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Instrumente & Einrichtungen

Probenpräparation

Eine gute Probenpräparation ist die Basis zur grundlegenden Erforschung elektronischer und magnetischer Eigenschaften in polykristallinen Materialien, Einkristallen, dünnen Schichten und Nanopartikeln.

Präparation von Bulkmaterial:

  • Herstellung von polykristallinen Keramiken durch Oberflächenreaktionen (mixed oxide)
  • Herstellung von metallischen Legierungen im Schwebeschmelzverfahren
  • Herstellung von oxidischen und metallischen Einkristallen nach dem Zonenzüchtungs- und Czochralski-Verfahren, sowie über Lösungszüchtung

Ansprechpartner: Jörg Persson

 

Probenpraeparation.jpg

 

Präparation von dünnen Schichten:

Für die Herstellung von dünnen Filmen stehen zwei Hochdruck-Sputteranlagen und zwei Oxid-Molekular-Strahl-Epitaxie (MBE) Anlagen zur Verfügung, wobei eine der Oxid-MBEs in Garching am FRM II als user facility eingerichtet ist. In den Hochdruck Sputteranlagen wird das Material, welches als Film zu wachen ist, als fertiges Target in der passenden Stöchiometrie eingebaut und mit einem Gasgemisch aus Sauerstoff und Argon auf das Substrat gesputtert. Im Gegensatz hierzu wird in den Oxid-MBE Anlagen die gewünschte Stöchiometrie durch die Raten der einzelnen Elementarquellen eingestellt.  Zur in-situ Charakterisierung stehen RHEED (Refraktive High Energie Electron Diffration), LEED (Low Energie Electron Diffraction)  und AES (Auger Electron Spectroscopy) zur Verfügung. Am AES können elementaufgelöste Tiefenprofile erstellt werden, in dem gleichzeitig die Schichten punktuell mit einer Argonionenkanone abgetragen werden. Diese Ionenkanone kann auch zur Strukturierung der Proben mit etwa 100µm Auflösung genutzt werden.

Ansprechpartner: Alexander Weber, Sabine Pütter

 

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Durch die direkte Verzahnung von Probenpräparation und -charakterisierung mit Streumethoden und makroskopischen Messmethoden ergeben sich hervorragende Möglichkeiten zur Variation der für die Funktion des jeweiligen Materials entscheidenden Parameter. 

 

Mössbauer spectroscopy

The JCNS-2 Mössbauer spectroscopy laboratory features two spectrometers for the europium-151 and iron-57 resonances. Mössbauer spectral parameters such as the hyperfine field, the quadrupole splitting, the isomer shift, and the Lamb-Mössbauer factor provide a microscopic access to magnetism, local environment and chemistry, and the lattice dynamics for the probed nuclei. A host of relevant information is accessible for:

  • magnetic ordering and phase transitions,
  • coordination and oxidation state of the resonant atoms,
  • diffusive phenomena,
  • slow electronic or magnetic relaxation, ....

and ideally complements results from scattering and magnetometry experiments.

 

The Jülich Mössbauer spectroscopy laboratory is equipped with a closed cycle cryo-oven that operates between 5 and 850 K. Several other setups are in development, such as a high-temperature controlled atmosphere setup, a cooled source setup, and a Peltier cooler driven mini-cryostat.

 

Moesbauer.pngClosed cycle cryo-oven. Inset: Doppler drive with mounted source and magnetic Mössbauer spectrum of FeNCN at 295 K.

 

Ansprechpartner: Raphael Hermann

 

In-House X-Ray Facilities

A series of instruments for the characterisation of samples using diffraction measurements are available in-house. 

A reflectometer from Bruker AXS equipped with two Goebel mirrors before and after the sample allows for the fast characterisation of thin film samples. 

Powder samples can be characterized in transmission geometry with a Huber Imaging Plate Guinier Camera G670 equipped with CuKα- or MoKα-radiation. The accessible temperature range reaches from 10 to 300 K using a closed-cycle cryostat and from 673 to 1773 K using a laser heating module. 

Furthermore, two single crystal diffractometers  are available. A large 4-circle Huber diffractometer with  an Eulerian cradle operates at a standard CuKα source in combination with Goebel mirrors.  An analyser crystal mounted before the scintillation counter warrants the measurement of  highly resolved data. In addition, the beampath can be evacuated, so that an optimal peak-to-background ratio is achieved.  The instrument is thus optimized for high resolution reciprocal space mapping, in particular on thin sections. A closed cycle He-cryostat (Advanced Research Systems) permits investigations in the temperature range from 300 K to 6.5 K.

The second single crystal diffractometer is a Supernova from Agilent Technologies and is equipped with switchable CuKα and MoKα microfocus sources and a CCD area detector for efficient data collection. It is mainly used for the measurement of diffraction intensities of single crystal samples for structure determination.  A  N2 cryostat and a Helijet from Oxford Instruments allow temperature dependent studies in the range from 490-90K and 90-10K, respectively.

 

X-Ray.png


Ansprechpartner: Karen Friese, Ulrich Rücker

 

MPMS, PPMS, CCMS:

JCNS-2 is equipped with two powerful state-of the-art instruments from Quantum Design, i.e. an MPMS-XL SQUID-magnetometer and a Physical Property Measurement System (PPMS). Both serve to characterize samples with respect to the following physical properties as function of both magnetic field and temperature:

  • Magnetization
  • AC susceptibility
  • Torque magnetometry
  • Heat capacity
  • Thermal transport properties
  • Electrical transport properties
  • Hall effect
  • Seebeck coefficient

With the MPMS system one can measure the magnetization (or more precisely the magnetic moment) and the AC susceptibility at various applied magnetic fields between -7 and +7 T and temperatures between 1.9 and 400 K. One can program scans as function of field, temperature or time as automated sequences, e.g. hysteresis loops (see Figure below), ZFC/FC temperature measurements, magnetization relaxation curves, etc. The sensitivity is 10-8 emu. E.g. cobalt ultrathin films with a nominal thickness of 0.5 nm are routinely measurable. The samples should have a size not exceeding roughly 7mmx7mmx7mm and can be bulk crystals, thin films, nanoparticles, etc.

 

MPMS.pngHysteresis loop on FePt nanoparticles measured using the MPMS SQUID magnetometer at T = 5 K.

 

The PPMS system widens the possible methods to measurements of the heat capacity, thermal transport properties, electrical transport properties or the Seebeck coefficient in applied magnetic fields between -9 and  9 T and temperatures between  1.9 and 400 K. Furthermore, the magnetization and AC susceptibility can also be measured using the PPMS system although with a slightly lower sensitivity of ~10-6 emu compared to the MPMS system. In addition, the PPMS can also be used as a torque magnetometer, which provides information about magnetic anisotropies.

A third available system is the closed cycle measurement system (CCMS) built by Cryogenics Ltd (see Figure below). which provides a flexible measurement platform for magnetic fields up to 14 T in a temperature range between 1.6 and 325 K. The following standard options are available:

  • VSM magnetometry
  • AC susceptibility
  • Hall effect
  • Resistivity
  • Thermal conductivity
  • Seebeck coefficient

Additionally, two specialized options are noteworthy: the AC-specific heat option for very small samples with a mass in the order of few µg, and the resonant ultrasound spectroscopy option that is used for the determination of elastic constants and speed of sound. Measurements are usually fully automatized.

 

CCMS.pngThe CCMS measurement platform with 0-14 T magnetic field and 1.6-325 K temperature range. Inset: AC-specific heat option for µg samples.

 

Ansprechpartner: Emmanuel Kentzinger, Oleg Petracic


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