It was the purpose of this thesis to contribute to a better understanding of spin caloritronic phenomena and thermoelectric effects as well as the anisotropy of magnetic thin films. Mostly this work was motivated by the recent discovery of the spin Seebeck effect (SSE) in Japan: a generation of a pure spin current across the interface between magnetic|nonmagnetic materials upon application of the temperature gradient along (transversal SSE) or across (longitudinal SSE) the interface. As the experimental configuration for the TSSE involves the heat flows, special care to spurious temperature gradients has to be taken. Semiconducting GaMnAs and insulating yttrium iron garnet (YIG) magnetic thin films were investigated. As nonmagnetic material platinum was chosen, providing also the opportunity to detect pure spin currents via the spin Hall effect (SPHE) in it. Starting with the measurement of in-plane voltages, transverse to the in-plane temperature gradient and measured along the platinum stripes, by sweeping the external magnetic field at different in-plane directions (TSSE geometry), symmetric and asymmetric contributions were observed in both, the GaAs/GaMnAs/Pt and GaAs/GaMnAs systems. The former was clearly attributed to the planar Nernst effect, arising from an in-plane temperature gradient along the sample, while the latter was shown to be result of the anomalous Nernst effect (ANE) caused by spurious out-of-plane temperature gradients. Using the ANE constant that was measured upon deliberately applying an out-of-plane temperature gradient, it was estimated that a rather small temperature drop of ΔT z ≈ 12 nK across the 200 nm magnetic film thickness can be responsible for the appearance of spurious ANE signals, leading to the asymmetry of the thermovoltages registered in the PNE/TSSE configuration. Thus, the TSSE if it exists at all in the GaMnAs sample, is very likely to be negligible. The transport measurements in the insulating YIG sample in TSSE/PNE configuration demonstrated no field dependencies, supporting the idea that the signals in the semiconducting GaMnAs film originated not from the TSSE, but rather from the conventional ANE. The voltages in ANE/LSSE configuration the characteristic LSSE signals were observed. This thesis is also devoted to the magnetic anisotropy investigation in GaMnAs thin film by applying wide-field Kerr microscopy simultaneously to galvanomagnetic measurements. Upon sweeping the magnetic field the development of magnetic domains was traced: at low temperatures (5 K) the sample exhibits a clear two-fold switching of magnetization, while at higher temperatures (above 20 K) only a one-step switching was detected, indicating a strong temperature dependence of the magnetic anisotropy. The same behavior was derived from the transport measurements in the PHE configuration. Rotating the field in the plane of the thin film and analyzing the resulting angle dependencies of the transversal voltage, we obtained the anisotropy constants K u and K c . The temperature dependence of the K u / K c -ratio showed a gradual substitution of the cubic anisotropy, prevailing at low temperatures, by a uniaxial one with rising temperature. For the purpose of the magneto-optical investigation and in-depth analysis of the magnetic anisotropy, within the frame of this thesis a new hardware and software realization for quantitative Kerr microscopy was developed. The principles of such a technique were formulated already years ago by Rave et al, but the experimental realization was limited to materials with in-plane surface magnetization and static domain imaging due to the manual adjustment of the microscope sensitivity. The realization of a separation of in-plane|out-of-plane magnetic contrast, suggested in this thesis, disposes those complications and improves the method, providing the opportunity for a simultaneous measurement of both components of magnetization in an automatic regime and, thus, allowing the quantitative analysis of the magnetization reorientation processes in magnetic media. This technique was successfully applied to the quantitative investigation of the magnetic domain structure in GaMnAs film, and was also demonstrated on a number of other materials, including a permalloy (Ni 81 Fe 19 ) patterned film element and the separation of the in-plane and out-of-plane components of magnetic contrast in sintered NdFeB polycrystals. In summary, this work contributes to a deeper understanding of the contribution of the conventional thermoelectric effects to the exploding field of spin caloritronic. It points out that thermoelectric phenomena have to be treated with care and that magnetic anisotropy and its temperature dependence have to be considered in any analysis of spin caloritronic phenomena. The thesis extends the existing methods of investigating magnetic anisotropy of magnetic films by introducing a novel technical realization of quantitative Kerr microscopy.

