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This thesis investigates the growth of intermetallic compounds by co-sputtering from single elemental targets. The preliminary work involved constructing a sputtering set-up to grow abinary alloy (Sm-Co) and investigating how to control the composition spread that was obtained. Having achieved this, a larger sputtering flange was built up to grow the ternary Heusler alloy, Co₂MnSi. Co₂MnSi has been predicted to be a half-metallic ferromagnet, which means that there is an energy gap in the minority spin band at the Fermi energy. This leads to 100% spin polarised conduction electrons, which would enable ideal spin-device performance to be obtained. Co₂MnSi is particularly promising because it is predicted to have a large energy gap in the minority band of ~0.4 eV and has the highest Curie temperature among the known Heuslers of 985 K. Initially, Co₂MnSi was grown on a-plane sapphire and stoichiometric films were single phase and highly (110) textured, without the use of a seed layer. They exhibited the bulk value of the saturation magnetisation, Ms and films grown at the highest deposition temperature (715 K) showed the lowest resistivity (47 μΩcm at 4.2 K) and the lowest room temperature coercivity (18 Oe). The spin polarisation of the transport current, Pt of a 400 nm film grown at this deposition temperature was 54%, consistent with measurements on bulk single crystals. Ms decreased with decreasing film thickness indicating a graded disorder. By growing on GaAs (001), which has a similar lattice parameter to Co₂MnSi it was expected that this disordered region would be confined to the first few atomic layers. However, this was not the case because interfacial reactions resulted in the formation of an epitaxial Mn-As region, and a thin interfacial layer that was Co-Ga rich. This prevented the lattice matching of the Co₂MnSi to the GaAs(001) hence hindering epitaxial growth of the Heusler. The reaction zone also meant that films exhibited a Ms slightly below the bulk value. The expected fourfold anisotropy was not obtained for this cubic material, which is most likely due to the anisotropy of the reconstructed GaAs surface. Inspite of this anomalous behaviour, Pt was 55%, similar to the result obtained on sapphire, indicating that either Pt is independent of orientation or that the Heusler surface reconstructs in the same way. Films showed some improved properties to films grown on a-plane sapphire, indicating the potential of growing on this technologically important substrate. With this in mind, pseudo spin valves involving Co₂MnSi as one of the ferromagnetic electrodes were fabricated in both the CIP and CPP configurations. Clear low-field spin-valve contributions were observed at 15 K but the MR values are much lower than that expected from a PSV with a predicted 100% spin polarised electrode.

<p> Neutron diffraction techniques have been used to determine the chemical and magnetic order in a single crystal of the Heusler alloy Ni2Mn0.8v0.2sn. This material orders in the Heusler L21 structure and is ferromagnetic. Nuclear Bragg scattering intensity ratios have been measured at 298 K and compared with nuclear structure factor calculations based on a model of the crystal structure. This comparison is used to determine chemical disorder. Magnetic Bragg scattering intensity ratios have been measured at 117 K. These ratios, along with bulk magnetization measurements, are used to determine the spatial distribution of the magnetic moment. The crystal is found to have the L21 structure with possibly 5% or so Ni-Sn disorder. Nearly all of the magnetic moment, which is 3.19 ± .03 μ8/mol, is found to exist on the Mn-V sites. The rest is present on the Sn atoms. The values 3.74 ± .10 μ8/Mn atom and .21 ± .08 μ8/Sn atom result from assuming the V atoms carry no moment. </p> / Thesis / Master of Science (MSc)

