Sensitive SQUID magnetometry for studying nanomagnetism

Sawicki, M.; Stefanowicz, W.; Ney, A.

doi:10.1088/0268-1242/26/6/064006

Cited by 174 publications

(152 citation statements)

References 32 publications

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“…Subsequently, M(T ) is measured from 300 to 2 K at 10 mT (FC). The diamagnetic background of the substrate, derived from high-field M(H ) data at 300 K, has been subtracted from all magnetization data [15]. Finally, to determine the majority carrier type of the samples, the sign of the Seebeck coefficient has been determined using an ordinary hot tip (360 • C)/cold tip (RT) setup on Ohmic gold contacts in a 5 mm × 5 mm van der Pauw geometry.…”

Section: Methodsmentioning

confidence: 99%

Local structure and magnetism of Co3+ in wurtzite Co:ZnO

et al. 2017

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The structural and magnetic properties of 30% and 50% Co-doped ZnO have been investigated in order to determine the influence of the presence of Co 3+ as a potential p-type dopant. For 30% doping, Co 3+ could be stabilized in the wurtzite lattice of ZnO without phase separation by providing high oxygen partial pressures during growth. At 50% Co concentration, the crystal lattice destabilizes. X-ray absorption spectroscopy and simulations are used to substantiate the valence and local structure of Co 3+ . Integral and element selective magnetometry reveals uncompensated antiferromagnetism of the Co atoms irrespective of being present as Co 2+ or Co 3+ .

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Section: Methodsmentioning

confidence: 99%

Local structure and magnetism of Co3+ in wurtzite Co:ZnO

et al. 2017

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“…The very weak magnetization not only limits the practical applications, but also raises questions on the fundamentals of defect induced ferromagnetism. On the one hand, measurement artifacts in SQUID magnetometry may occur: improper mounting of samples and wrong use of sample holders can easily generate ferromagnetic like signal [32][33][34]. On the other hand, the debate over the purity of graphite and oxide substrates continues in parallel [35][36][37][38][39].…”

Section: Introductionmentioning

confidence: 99%

Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism

et al. 2015

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Defect-induced ferromagnetism has triggered a lot of investigations and controversies. The major issue is that the induced ferromagnetic signal is so weak that it can sufficiently be accounted for by trace contamination. To resolve this issue, we studied the variation of the magnetic properties of SiC after neutron irradiation with fluence covering four orders of magnitude. A large paramagnetic component has been induced and scales up with defect concentration, which can be well accounted for by uncoupled divacancies. However, the ferromagnetic contribution is still weak and only appears in the low fluence range of neutrons or after annealing treatments. First-principles calculations hint towards a mutually exclusive role of the concentration of defects: a higher defectconcentration favors a larger magnetic interaction at the expense of spin polarization. Combining both experimental and first-principles calculation results, the defect-induced ferromagnetism can probably be understood as a local effect which cannot be scaled up with the volume. * Electronic address: s.zhou@hzdr.de 2

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“…6,7 Recently, we have correlated the observed ferromagnetism in ZnO with the presence of secondary Co-rich phases. 8 These conclusions about the intrinsic magnetic properties of Co:ZnO relied on avoiding measurement artefacts when performing very sensitive superconductive quantum interference device (SQUID) magnetometry 9 in combination with synchrotron-based x-ray absorption spectroscopy (XAS), x-ray linear dichroism (XLD), and x-ray magnetic circular dichroism (XMCD). 5 The detection of small quantities of local structural or chemical variations using these techniques poses a significant analytical challenge and is ideally complemented by the application of advanced transmission electron microscopy (TEM) techniques to the same materials.…”

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confidence: 99%

Defects in paramagnetic Co-doped ZnO films studied by transmission electron microscopy

Kovács

Ney

Duchamp

et al. 2013

Journal of Applied Physics

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Room-temperature ferromagnetic Co-doped ZnO nanoneedle array prepared by pulsed laser deposition Appl. Phys. Lett. 87, 173119 (2005) We study planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al 2 O 3 ), as well as the Co:ZnO/Al 2 O 3 interface, using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy. Co:ZnO samples that were deposited using pulsed laser deposition and reactive magnetron sputtering are both found to contain extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3-4 Co:ZnO layers next to the Al 2 O 3 substrate. The stacking fault density is in the range of 10 17 cm À3 . We also measure the local lattice distortions around the stacking faults. It is shown that despite the relatively high density of planar defects, lattice distortions, and small compositional variation, the Co:ZnO films retain paramagnetic properties. V C 2013 AIP Publishing LLC.

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Sensitive SQUID magnetometry for studying nanomagnetism

Cited by 174 publications

References 32 publications

Local structure and magnetism of Co3+ in wurtzite Co:ZnO

Local structure and magnetism of Co3+ in wurtzite Co:ZnO

Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism

Defects in paramagnetic Co-doped ZnO films studied by transmission electron microscopy

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