In this thesis, specific heat, magnetic susceptibility and resistivity studies on the iron-pnictide superconductors LiFeAs, NaFe1-xCoxAs, AFe2As2 (A = K, Ca, Ba), M1-xNaxFe2As2 (M = Ca, Ba), and Ca(Fe1-xCox)2Fe2As2 are presented, from which different intrinsic physical properties are resolved. The combined first-order spindensity wave/structural transition which occurs in the parent compounds of the 122 pnictide systems is shown to gradually shift to lower temperature for low doping levels. Upon higher doping, this transition is completely suppressed and simultaneously, superconductivity appears at lower temperature. In contrast, the phase diagram in Ca(Fe1-xCox)2Fe2As2 is shown to exhibit a pronounced region of coexistence of magnetism and superconductivity. Further important results reported in this work concern the electronic properties and superconducting-gap characteristics. In LiFeAs, the zero-field temperature dependence of the electronic specific heat can be well described by two s-wave gaps, whose magnitudes are in agreement with ARPES results. Our gap analysis in KFe2As2, Ca0.32Na0.68Fe2As2, and Ba0.65Na0.35Fe2As2 single crystals also implies the presence of two s-wave-like gaps. The magnetic phase diagram of LiFeAs and KFe2As2 for magnetic fields along both principal orientations has been constructed and an anisotropy of Hc2(T) of 3 and 5, respectively, has been obtained.

In my work, magnetic and structural transitions of three categories of compounds are investigated by density functional calculations under local spin density approximation (LSDA). The first compound is Rh2MnGe with full Heusler structure at ambient condition. However, the structure is unstable at T=0 according to our calculations. A more stable structure we found is tetragonal one with either extension or compression along c-axis. The electronic reason of this distortion is the band Jahn-Teller effect where the Jahn-Teller active states are 4d states of Rh which is accidently put at the Fermi level by spin splitting. Then, magnetic moment behavior under pressure in itinerant compounds is investigated in four cubic Laves phase compounds (YFe2, ZrFe2, HfFe2, and LuFe2). The magnetic spin moment is decreased under pressure. A magnetic collapse where the spin moment vanishes is predicted under pressure around 20 GPa for Zr and Hf compounds, 40 GPa for Y and Lu compounds. The behavior of the magnetic moment is the result of competition between magnetic exchange interactions and kinetic energy during the compression of the volume, as described by the Stoner model. The last material investigated is CoO using LDSA+U in order to describe the strong Coulombic interaction of the transition metal ion. The pressure induced a magnetic transition, which was discovered in experiments, is explained by the competition between ligand field splitting and exchange energy. The ligand field splitting is increased under pressure, and suppresses the intraatomic exchange. As a result, the spin state changes from high spin to low spin, and at last to nonmagnetic state.