In der magnetischen Formgedächtnislegierung Ni-Co-Mn-In kann eine reversible Umwandlung von einer niedrigsymmetrischen, para- oder antiferromagnetischen Phase (Martensit) in eine hochsymmetrische ferromagnetische Phase (Austenit) sowohl durch eine Temperaturerhöhung als auch durch das Anlegen eines Magnetfelds induziert werden. Da dünne Schichten sich als interessantes Modellsystem für magnetische Formgedächtnislegierungen erwiesen haben, wird diese Umwandlung und der mit ihr verbundene inverse magnetokalorische Effekt an epitaktischen Ni-Co-Mn-In-Schichten untersucht. Die Temperatur des Substrats während der Herstellung wird als entscheidender Parameter für die Zusammensetzung und chemische Ordnung der Schicht identifiziert. Untersuchungen der Struktur mittels Röntgenbeugung zeigten, in Übereinstimmung mit dem Konzept des adaptiven Martensits, die Koexistenz von Austenit, moduliertem und nichtmoduliertem Martensit bei Raumtemperatur. Dieses Ergebnis wird durch Gefügeabbildungen untermauert. Die Transformation wird sowohl durch temperaturabhängige Röntgenbeugung als auch durch temperatur- und feldabhängige Magnetisierungsmessungen untersucht. Die berechnete Änderung der magnetischen Entropie ist etwa halb so groß wie in massivem Ni-Co-Mn-In. Schließlich wird bei tiefen Temperaturen eine unidirektionale Austauschkopplung zwischen Restaustenit und Martensit nachgewiesen, die auf einen antiferromagnetischen Martensit schließen lässt. / The magnetic shape memory alloy (MSMA) Ni-Co-Mn-In shows a reversible transformation from a para- or antiferromagnetic low symmetry phase (martensite) into a ferromagnetic phase of high symmetry (austenite). This transformation can either be induced by raising the temperature or applying a magnetic field. Since thin films have be shown to be an interesting model system for MSMAs, this transformation and the associated inverse magnetcaloric effect are investigated in epitaxial Ni-Co-Mn-In films. The temperature of the substrate during deposition is identified as the essential parameter controlling both composition and chemical order. By studying structure using x-ray diffraction (XRD) the coexistence of austenite and modulated (14M) as well as nonmodulated martensite (NM) is shown. Coexistence of NM and 14M is also visible in micrographs of the films surface. This confirms results obtained for epitaxial Ni-Mn-Ga and validates the concept of adaptive martensite in this alloy. The transformation is investigated by temperature-dependent XRD and temperature- and field-dependent magnetometry. A positive change in entropy is calculated which is about half compared to bulk. Finally, an exchange bias between residual austenite and martensite is observed, which suggests an antiferromagnetic order in the martensitic state.

Foram analisados, por difração de raios X, dois materiais policristalinos: uma liga de Heusler (C02ScSn), onde amostras originárias da mesma preparação foram submetidas a vários tratamentos térmicos distintos, e um material biocerâmico. Para o refinamento utilizou-se o Método de Rietveld. Na análise feita com a liga de Heusler (C02ScSn) tornou-se evidente uma segunda fase: C02Sn, e que não foi refinada por não haver um modelo de estrutura para a mesma. Assim, o refinamento foi efetuado, apenas para a estrutura conhecida, escolhendo algumas alternativas de função perfil, tais como as funções Gaussiana, pseudo-Voigt e Thompson¬-Cox-Hastings pseudo-Voigt modificada. A radiação de fundo também foi refinada utilizando o polinômio de quinta ordem. Os resultados obtidos foram equivalentes. Dos resultados obtidos nos refinamentos, conclui-se que as condições de preparação das amostras Fl17 (proveniente da amostra original, tratada a 600°C por 60 horas, em seguida moída, tratada a 200°C por 80 horas e submetida a resfriamento lento) e Al17 (proveniente da amostra original, tratada a 800°C por 48 horas e submetida a resfriamento lento), foram as mais satisfatórias. As amostras Fl17 e Al17 foram mais satisfatórias, respectivamente, segundo os índices de discordância do refinamento: qualidade do refinamento, de perfil e de perfil ponderado, e segundo os índices de discordância do refinamento: de Bragg e de fator de estrutura. Pela análise feita com o material biocerâmico tornou-se evidente a