In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

http://quebec.hwr.arizona.edu/classes/hwr696t/gosse01-cosmogenic-nuclide-review.pdf

Terrestrial in situ cosmogenic nuclides: theory and application

Proceedings of the Ocean Drilling Program

[1] Although most paleomagnetic and environmental magnetic papers incorporate a Day plot of the hysteresis parameters Mrs/Ms versus Hcr/Hc, a comprehensive theory covering superparamagnetic (SP), single-domain (SD), pseudo-single-domain (PSD), and multidomain (MD) (titano)magnetites is lacking. There is no consensus on how to quantify grain-size trends within the Day plot, how to distinguish MD from SP trends/mixtures, or whether magnetite, titanomagnetites, and other minerals have distinctive trends by which they might be identified. This paper develops the theory of the Day plot parameters for MD, MD + SD, PSD, and SP + SD grains of titanomagnetite (Fe 3– xTixO4) with compositions x = 0 (TM0 or magnetite) and x = 0.6 (TM60). MD grains have a separate trend that intersects the curve for SD + MD mixtures. SP + SD mixtures generate a variety of trends, depending on the SP grain size. All SP + SD curves lie much above those for MD or SD + MD trends, as has been proposed, but not demonstrated, previously. Data for PSD-size magnetites of many different origins fall along a single trend, but different levels of internal stress shift points for similar grain sizes along the ‘‘master curve.’’ In order to use the Day plot to determine grain size, one must have independent information about the state of internal stress. Theoretical model curves for SD + MD mixtures match the PSD magnetite and TM60 data quite well, although the SD!MD transition region in grain size is much narrower for TM60 than for magnetite. The agreement between PSD data and SD + MD mixing curves implies that PSD behavior is due to superimposed independent SD and MD moments, either in individual or separate grains, and not to exotic micromagnetic structures such as vortices. The theory also matches Mrs and Hc values in mechanical mixtures of very fine and very coarse grains, although nonlinear mixing theory is required to explain some Hcr and Hcr/Hc data. INDEX TERMS: 1540 Geomagnetism and Paleomagnetism: Rock and mineral magnetism; 1594 Geomagnetism and Paleomagnetism: Instruments and techniques; 1533 Geomagnetism and Paleomagnetism: Remagnetization; 1512 Geomagnetism and Paleomagnetism: Environmental magnetism;

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JB000486

Theory and application of the Day plot (Mrs/Ms versus Hcr/Hc) 1. Theoretical curves and tests using titanomagnetite data

2.3. Amorphous Minerals 4354 3. Biological Routes to Controlling Morphology 4354 3.1. General Mechanisms 4356 3.1.1. Soluble and Insoluble Organic Molecules 4356 3.1.2. Control over Crystal Polymorph 4357 3.1.3. Control over Crystal Orientation 4359 3.2. Single-Crystal Biominerals 4359 3.2.1. Organic and Inorganic Soluble Additives 4360 3.2.2. Templating of Single-Crystal Morphologies 4361 3.3. Polycrystalline Biominerals 4366 3.3.1. Nacre Formation in Mollusks 4366 3.3.2. ForaminiferasA Biogenic Mesocrystal 4368 3.4. Amorphous Biominerals 4370 3.4.1. Silicification in Diatoms 4370 3.4.2. In Vitro Studies of Silicification in Diatoms 4371 4. Bioinspired Routes to Controlling Crystal Morphologies 4371

Controlling Mineral Morphologies and Structures in Biological and Synthetic Systems

A comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials: Some results from lake sediments

[1] In environmental magnetism, rock and mineral magnetic techniques are used to investigate the formation, transportation, deposition, and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes. All materials respond in some way to an applied magnetic field, and iron-bearing minerals are sensitive to a range of environmental processes, which makes magnetic measurements extremely useful for detecting signals associated with environmental processes. Environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics, chemistry, and biology and environmental science, including research on climate change, pollution, iron biomineralization, and depositional and diagenetic processes in sediments to name a few applications. Magnetic parameters are used to routinely scan sediments, but interpretation is often difficult and requires understanding of the underlying physics and chemistry. Thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities, complexities, and limitations to interpretations. In this review, we evaluate environmental magnetic parameters based on theory and empirical results. We describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations. We also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology, chemistry, and physics. Finally, we discuss directions in which environmental magnetism is likely to develop in the future.

/pdf/environmental-magnetism-principles-and-applications-42hbntvvit.pdf

Environmental magnetism: Principles and applications

This is an updated collation of magnetic parameters of rocks and minerals for geologists, geochemists, and geophysicists. Since the publication of the previous edition of Handbook of Physical Constants [74], two other collations have appeared [16, 18]. In addition, selected magnetic parameters have also been assembled [19, 22, 38, 41, 88]. Rather than produce a fully comprehensive collection, we have aimed for high-precision data obtained from wellcharacterized samples. Both tables and figures have been used for presenting the data, and best-fit equations have been provided for some of the displayed ata so that interpolations can be made easily. In an attempt to discourage the use of the outdated cgs system, all values are in the SI system (see Moskowitz, this volume). References have been cited for the sources used here. However, a more comprehensive bibliography has also been provided from which information can be extracted for samples which have not been included. The single-crystal constants and their variation with temperature and composition are for use by rock magnetists. Paleomagnetists and magnetic anomaly modelers have been provided with the magnetic properties of rocks and polycrystalline mineral samples. Lastly, we have made an effort to address the needs of environmental magnetism, a new group of researchers who require the values of sizeand

http://www.alaska-gold.com/RF003p0189.pdf

Magnetic Properties of Rocks and Minerals

Most observers of the geophysical scene, those involved with plate tectonics and continental drift in particular, are aware of the seminal contributions of rock magnetism and its sister discipline, paleomagnetism, which some have called “applied rock magnetism.” That was in the heady days of the 1960s. As a discipline, however esoteric, rock magnetism goes further back to the 19th century when the Swedish prospectors for iron ores and Italian and German paleomagnetists in search of the history of the geomagnetic field were using rock magnetism as an exciting new tool. The first book on rock magnetism, Der Gesteinsmagnetismus by H. Haalck, was published in 1942, more than a decade before T. Nagata's Rock Magnetism, cited by Dunlop and Ozdemir as the earliest work on the subject. There have been more recent volumes on the subject, including one that I coauthored with Frank Stacey. However, I am not exaggerating when I say that Rock Magnetism: Fundamentals and Frontiers leaves the others in the dust.

Rock Magnetism: Fundamentals and Frontiers

We have developed a rapid method of characterizing the fine-scale variation (sub-micron to hundreds of microns, µm) in the grain size of magnetite in long sediment cores. This method is a new rock magnetic tool and can be readily applied to the following disciplines: (1) environmental studies; (2) hydrology; (3) petrology; and (4) geomagnetism.

The method consists of a comparative plot of the depth variation of two magnetic parameters. The first parameter, low field (less than 0.1 millitesla, mT, or 1 Oe) susceptibility in a steady field is plotted on the abscissa. The second parameter, anhysteretic remanent magnetization (ARM) imparted by a smoothly decreasing AF of peak value 100 mT (1,000 Oe) in the presence of a weak steady field (0.01-0.1 mT, or 0.1-1 Oe) is plotted on the ordinate. For a sediment column in which the magnetic mineral is magnetite, a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points (χ, ARM).

Subir K. Banerjee

Papers

A comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials: Some results from lake sediments

Environmental magnetism: Principles and applications

Magnetic Properties of Rocks and Minerals

Rock Magnetism: Fundamentals and Frontiers

A rapid method for magnetic granulometry with applications to environmental studies