Thin films and nanowires of Co-Pt have been prepared by means of electrodeposition. Composition, structure, microstructure and magnetic properties have been intensively studied using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry and correlated to the deposition parameters such as electrolyte composition, deposition current and/or potential. Co rich Co-Pt films have been deposited at various current densities. A nearly constant composition of Co70Pt30 was achieved for current densities between 18 and 32 mA/cm². Detailed texture measurements confirmed an increasing fraction of the hexagonal phase with its c-axis aligned perpendicular to the film plane with increasing current density. Accordingly, magnetic properties are strongly affected by the magnetocrystalline anisotropy of the hexagonal phase that competes with the shape anisotropy of the thin film geometry. Co-Pt nanowires have been prepared within alumina templates at different deposition potentials between -0.6 and -0.9VSCE changing the composition from nearly pure Pt to Co. The composition Co80Pt20 was observed at a deposition potential of -0.7VSCE. Co-Pt nanowires are nanocrystalline in the as-deposited state. Magnetic measurements reveal changing fcc and hcp phase fractions within the wires as the effective anisotropy significantly differs from the expected shape anisotropy for nanowires with high aspect ratio. This change in effective anisotropy is attributed to the preferential alignment of the c-axis of hcp Co-Pt phase perpendicular to the nanowires axis. A promising alternative with much smaller feature sizes is the diblock copolymer template. Electrodeposition of Co and Co-Pt into these templates has been carried out. Inhomogeneities in the template thickness as well as a certain substrate roughness have been identified to be the reasons for inhomogeneous template filling. Thus magnetic properties are dominated by large deposits found on top of the template. Additionally, rolled-up tubes of several nm thick Au/Co/Au films have been characterized magnetically. Temperature dependent measurements show an exchange bias behaviour that is explained in terms of induced stresses during cooling. Changes of magnetic properties in the investigated samples are finally discussed in terms of competing effects of different magnetic anisotropies in various geometries. / Co-Pt Dünnschichten und Nanodrähte wurden mittels elektrochemischer Abscheidung hergestellt. Zusammensetzung, Struktur, Mikrostruktur und magnetische Eigenschaften wurden intensiv mit Röntgenbeugung, Rasterelektronenmikroskopie und Magnetometrie untersucht und mit den Depositionsparametern wie Elektrolytzusammensetzung, Abscheidestrom und/oder-potential korreliert. Co reiche Co-Pt-Filme wurden mit verschiedenen Stromdichten hergestellt. Eine nahezu konstante Zusammensetzung im Bereich Co70Pt30 wurde für Stromdichten zwischen 18 und 32 mA/cm² erreicht. Detaillierte Texturmessungen bestätigen einen zunehmenden Anteil an hexagonaler Phase mit senkrecht zur Filmebene ausgerichteter c-Achse mit zunehmender Stromdichte. Dementsprechend werden die magnetischen Eigenschaften stark von der magnetokristallinen Anisotropie der hexagonalen Phase beeinflusst, die mit der Formanisotropie der Dünnschicht-Geometrie konkurriert. Co-Pt-Nanodrähte wurden in nanoporöse Aluminiumoxidmembranen bei verschiedenen Potentialen zwischen -0,6 und -0.9 VSCE abgeschieden, wobei sich die Zusammensetzung von nahezu reinem Pt zu Co verändert. Die Zusammensetzung Co80Pt20 wurde bei einem Abscheidepotential von -0.7 VSCE erhalten. Die so hergestellten Co-Pt Nanodrähte sind nanokistallin. Magnetische Messungen weisen jedoch auf veränderte Phasenanteile der fcc und hcp Phase innerhalb der Drähte hin, da die effektive Anisotropie erheblich von der für Nanodrähte mit hohem Aspektverhältnis erwarteten Formanisotropie abweicht. Diese Änderung der effektiven Anisotropie ist auf die bevorzugte Ausrichtung der hexagonalen c-Achse des Co-Pt senkrecht zur Drahtachse zurückzuführen. Vielversprechende Template mit deutlich kleineren Dimensionen sind Diblockcopolymertemplate. Es wurden Versuche zur Abscheidung von Co und Co-Pt in diese Template durchgeführt. Als Gründe für die inhomogene Templatfüllung wurden Inhomogenitäten in der Schichtdicke sowie eine gewisse Rauhigkeit der Substrate identifiziert. Aufgrund der ungleichmäßigen Fülleg werden die magnetischen Eigenschaften durch große, halbkugelförmige Abscheidunge auf der Oberfläche des Templates bestimmt. Darüber hinaus wurden aus wenige nm dicken Au/Co/Au Filmen hergestellte Mikroröhren magnetisch charakterisiert. Temperaturabhängige Messungen zeigen ein Exchange Bias Verhalten, das durch beim Abkühlen induzierte Spannungen erklärt wird. Unterschiede im magnetischen Verhalten der untersuchten Proben werden abschließend im Hinblick auf die verschiedenen konkurrierenden magnetischen Anisotropien in verschiedenen Geometrien diskutiert.