presença de duas fases cristalinas: hidroxiapatita [Ca10 (PO4) 6 (OH)2] e whitlockite [&#946;Ca3(PO4)2], e com o refinamento foi possível calcular a composição da mistura nas amostras. Pode-se concluir que o processo utilizado na obtenção da amostra HAIII103 ([Jarcho, M., Bolen, H. C., Thomas, M. B., Bobick, J., Kay, J. F. and Doremus, R. H., 1976. J. Matter. Sci., 11, 2027-2035], e homogeneizada com a mistura de colágeno: polímeros hidrofílicos) mostrou-se mais adequado, já que a mesma apresentou-se mais rica em hidroxiapatita. / Two polycrystalline materials were analysed by X-ray diffraction: a Heusler alloy (Co2ScSn), where samples originating from the same preparation were submitted to several different thermal treatments, and a bioceramic material. The Rietveld method was employed for the refinement. The analysis of the Heusler alloy clearly revealed the presence of a second phase: CO2Sn, which was not refined due to the absence of a structural model. Thus, the refinement was performed, only for the component with known structural model, choosing several alternative profile functions such as Gaussian, pseudo-Voigt and Thompson-Cox-Hastings modified pseudo-Voigt. The background radiation also was refined using a fifth order polynomial. The results obtained were equivalent. From the results obtained by the refinement it can be concluded that the preparation conditions of sample Fl17 (arising from the original sample treated at 600OC for 60 hours, ground, treated at 200OC for 80 hours and annealed) and Al17 (arising from the original sample treated at 800OC for 48 hours and annealed) were more satisfactory. The samples F117 and Al17 were more satisfactory, respectivelly, according to the disagreement factors goodness of fit, pattern and weighted pattern, and according to the disagreement factors Bragg and structure factor. The analysis of the bioceramic material clearly revealed the presence of two crystalline phases: hydroxyapatite [Ca10(PO4)6(OH)2] and whitlockite [&#946;-Ca3(PO4)2] and via the refinement it was possible to calculate its composition. The procedure used to obtain sample HAIII103 ([Jarcho, M., Bolen, H. C., Thomas, M. B., Bobick, J., Kay, J. F. and Doremus, R. H., 1976. J. Matter. Sci., 11, 2027-2035], and homogeneized with a mixture of collagenous: hidrophylic polymers) proved to be the most adequate since this sample was richer in hydroxyapatite.

Foram analisados, por difração de raios X, dois materiais policristalinos: uma liga de Heusler (C02ScSn), onde amostras originárias da mesma preparação foram submetidas a vários tratamentos térmicos distintos, e um material biocerâmico. Para o refinamento utilizou-se o Método de Rietveld. Na análise feita com a liga de Heusler (C02ScSn) tornou-se evidente uma segunda fase: C02Sn, e que não foi refinada por não haver um modelo de estrutura para a mesma. Assim, o refinamento foi efetuado, apenas para a estrutura conhecida, escolhendo algumas alternativas de função perfil, tais como as funções Gaussiana, pseudo-Voigt e Thompson¬-Cox-Hastings pseudo-Voigt modificada. A radiação de fundo também foi refinada utilizando o polinômio de quinta ordem. Os resultados obtidos foram equivalentes. Dos resultados obtidos nos refinamentos, conclui-se que as condições de preparação das amostras Fl17 (proveniente da amostra original, tratada a 600°C por 60 horas, em seguida moída, tratada a 200°C por 80 horas e submetida a resfriamento lento) e Al17 (proveniente da amostra original, tratada a 800°C por 48 horas e submetida a resfriamento lento), foram as mais satisfatórias. As amostras Fl17 e Al17 foram mais satisfatórias, respectivamente, segundo os índices de discordância do refinamento: qualidade do refinamento, de perfil e de perfil ponderado, e segundo os índices de discordância do refinamento: de Bragg e de fator de estrutura. Pela análise feita com o material biocerâmico tornou-se evidente a presença de duas fases cristalinas: hidroxiapatita [Ca10 (PO4) 6 (OH)2] e whitlockite [&#946;Ca3(PO4)2], e com o refinamento foi possível calcular a composição da mistura nas amostras. Pode-se concluir