Magnetic Characterization of Iron Oxide Nanoparticles

Conclusions for Measurements at Room Temperature

2. Addition of Terbium leads to the formation of more hematite by oxidizing maghemite, shown by higher coercivity (Fig. 1 & 2). 3. Presence of superparamagnetic (SP) and single domain (SD) maghemite and high coercivity hematite. Grains are close to SP/SD size boundary, since lengthening averaging time decreases coercivity. Grain interaction is minimal as seen from narrow distribution along Hu

Introduction that can destroy cancerous cells [Teleki 2009]. Important is an exact characterization of the materials being used. In this interdisciplinary study common methods from rock magnetism are used to characterize the magnetic properties of iron oxide

Materials – Flame spray pyrolysis was used to synthesize the maghemite (γ-Fe(III)2O3

Princeton Measurements Corporation vibrating sample magnetometer(VSM) at the LNM.

Acquisition of Isothermal Remanent Magnetization (IRM)

the acquisition curve provides information on the coercivity spectra which is dependent on material concentration and grain size.For Mgh10_0 the acquisition shows rapid increase in relatively low

[Dunlop 1997]. Samples Mgh15_0, Mgh15_5 and Mgh15_10 acquire an IRM more slowly. Although the IRM has a low coercivity component, samples are not saturated by 1000mT. Mgh15_20 has only a high coercivity component to the magnetization.

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Induced Magnetization as a Function of Field (Hysteresis Loops)

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Figure 2: If a material contains two magnetic phases, one with a high coercive force and one with a low coercive force, the hysteresis loop will be smaller at the origin (wasp-waisted). Mgh15_0, Mgh15_5, Mgh15_10 and Mgh15_20 show this behavior.

First-Order Reversal Curves (FORCs)

cdistribution moves to lower coercivities with longer averaging time.

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LNM ETH Zurich Laboratory for Natural Magnetism

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Hysteresis as Function of Temperature

Jara Schnyder, Universität Zürich, jaraschnyder@access.uzh.chSupervisors: A.M. Hirt, Institut für Geophysik ETH Zürich

G. Sotiriou, Institut für Verfahrenstechnik ETH Zürich

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Figure 4: Magnetic hysteresis after annealing in He to progressively high temperatures for Mgh15_0. Hysteresis was repeated at room tempera-ture after selective heating steps. Hysteresis loops at a) 25°, 100°, 200°, 300°; b) 300°, 25°; c) 400°, 500°, 25°; d) 600°, 25°; e) 700°, 25°; f ) 800°, 25°, where as returning to room temperature recovers the original magnetic state for all heating steps up to 700°.

a) b) c) d) e) f )

Conclusions for High-temperature Measurements1. Ms and Hc decrease with increasing temperature as would be expected. Due to high temperature the samples relax more quickly and there is a loss in magnetization and coercivity (Fig. 4 & 5a & 6).

3. Addition of Tb to the maghemite particles leads to a change in the magnetic behavior during heating in a limited temperature range between 100

accompanied by an increase in both Ms and Hc. To verify this explanation we will perform XRD at temperature.

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Figure 7: An example of hysteresis at increasing temperatures for Mgh15_10 with room temperature loops after each heating. Hysteresis at a) 25°, 100°, 25°; b) 200°, 25°; c) 300°, 25°; d) 400°, 25°; e) 600°, 25°; f ) 800°, 25°. Ms decreases with increasing temperature, whereas between 100° and 200° a exagerated wasp-waisting occurs; this is indicative for the formation of a new magnetic phase. A large vertical shift at room temperature is

Figure 6: a) Coercivity (Hc) vs. temperature of Mgh15_0; b) Saturation magnetization (Ms) vs. temperature of Mgh15_0.

-ture during annealing. a) Mgh15_0; b) Mgh15_10.

Acknowledgements: I thank Hans-Peter Haechler for helping handling the VSM. References: 21:2094-2100. Dunlop, D.J., and Ö.Özdemir, 1997. Rock Magnetism: Fundamentals and Frontiers, 573 pp., Cambridge University Press, New York, London and Cambridge.

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