The R2PdSi3 (R = heavy rare earth) have been synthesized first in 1990 in the search for materials with unusual electronic properties. The availability of single crystals was the starting point for several investigations of the magneto-crystalline anisotropy, also in applied magnetic fields. The results of the observed properties in resistivity, magnetization and susceptibility lead to the summary that these compounds range from interesting to exotic and that their magnetic properties are low dimensional, spin-glass like and altogether “novel”. The focus of this thesis is the careful analysis of the magnetic properties and magnetic structures of single crystalline R2PdSi3 (R = Gd, Tb, Dy, Ho, Er, Tm). The investigation of macroscopic properties uses magnetization and ac-susceptibility measurements. Resulting from these investigations are magnetic phase diagrams. Neutron and resonant X-ray diffraction measurements elucidate the magnetic structure for the investigated compounds. The phase diagram of Tb2PdSi3 is the starting point of a detailed neutron diffraction study in applied magnetic fields up to 6.5 T and in the temperature range from 0.05 K to 100 K on this compound. Key to the understanding of the R2PdSi3 is the strong coupling of crystallographic structure to the magnetic properties. Thus the established framework of exchange interaction and magneto-crystalline anisotropy allows a collective description instead of a “novel” behavior. / Die R2PdSi3 (R = schwere seltene Erde) sind erstmals 1990, im Rahmen der Suche nach Materialien mit ungewöhnlichen elektronischen Eigenschaften, synthetisiert worden. Die Verfügbarkeit von Einkristallen war der Startpunkt für eine Vielzahl von Untersuchungen, auch in angelegten Magnetfeldern, der magneto-kristallinen Anisotropie. Das Ergebnis der untersuchten Eigenschaften Widerstand, Magnetisierung und Suszeptibilität führte zu dem Schluss, dass diese Verbindungen interessant bis exotisch und das ihre magnetischen Eigenschaften niedrig dimensional, spin-glas ähnlich und insgesamt “neuartig“ sind. Der Schwerpunkt dieser Dissertation ist die genaue Analyse der magnetischen Eigenschaften und Magnetischen Strukturen von einkristallinen R2PdSi3 (R = Gd, Tb, Dy, Ho, Er, Tm). Magnetisierungs- und Suszeptibilitäts-Messungen werden zur Untersuchung der makroskopischen Eigenschaften benutzt. Resultat dieser Untersuchungen sind magnetische Phasendiagramme. Neutronen und resonante Röntgendiffraktrometrie klären die magnetische Struktur der untersuchten Verbindungen auf. Das Phasendiagramm von Tb2PdSi3 ist der Startpunkt einer detaillierten Neutronendiffraktionsuntersuchung dieser Verbindung in Magnetfeldern bis 6.5 T und im Temperaturbereich von 0.05 K und 100 K. Der Schlüssel zum Verständnis der R2PdSi3 ist die starke Kopplung der kristallografischen Struktur und der magnetischen Eigenschaften. Dadurch erlaubt das etablierte System aus Austauschwechselwirkung und magneto-kristalliner Anisotropie eine gemeinsame Beschreibung anstatt „neuartigem“ Verhalten.