que o processo utilizado na obtenção da amostra HAIII103 ([Jarcho, M., Bolen, H. C., Thomas, M. B., Bobick, J., Kay, J. F. and Doremus, R. H., 1976. J. Matter. Sci., 11, 2027-2035], e homogeneizada com a mistura de colágeno: polímeros hidrofílicos) mostrou-se mais adequado, já que a mesma apresentou-se mais rica em hidroxiapatita. / Two polycrystalline materials were analysed by X-ray diffraction: a Heusler alloy (Co2ScSn), where samples originating from the same preparation were submitted to several different thermal treatments, and a bioceramic material. The Rietveld method was employed for the refinement. The analysis of the Heusler alloy clearly revealed the presence of a second phase: CO2Sn, which was not refined due to the absence of a structural model. Thus, the refinement was performed, only for the component with known structural model, choosing several alternative profile functions such as Gaussian, pseudo-Voigt and Thompson-Cox-Hastings modified pseudo-Voigt. The background radiation also was refined using a fifth order polynomial. The results obtained were equivalent. From the results obtained by the refinement it can be concluded that the preparation conditions of sample Fl17 (arising from the original sample treated at 600OC for 60 hours, ground, treated at 200OC for 80 hours and annealed) and Al17 (arising from the original sample treated at 800OC for 48 hours and annealed) were more satisfactory. The samples F117 and Al17 were more satisfactory, respectivelly, according to the disagreement factors goodness of fit, pattern and weighted pattern, and according to the disagreement factors Bragg and structure factor. The analysis of the bioceramic material clearly revealed the presence of two crystalline phases: hydroxyapatite [Ca10(PO4)6(OH)2] and whitlockite [&#946;-Ca3(PO4)2] and via the refinement it was possible to calculate its composition. The procedure used to obtain sample HAIII103 ([Jarcho, M., Bolen, H. C., Thomas, M. B., Bobick, J., Kay, J. F. and Doremus, R. H., 1976. J. Matter. Sci., 11, 2027-2035], and homogeneized with a mixture of collagenous: hidrophylic polymers) proved to be the most adequate since this sample was richer in hydroxyapatite.

Submitted by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2018-06-20T14:23:09Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Paola- Dissertacao.pdf: 1239637 bytes, checksum: 85c1de7a05b461f7f506a5ad3652d878 (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2018-06-20T14:23:25Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Paola- Dissertacao.pdf: 1239637 bytes, checksum: 85c1de7a05b461f7f506a5ad3652d878 (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2018-06-20T14:23:37Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Paola- Dissertacao.pdf: 1239637 bytes, checksum: 85c1de7a05b461f7f506a5ad3652d878 (MD5) / Made available in DSpace on 2018-06-20T14:23:37Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Paola- Dissertacao.pdf: 1239637 bytes, checksum: 85c1de7a05b461f7f506a5ad3652d878 (MD5) Previous issue date: 2018-05-18 / The study of the Half-Heusler alloy has drawn a lot of attention among the researchers due to their characteristics and applications, in general, to characterize as ferromagnetic alloys, constituted by non-magnetic elements. In this research, the TiNiSn alloy was produced by the Mechanical Alloyng in two routes, the first in 3h with analysis done at each hour, and the second at 4h straight. The structure and its thermal behavior were investigated by the following techniques: X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), Thermal Treatment (TT) and Rietveld refinement. According to results obtained, respectively, it was seen that the TiNiSn alloy was produced in 4h grinding by the mechanical alloying method, its diffractograms were verified in order to discover the phases formed in the synthesized alloy in 4h, and by the analysis of differential calorimetry of scanning was seen the thermal behavior of the sample at varied temperatures in a temperature range of 30 °C and 500 °C, so it was possible to analyze the