–10 K intervals from 300 to 20 K. Mrs and Hc increase by factors of 1.5–4 in cooling through the Verwey transition (TV ≈ 120 K) and by smaller amounts around 50 K. Hysteresis properties change continuously over ≈20 K below TV or for annealed 0.6, 3, and 6 μm grains, within ≈10 K below TV. Hc(d) changes for annealed magnetites from ∼d–0.5 at 300 K to ∼d–0.6–d–0.7 at 120–130 K to ∼d–0.3 at 80–100 K. Day plots of Mrs(T)/Ms(T) versus Hcr(T)/Hc(T) indicate major domain structure changes with T, e.g., 6 μm grains change from large pseudo-single-domain (PSD) at 300 K to multidomain (MD) just above TV and return to PSD below TV, evolving to higher Mrs and Hc down to 20 K. Hysteresis loops change from normal at 300 K to slightly constricted near TV to severely constricted below 50 K. We interpret these results in the light of electron microscopic observations by Kasama et al. (2010 , 2012) . Hardening of magnetic hysteresis below TV and the evolution from MD to PSD, and even to single-domain in the finest grains, results from subdivision of grains by monoclinic twinning, reduced magnetic domain sizes in monoclinic magnetite, and confinement of magnetic domains within twin domains. Constricted hysteresis loops indicate coexisting magnetically hard and soft phases, initially growing monoclinic regions and residual cubic magnetite.

Efek Penambahan Fe3Mn7 Terhadap Sifat Fisis dan Mekanik α-Fe2O3

Abstrak: Preparasi dan karakterisasi pellet α-Fe2O3 dengan penambahan 0, 2, 5 dan 10 %wt. Fe3Mn7 berbasis pada materialalam telah berhasil dilakukan. Proses pencampuran serbuk α-Fe2O3 dan Fe3Mn7 dilakukan dengan menggunakan HEM. ºKemudian campuran serbuk dikasinasi pada suhu 1000C, dikompaksi pada 69 Pa hingga menjadi pellet dan disinter padasuhu 1000 ºC. Karakterisasi XRD menunjukkan adanya fasa dominan α-Fe2O3 dan fasa baru MnO2 dan Fe3O4. Densitas dankekerasan sampel meningkat secara linier seiring dengan kenaikan komposisi Fe3Mn7 yang ditambahkan. Sampel optimum3diperoleh pada sampel α-Fe2O3/10 %wt. Fe3Mn7 dengan nilai bulk density dan kekerasan masing-masing 4,98 g/cm and994,94 HV. Sampel ini termasuk dalam klasifikasi hard magnet dengan nilai magnetisasi saturasi, remanen dan koersivitasmasing-masing sebesar 24,0 emu/g, 10,3 emu/g dan 571,8 Oe.Kata kunci:. α-Fe2O3, Fe3Mn7, densitas, kekerasan, sifat magnetikAbstract: Preparation and characterization of α-Fe2O3 pellet with the addition of 0, 2, 5 and 10 %wt. Fe3Mn7 based on naturalmaterials have been successfully carried out. The process of mixing powder of α-Fe2O3 and Fe3Mn7 was performed usingºHEM. Then, the mix powders were calcined at temperature of 1000 C. After that, the powders were compacted at 69 Pa intopellet and sintered at temperature of 1000ºC. Characterization of XRD shows that the samples have major phase of α-Fe2O3and new phases of MnO2 and Fe3O4. The density and hardness samples increase linearly with increasing of Fe3Mn73composition. The optimum sample with α-Fe2O3/10 %wt. Fe3Mn7 has bulk density and hardness value of 4.98 g/cm and 994.94HV respectively. This sample is classified as semi-hard magnet with magnetization saturation, remanence and coercivity valueof 24.0 emu/g, 10.3 emu/g dan 571.8 Oe respectively.Keywords: α-Fe2O3, Fe3Mn7, density, hardness, magnetic properties

Magnetic Bacteria as a Tool for Bioremediation of Heavy Metal Ion

Magnetotactic bacteria (MTB) are microorganism found in lake sediments and have a chain like organelle called magnetosome which is composed of highly pure crystal of magnetite (Fe3O4). We culturedMagnetospirillum magnetotacticum(MS-1) with culture media containing heavy metal ions such as Fe (standard media), Fe/Zn or Fe/Co and study on a possibility of MTB as a tool for bioremediation. In culture media containing Fe, Fe/Zn or Fe/Co, the growth rate of the bacteria was almost same. We measured the magnetic properties of the dried cells. The saturation magnetization (Ms) and the saturation remanence (Mr) of MS-1 cultured in Fe/Zn or Fe/Co media were decreased, but the coercivity (Hc) and the coercivity remanence (Hr) were increased from those of MS-1 cultured in the Fe media. The value ofMr/MsandHr/Hcwere ca. 0.5 and ca. 1.0, respectively. The changes in the magnetic properties of MS-1 cultured in Fe/Zn or Fe/Co media represent that MS-1 would take not only Fe, but also Zn or Co element in their environment. We discuss about a possible usage and advantages of MTB as a tool for bioremediation.

Effect of Mechanical Stresses on Coercive Force and Saturation Remanence of Ensemble of Dual-Phase Interacting Nanoparticles

In the dual-phase model of interacting nanoparticles stretching leads to a decrease in both coercive force Hc and saturation remanence Irs , and compression — to their growth. Magnetostatic interaction between particles also decreases both Hc and Irs . Theoretical analysis was carried out in the framework of the dual-phase system of interacting particles on the example of nanoparticles γ-Fe2 O3, epitaxially coated with cobalt.

A paleomagnetic test for northward tectonic transport of the eastern Selwyn Basin, northern Canadian Cordillera: data from the mid-Cretaceous Ragged Pluton

Ragged Pluton is a member of the Tungsten Plutonic Suite in the eastern Selwyn Basin. This circular massive 97 Ma granitic pluton is ∼5 km in diameter. It intrudes deformed and metamorphosed clastic strata of the Neoproterozoic to Lower Cambrian Vampire Formation. Thermal and alternating field step demagnetization data for 216 specimens from 21 plutonic sites isolated a stable characteristic remanent magnetization (ChRM) direction at 20 sites of declination D = 325.9°, inclination I = 80.4° (α95 = 2.7°, k = 142). Thermal demagnetization and saturation remanence analysis show that the ChRM is carried by both single-domain pyrrhotite and magnetite. Ragged Pluton’s paleopole at 73.9°N latitude, 191.4°E longitude (dp = 5.0°, dm = 5.2°) is concordant with its co-eval 97 Ma North American reference paleopole, showing at 95% confidence that the pluton has not been significantly rotated or translated relative to North America. This paleomagnetic result favours tectonic models in which the eastern Selwyn Basin is autochthonous, or nearly so, since the mid Cretaceous.