Die magnetischen Eigenschaften von Li2CuO2 sind seit mehr als zwei Jahrzehnten Gegenstand theoretischen und experimentellen Interesses. Über die genaue Natur der magnetischen Wechselwirkungen in diesem Isolator konnte jedoch keine Einigkeit erzielt werden. Während das Material von Seiten theoretischer Untersuchungen als quasi-eindimensionaler Magnet mit starken ferromagnetischen Kopplungen entlang der Kette verstanden wurde, legten experimentelle Studien dominierende dreidimensionale Zwischenkettenkopplungen nahe. Im Rahmen dieser Dissertation werden auf der Grundlage von Untersuchungen des magnetischen Anregungsspektrums mittels inelastischer Neutronenstreuung und dessen Analyse innerhalb eines Spinwellenmodels die führenden magnetischen Wechselwirkungen in Li2CuO2 bestimmt. Es wird zweifelsfrei nachgewiesen, dass das Material eine quasi-eindimensionale Spinkettenverbindung darstellt. Insbesondere kann die Konkurrenz von ferro- und antiferromagnetischen Wechselwirkungen entlang der Ketten nachgewiesen werden. Die Anwendbarkeit einer Spinwellenanalyse dieses niedrigdimensionalen Spin-1=2 Systems wird gezeigt. Das magnetische Phasendiagramm wird mittels Messungen von spezifischer Wärme, thermischer Ausdehnung und Magnetostriktion sowie der Magnetisierung in statischen und gepulsten Magnetfeldern untersucht und im Bezug auf die Austauschwechselwirkungen diskutiert. Aufgrund seiner einfachen kristallographischen und magnetischen Struktur stellt Li2CuO2 ein potentiell wertvolles Modellsystem in der Klasse der Spinkettenverbindungen mit konkurrierenden ferro- und antiferromagnetischen Wechselwirkungen dar. / The magnetic properties of Li2CuO2 have attracted interest since more than two decades, both in theory and experiment. Despite these efforts, the precise nature of the magnetic interactions in this insulator remained an issue of controversial debate. From theoretical studies, the compound was understood as a quasi-one-dimensional magnet with strong ferromagnetic interactions along the chain, while in contrast, experimentally studies suggested dominant three-dimensional inter-chain interactions. In this thesis, the leading magnetic exchange interactions of Li2CuO2 are determined on the basis of a detailed inelastic neutron scattering study of the magnetic excitation spectrum, analyzed within spin-wave theory. It is unequivocally shown, that the material represents a quasi-one-dimensional spin-chain compound. In particular, the competition of ferro- and antiferromagnetic interactions in the chain has been evidenced. The applicability of a spin-wave model for analysis of this low-dimensional spin-1=2 system is shown. The magnetic phase diagram of Li2CuO2 is studied by specific heat, thermal expansion and magnetostriction measurements as well as magnetization measurements in both static and pulsed magnetic fifields. The phase diagram is discussed with respect to the exchange interactions. With its simple crystallographic and magnetic structure, Li2CuO2 may serve as a worthwhile model system in the class of spin-chain compounds with competing ferromagnetic and antiferromagnetic interactions.

Das Auftreten von Supraleitung in Systemen mit schweren Fermionen, erstmals entdeckt in CeCu_2Si_2, wird mit der Nähe zu einem quantenkritischen Punkt in Verbindung gebracht. Daraus ergibt sich ein komplexes Zusammenspiel von Magnetismus und Supraleitung, das in der vorliegenden Arbeit durch Messungen der spezifischen Wärme, der Wechselfeldsuszeptibilität und durch inelastische Neutronenstreuexperimente an verschiedenen Einkristallen von CeCu_2(Si_{1-x}Ge_x)_2 untersucht wird. Der Schwerpunkt liegt auf der genauen Charakterisierung des magnetischen Anregungsspektrums von CeCu_2Si_2 des S-Typs. Die Ergebnisse der Neutronenstreumessungen implizieren stark, dass die Kopplung der supraleitenden Cooper-Paare durch überdämpfte Spinfluktuationen vermittelt wird, die in der Umgebung eines Quantenphasenübergangs gehäuft auftreten. Unter Substitution einiger Si- durch Ge-Atome in CeCu_2Si_2 stabilisiert sich die magnetische Ordnung, und die Supraleitung wird zunehmend unterdrückt. Neutronenstreumessungen ergeben, dass dies bei 2 % Ge-Substitution dazu führt, dass sich Magnetismus und Supraleitung gegenseitig verdrängen, während sie bei 10 % Ge-Substitution mikroskopisch koexistieren. - (Die Dissertation ist veröffentlicht im Logos Verlag Berlin GmbH, Berlin, Deutschland, http://www.logos-verlag.de, ISBN: 978-3-8325-2456-2) / The occurrence of superconductivity in systems with heavy fermions, discovered for the first time in CeCu_2Si_2, is often linked to the vicinity of a quantum critical point. This results in a complex interplay of magnetism and superconductivity, which is studied by means of specific heat and ac susceptibility measurements as well as neutron scattering experiments on different single crystals of CeCu_2(Si_{1-x}Ge_x)_2 in the present thesis. The focus is put on the detailed characterisation of the magnetic excitation spectrum in S-type CeCu_2Si_2. Neutron scattering results strongly imply that the coupling of superconducting Cooper pairs is mediated by overdamped spin fluctuations, which accumulate in the vicinity of a quantum phase transition. By substituting Si by Ge atoms in CeCu_2Si_2 magnetic order is stabilised and superconductivity successively suppressed. Neutron scattering experiments demonstrate that 2 % Ge substitution leads to magnetic order being displaced by superconductivity on decreasing temperature, whereas both coexist microscopically in the case of 10 % Ge substitution.