sample by the Thermal Treatment technique. / O estudo da liga Half-Heusler tem chamado muita atenção entres os pesquisadores devido as suas características e aplicações, de uma maneira geral, por caracterizarem-se como ligas ferromagnéticas, constituídas por elementos não magnéticos. Neste trabalho foi produzida e a liga TiNiSn, do tipo Half-Heusler, a fim de analisar sua estrutura. Nesta pesquisa, a liga TiNiSn foi produzida pela técnica de Moagem Mecânica de Alta Energia em dois tempos de moagem, a primeira em 3h com análise feita a cada uma hora, e a segunda em 4h sem pausas. A estrutura e seu comportamento térmico foram investigados pelas seguintes técnicas: Difração de raios X (DRX), Calorimetria Diferencial de Varredura (DSC), Tratamento Térmico (TT) e método de refinamento estrutural de Rietveld (MR). De acordo com os resultados obtidos, respectivamente, foi visto que a liga TiNiSn foi produzida em 4 h de moagem pelo método de mechanical alloying, seus difratogramas foram verificados afim de descobrir as fases formadas na liga sintetizada em 4 h, e pela análise de calorimetria diferencial de varredura (DSC) foi visto o comportamento térmico da amostra em temperaturas variadas, em uma faixa de 30 °C à 500 °C, subsequentemente, foi possível analisar a amostra pela técnica de tratamento térmico.

Um den ständig steigenden Energiebedarf durch Kälteanlagen wie Kühlschränke oder Klimaanlagen zu verringern, sind in den vergangenen Jahren Kühlprozesse in den Mittelpunkt aktueller Forschungen gerückt, die auf Phasenumwandlungen in Festkörpern beruhen. Ein Beispiel dafür sind magnetokalorische Materialien, zu denen auch das in der vorliegenden Arbeit untersuchte Ni-Mn-Ga-Co gehört. In dieser Heusler-Legierung tritt eine Phasenumwandlung erster Ordnung von einer ferromagnetischen, kubischen Hochtemperaturphase (Austenit) in eine tetragonal verzerrte Tieftemperaturphase (Martensit) mit geringerer Magnetisierung auf. Der Unterschied in den Magnetisierungen beider Phasen erlaubt es auch, diese Phasenumwandlung durch ein Magnetfeld zu induzieren. Hierbei kühlt sich das Material durch eine Verringerung der Gitterentropie in dem System ab. Ein Nachteil von Phasenumwandlungen erster Ordnung ist die damit verbundene Hysterese. Außerdem lässt sich der magnetokalorische Effekt durch die scharfe Umwandlung nur in einem kleinen Temperaturbereich effektiv nutzen. Das Ziel dieser Arbeit besteht darin, anhand epitaktisch gewachsener Ni-Mn-Ga-Co-Schichten auf PMN-PT-Substraten zu untersuchen, ob und wie die Umwandlungstemperatur und damit auch die Hysterese der Heusler-Legierung durch mechanische Spannung beeinflusst werden kann. Dafür soll durch Anlegen eines elektrischen Feldes an das piezoelektrische Substrat die Ni-Mn-Ga-Co-Schicht reversibel mechanisch verspannt und die daraus resultierenden Veränderungen der strukturellen und magnetischen Eigenschaften untersucht werden. Im ersten Ergebnisteil wird zunächst gezeigt, dass epitaktische Ni-Mn-Ga-Co-Schichten auf PMN-PT wachsen können und diese einen strukturellen und magnetischen Phasenübergang zeigen. Eine Beeinflussung der bei Raumtemperatur vorliegenden Phase ist dabei über eine Variation der chemischen Zusammensetzung der Probe möglich. Im Anschluss werden die Auswirkungen eines angelegten elektrischen Feldes auf die strukturellen und magnetischen Eigenschaften analysiert. Röntgenuntersuchungen zeigen, dass die piezoelektrische Dehnung des Substrats vollständig auf das Ni-Mn-Ga-Co übertragen werden kann. Allerdings treten bei hohen Temperaturen aufgrund einer Phasenumwandlung im PMN-PT nichtlineare Dehnungseffekte auf. Eine Veränderung der Umwandlungstemperaturen durch die Dehnung des Ni-Mn-Ga-Co ist jedoch nicht möglich. Als wahrscheinliche Ursache dafür wird eine Besonderheit des martensitischen Gefüges der Ni-Mn-Ga-Co-Schichten diskutiert. Im Austenit wurde jedoch eine vollständig reversible Änderung der Magnetisierung um bis zu 7 % gemessen. Diese Magnetisierungsänderung bietet einen interessanten Anknüpfungspunkt für weitergehende Untersuchungen dieses Systems für multikalorische Anwendungen.

