Hysteresis and coercivity of hematite

Journal of Geophysical Research: Solid Earth - Tập 119 Số 4 - Trang 2582-2594 - 2014
Özden Özdemir1, David J. Dunlop1
1Geophysics Department of Physics University of Toronto Toronto Ontario Canada

Tóm tắt

AbstractIn room‐temperature hysteresis, 14 submicron hematites (0.12‐0.45 µm) had large coercive forces Hc (150‐350 mT), while 22 natural 1‐5.5 mm hematite crystals had Hc = 0.8‐23 mT (basal‐plane measurements). Single‐domain (SD) and multidomain (MD) hematites owe their high Hc mainly to magnetoelastic anisotropy, caused in fine particles by internal strains and in large crystals by defects like dislocations, with a smaller contribution by triaxial magnetocrystalline anisotropy. A strong correlation between Hc and the defect moment Md measured below hematite's Morin transition also favors magnetoelastic control. Saturation remanence/saturation magnetization ratios Mrs/Ms and coercivity ratios Hcr/Hc (Hcr is remanent coercive force) are distinctive: Mrs/Ms = 0.5‐0.9, Hcr/Hc = 1.02‐1.17 for MD hematites; Mrs/Ms = 0.5‐0.7, Hcr/Hc = 1.45‐1.62 for SD hematites. In high‐temperature (20‐690°C) hysteresis, Hc(T) ~ Ms(T) to a power 1.8‐2.4 above 385°C. Magnetoelastic wall pinning by crystal defects is thus more likely than control by domain nucleation which depends on magnetocrystalline anisotropy. Our results compare well with existing Hc vs. crystal size d data. A suggested peak in Hc around 15 µm and a proposed slope change around 100 µm are both questionable. Using only near‐saturation data, Hc varies continuously as d−0.61 from ≈0.1 µm to 2 mm. The SD threshold size d0 may be >15 µm but there is no strong evidence that d0 ≈100 µm. Direct domain observations are needed to settle the question. Augmented data sets for Hc and Mrs vs. d show that SD hematite is increasingly affected by thermal fluctuations below ≈0.3 µm and generally confirm a superparamagnetic threshold size ds of 0.025‐0.03 µm.

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Tài liệu tham khảo

Acklin B., 2012, Magnetic Nanoparticles: Properties, Synthesis and Applications

10.1186/1556‐276X‐7‐144

10.1038/physci232015a0

10.1016/j.jcrysgro.2011.05.030

10.1007/s00339‐010‐5983‐7

10.1103/PhysRevB.61.6826

10.1002/cphc.200600130

10.1063/1.2830699

10.1051/jphysrad:01951001203017200

10.1051/anphys/194311180258

10.1098/rsta.1957.0016

10.1111/j.1365-246X.1961.tb02925.x

10.1111/j.1365-246X.1981.tb02676.x

10.1016/0031-9201(77)90108-X

10.1046/j.0956-540x.2001.01443.x

10.1080/14786437008238425

10.1126/science.169.3948.858

Dunlop D. J., 1971, Magnetic properties of fine‐particle hematite, Ann. Geophys., 27, 269

10.1029/2001JB000486

10.1029/2001JB000487

10.1017/CBO9780511612794

10.1063/1.1658162

10.1139/p71-335

10.1016/0375-9601(68)90522-7

10.1080/14786436508224935

10.1080/14786436408222959

Flanders P. J., 1965, Proc. Int. Conf. Magnetism Nottingham, 594

10.1016/0031-9163(62)90081-1

10.1098/rspa.1968.0067

10.1002/9783527627561

10.1016/j.matlet.2010.10.001

10.1029/93JB01228

10.1029/98JB00958

10.1016/j.matlet.2009.09.054

Irving E., 1964, Palaeomagnetism and its Applications to Geological and Geophysical Problems

10.1016/S0031-9201(01)00271-0

10.1063/1.1714243

10.1016/j.pepi.2010.08.008

10.1016/j.jssc.2005.06.018

10.1007/s00531‐011‐0665‐z

10.1002/ggge.20245

10.1016/j.colsurfa.2010.05.039

Morrish A. H., 1994, Canted Antiferromagnetism: Hematite

10.1029/92JB01846

10.1029/2002GL015597

10.1029/2005JB003820

10.1029/2006JB004555

10.1029/2008GC02110

10.1088/0022-3727/36/13/201

10.1016/S1474-7065(03)00120-7

10.1063/1.1709904

10.1017/CBO9781139170383

10.1063/1.125572

10.1016/j.solidstatesciences.2010.08.020

10.1016/j/matlet.2010.06.025

Sunagawa I., 1960, Growth history of hematite, Am. Mineral., 45, 566

10.1080/14786436508230080

10.1016/j.jallcom2011.04.117

10.1201/b11760

10.1016/j.jallcom.2007.07.115

10.1016/j.matlet.2010.12.053

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Thông tin xuất bản

Journal of Geophysical Research: Solid Earth

Tập 119 Số 4

2582-2594

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