The structure and magnetism of selected compounds of the pnictides iron based superconductors with chemical formula LnO{1-x}FeAsFx (Ln = La,Sm and Ce), commonly known as 1111, and of rare earth iron borates RFe3(BO3)4 (R = Tb, Gd, Nd and Y), were studied by means of hard x-ray diffraction. For the 1111 pnictides compounds, Rietveld refinement of powder x-ray diffraction measurements at room temperature reveals, that the ionic substitution of O by F has no effect on the structure of the FeAs layers of tetrahedra, whereas the major changes takes place in the LnO layer. These changes are reflected as a shrinkage of the crystal lattice, specially in the c direction. Additionally, a study of the temperature dependent structure of the Sm and Ce-1111 compounds was performed and an estimation of the the structural transition temperature was obtained. The results of the structural measurements, combined with electrical resistivity and µSR, were used to construct the Sm and Ce-1111 phase diagrams. These phase diagrams are characterized by two regions, consisting of a spin density wave (SDW) state and a superconducting state, which are sharply separated upon doping. Considering the different Ln ion, upon F doping the transition temperatures are more efficiently suppressed in Ce-1111 as compared to Sm-1111. More intriguingly, for the Ce case, a coexistence region between static magnetism and superconductivity without an orthorhombic distortion has been observed. Further analysis of the width of the Bragg peaks reveals strong lattice fluctuations towards phase transitions, which are reflected in magnetic and transport properties. Moreover, a strong damping of the lattice fluctuations is observed at Tc for superconducting Sm-1111 samples, giving experimental evidence of competing orders towards phase transitions in the iron pnictides. Regarding the iron borates, non-resonant x-ray scattering studies have shown several new diffraction features, from the appearance of additional reflections that violate the reflection conditions for the low temperature crystal structure, to the emerging of commensurate superlattice peaks that appear below TN. A detailed analysis of the structure factors and q dependencies of the earlier reflections, demonstrate their magnetic nature. Additional resonant x-ray magnetic scattering experiments on NdFe3(BO3)4 were performed at the Nd L2,3 and Fe K edges. The results show that the magnetization behavior is different for the Nd and for the Fe sublattices. Moreover, we find that the magnetization of the Nd sublattice is induced by the Fe magnetization. The temperature dependent measurements also show a commensurate to incommensurate transition where the magnetic structure changes from a commensurate collinear structure, where both Nd and Fe moments align in the hexagonal basal plane, to an incommensurate spin helix structure that propagates along c. When a magnetic field is applied, the spin helix is destroyed and a collinear structure is formed where the moments align in a direction perpendicular to the applied magnetic field. Moreover, the critical field at which the spin helix is destroyed is the same field at which the magnetic induced electric polarization is maximum, thus, showing that the spin helix is not at the origin of the electric polarization.