New magnetocaloric Heusler alloys with larger magnetocaloric effects need to function in relatively low applied magnetic fields ≤ 1 T. Therefore, the emphasis of this Ph.D. thesis was to understand how the first order magnetostructural transformation in Mn-rich Ni-based rare-earth free magnetocaloric Heusler alloys works and to use this understanding for the design of new Mn-rich Ni-based rare-earth free magnetocaloric Heusler alloys. In this context, the rare-earth free, non-toxic, and environmentally friendly Heusler series: Ni2−xMn1+xSn, Mn50Ni50−ySny, and Ni-(Co-)Mn-In were systematically studied. In detail, it pointed out that in the Heusler series Ni2−xMn1+xSn, the structure and the disorder character can be predicted by using simple rules. On the other hand, an isoplethal section of the Heusler series Mn50Ni50−ySny was derived, which is very useful for the design of new magnetocaloric materials. In addition to it, in the Heusler alloy Ni49.9Mn34.5In15.6 a large saturated magnetic moment and a reversible magnetocaloric effect at its purely second order magnetic phase transition was present, which is in reasonable agreement with ab initio calculations. Finally, the effect of post-annealing on the Heusler alloy Ni45.2Co5.1Mn36.7In13 revealed that the magnetocaloric effect could be tuned and improved significantly. Consequently, this work shows that the Heusler alloys are promising candidates for magnetocaloric applications.

In der magnetischen Formgedächtnislegierung Ni-Co-Mn-In kann eine reversible Umwandlung von einer niedrigsymmetrischen, para- oder antiferromagnetischen Phase (Martensit) in eine hochsymmetrische ferromagnetische Phase (Austenit) sowohl durch eine Temperaturerhöhung als auch durch das Anlegen eines Magnetfelds induziert werden. Da dünne Schichten sich als interessantes Modellsystem für magnetische Formgedächtnislegierungen erwiesen haben, wird diese Umwandlung und der mit ihr verbundene inverse magnetokalorische Effekt an epitaktischen Ni-Co-Mn-In-Schichten untersucht. Die Temperatur des Substrats während der Herstellung wird als entscheidender Parameter für die Zusammensetzung und chemische Ordnung der Schicht identifiziert. Untersuchungen der Struktur mittels Röntgenbeugung zeigten, in Übereinstimmung mit dem Konzept des adaptiven Martensits, die Koexistenz von Austenit, moduliertem und nichtmoduliertem Martensit bei Raumtemperatur. Dieses Ergebnis wird durch Gefügeabbildungen untermauert. Die Transformation wird sowohl durch temperaturabhängige Röntgenbeugung als auch durch temperatur- und feldabhängige Magnetisierungsmessungen untersucht. Die berechnete Änderung der magnetischen Entropie ist etwa halb so groß wie in massivem Ni-Co-Mn-In. Schließlich wird bei tiefen Temperaturen eine unidirektionale Austauschkopplung zwischen Restaustenit und Martensit nachgewiesen, die auf einen antiferromagnetischen Martensit schließen lässt.:1 Einleitung 6 2 Grundlagen 8 2.1 Die Martensitische Umwandlung 8 2.2 Der (inverse) magnetokalorische Effekt 9 2.3 Struktur epitaktischer Heusler-Schichten 11 2.3.1 Begriff der Heteroepitaxie 11 2.3.2 Die Heusler-Struktur 12 2.3.3 Martensitische Phasen und Konzept des adaptiven Martensits 12 2.3.4 Orientierung der martensitischen Varianten in epitaktischen Schichten 15 2.4 Einfluss von Zusammensetzung und Ordnung 15 2.5 Magnetische Eigenschaften von Ni-Co-Mn-In 17 2.5.1 Metamagnetische Transformationen in massivem Ni-Co-Mn-In 17 2.5.2 Magnetische Eigenschaften des Austenits und des Martensits 18 2.6 Der Exchange-Bias-Effekt 19 3 Experimentelle Methoden 20 3.1 Schichtherstellung 20 3.1.1 Schichtarchitektur 20 3.1.2 DC-Magnetronsputterdeposition 20 3.2 Bestimmung der Zusammensetzung durch EDX 23 3.3 Einstellung der Schichtdicke 23 3.3.1 Schwingquarz-Ratenmonitor 24 3.3.2 Energieabhängigkeit der charakteristischen Röntgenstrahlung 24 3.4 Strukturbestimmung durch Röntgenbeugung an dünnen Schichten 24 3.4.1 Beugungsbedingung 24 3.4.2 Bragg-Brentano-Geometrie 25 3.4.3 Überstrukturreflexe und chemische Ordnung 25 3.4.4 Vier-Kreis-Geometrie 26 3.5 Gefügeabbildungen 27 3.5.1 Rasterelektronenmikroskopie 27 3.5.2 Rasterkraftmikroskopie 27 3.6 Magnetisierungsmessungen im Vibrationsmagnetometer 28 4 Ergebnisse 29 4.1 Einstellen der Schichtzusammensetzung 29 4.2 Struktur aktiver Schichten 33 4.2.1 Kristallisation und Einstellung chemischer Ordnung 34 4.2.2 Martensitische Struktur 38 4.2.3 In-situ-Untersuchung der strukturellen Umwandlung 43 4.2.4 Nachweis epitaktischen Wachstums 46 4.3 Magnetische Eigenschaften 48 4.3.1 Konsequenzen der strukturellen Umwandlung für die magnetischen Eigenschaften 48 4.3.2 Einfluß der Depositionstemperatur und der Zusammensetzung auf die Umwandlung 50 4.3.3 Magnetfeldinduzierter Austenit 52 4.3.4 Entropieänderung und magnetokalorische Eigenschaften 53 4.3.5 Antiferromagnetismus im Martensit 54 4.4 Schichtmorphologie und martensitisches Gefüge 58 5 Zusammenfassende Diskussion 62 5.1 Einstellung vom Zusammensetzung und chemischer Ordnung 62 5.2 Größe der Hysterese und des Transformationsbereichs 64 5.3 Magnetisch induzierte Übergange und magnetokalorischer Effekt 65 5.4 Magnetische Ordnung im Martensit 66 5.5 Struktur und Gefüge des Martensits 67 5.6 Fazit 68 Literaturverzeichnis 69 / The magnetic shape memory alloy (MSMA) Ni-Co-Mn-In shows a reversible transformation from a para- or antiferromagnetic low symmetry phase (martensite) into a ferromagnetic phase of high symmetry (austenite). This transformation can either be induced by raising the temperature or applying a magnetic field. Since thin films have be shown to be an interesting model system for MSMAs, this transformation and the associated inverse magnetcaloric effect are investigated in epitaxial Ni-Co-Mn-In films. The temperature of the substrate during deposition is identified as the essential parameter controlling both composition and chemical order. By studying structure using x-ray diffraction (XRD) the