This dissertation presents the investigation of magnetic exchange and anisotropy in novel metal-organic complexes containing minimum number of magnetic ions. Such complexes can serve as a model system to understand the exciting magnetic phenomena in such class of materials and also can put forward as candidates for the so called molecular nanomagnets. A direct assessment of the effective magnetic moment and the effective interaction between the metal ions in the complex can be done using magnetization measurements. Here the magnetization studies are performed as a function of temperature and field using a SQUID magnetometer. Yet another powerful tool to characterize and determine the spin levels, the ESR spectroscopic methods, has also been exploited. The study of the dynamical properties of this class of materials was relevant to understand the relaxation mechanism in the low temperatures. For this a new ac susceptometer has been built in house which was another main objective of this dissertation work. The design, fabrication, calibration and automation done on this device is presented in this thesis. The device has been tested using the known molecular magnet Mn12 acetate, and the antiferromagnet Dy2PdSi3. The present work is mainly focused on the magnetic properties of Mn, Ni and Fe based organometallic complexes. The studied Mn dimer with different acceptor and donor ligands exhibit the fine tuning of the electron density at the core of molecular complex by variation in ligands. This in turn shows that the change in peripheral ligands can control the magnetism of the molecule. The influence of the change in Ni-S-Ni bond angle in the magnetic exchange interaction is studied in a Ni(2) dimer and a Ni(2) trimer complex. The Ni dimer complex shows a ferromagnetic interaction (J = -42K) whereas trimer shows an antiferromagnetic interaction (J = 140K). Another Ni based complex bridged via phosphorous has been studied which shows the existence of glassy nature at low temperature. Also a polymeric chain compound based on Fe is studied and presented. All these phosphorous or sulphur bridged complexes are novel materials and these are the first data on these complexes.

Iron filled carbon nanotubes (FeCNT) can be described as carbon nanotubes which contain an iron nanowire of several micrometers length and a diameter of approximately 10-100 nm. The carbon shells protect the iron core from oxidation and mechanical damage thus enabling a wide range of applications that require a long-term stability. The magnetic properties of the enclosed nanowire are in part determined by its small size and elongated shape. Magnetic force microscopy (MFM) measurements show that the iron wire exhibits a single domain behavior. Due to the large shape anisotropy it is magnetized along the long wire axis in the remanent state. Two magnetic monopoles of opposing polarity are located at the wire extremities. Depending on the structure and geometry of the individual nanowire, switching fields in the range of 100-400 mT can be found when the external field is applied along the FeCNT’s easy axis. Cantilever magnetometry shows that the switching can be attributed to a thermally assisted magnetization reversal mechanism with the nucleation and propagation of a domain wall. The defined magnetic properties of individual FeCNT combined with their mechanical strength make them ideal candidates for an application as high resolution high stability MFM probes. The fabrication of such probes can be achieved with the help of a micromanipulation setup in a scanning electron microscope. FeCNT MFM probes achieve a sub 25 nm lateral magnetic resolution. MFM measurements with FeCNT MFM probes in external fields show that the magnetization of these probes is exceptionally stable compared to conventional coated MFM probes. This greatly simplifies the data evaluation of such applied field MFM measurements. The emphasis of this work was put on the calibration of FeCNT probes to enable straightforward quantitative MFM measurements. The defined shape of the magnetically active iron nanowire allows an application of a point monopole description. Microscale parallel current carrying lines that produce a defined magnetic field are used as calibration structures to determine the effective magnetic moment of different MFM probes. The line geometry is varied in order to produce multiple magnetic field decay lengths and investigate the influence on the effective probe moment. The results show that while the effective magnetic monopole moment of a conventional MFM probe increases with an increasing sample stray field decay length, the effective moment of a FeCNT MFM probe remains constant. This enables a MFM probe calibration that stays valid for a large variety of magnetic samples. Furthermore, the fitted monopole moment of a FeCNT probe (in the order of 10E-9 Am) is consistent with the moment calculated from the nanowire geometry and the saturation magnetization of iron.