coexistence of austenite and modulated (14M) as well as nonmodulated martensite (NM) is shown. Coexistence of NM and 14M is also visible in micrographs of the films surface. This confirms results obtained for epitaxial Ni-Mn-Ga and validates the concept of adaptive martensite in this alloy. The transformation is investigated by temperature-dependent XRD and temperature- and field-dependent magnetometry. A positive change in entropy is calculated which is about half compared to bulk. Finally, an exchange bias between residual austenite and martensite is observed, which suggests an antiferromagnetic order in the martensitic state.:1 Einleitung 6 2 Grundlagen 8 2.1 Die Martensitische Umwandlung 8 2.2 Der (inverse) magnetokalorische Effekt 9 2.3 Struktur epitaktischer Heusler-Schichten 11 2.3.1 Begriff der Heteroepitaxie 11 2.3.2 Die Heusler-Struktur 12 2.3.3 Martensitische Phasen und Konzept des adaptiven Martensits 12 2.3.4 Orientierung der martensitischen Varianten in epitaktischen Schichten 15 2.4 Einfluss von Zusammensetzung und Ordnung 15 2.5 Magnetische Eigenschaften von Ni-Co-Mn-In 17 2.5.1 Metamagnetische Transformationen in massivem Ni-Co-Mn-In 17 2.5.2 Magnetische Eigenschaften des Austenits und des Martensits 18 2.6 Der Exchange-Bias-Effekt 19 3 Experimentelle Methoden 20 3.1 Schichtherstellung 20 3.1.1 Schichtarchitektur 20 3.1.2 DC-Magnetronsputterdeposition 20 3.2 Bestimmung der Zusammensetzung durch EDX 23 3.3 Einstellung der Schichtdicke 23 3.3.1 Schwingquarz-Ratenmonitor 24 3.3.2 Energieabhängigkeit der charakteristischen Röntgenstrahlung 24 3.4 Strukturbestimmung durch Röntgenbeugung an dünnen Schichten 24 3.4.1 Beugungsbedingung 24 3.4.2 Bragg-Brentano-Geometrie 25 3.4.3 Überstrukturreflexe und chemische Ordnung 25 3.4.4 Vier-Kreis-Geometrie 26 3.5 Gefügeabbildungen 27 3.5.1 Rasterelektronenmikroskopie 27 3.5.2 Rasterkraftmikroskopie 27 3.6 Magnetisierungsmessungen im Vibrationsmagnetometer 28 4 Ergebnisse 29 4.1 Einstellen der Schichtzusammensetzung 29 4.2 Struktur aktiver Schichten 33 4.2.1 Kristallisation und Einstellung chemischer Ordnung 34 4.2.2 Martensitische Struktur 38 4.2.3 In-situ-Untersuchung der strukturellen Umwandlung 43 4.2.4 Nachweis epitaktischen Wachstums 46 4.3 Magnetische Eigenschaften 48 4.3.1 Konsequenzen der strukturellen Umwandlung für die magnetischen Eigenschaften 48 4.3.2 Einfluß der Depositionstemperatur und der Zusammensetzung auf die Umwandlung 50 4.3.3 Magnetfeldinduzierter Austenit 52 4.3.4 Entropieänderung und magnetokalorische Eigenschaften 53 4.3.5 Antiferromagnetismus im Martensit 54 4.4 Schichtmorphologie und martensitisches Gefüge 58 5 Zusammenfassende Diskussion 62 5.1 Einstellung vom Zusammensetzung und chemischer Ordnung 62 5.2 Größe der Hysterese und des Transformationsbereichs 64 5.3 Magnetisch induzierte Übergange und magnetokalorischer Effekt 65 5.4 Magnetische Ordnung im Martensit 66 5.5 Struktur und Gefüge des Martensits 67 5.6 Fazit 68 Literaturverzeichnis 69