Matthias Hudl

High mechanical Q-factor measurements on silicon bulk samples

Future gravitational wave detectors will be limited by different kinds of noise. Thermal noise from the coatings and the substrate material will be a serious noise contribution within the detection band of these detectors. Cooling and the use of a high mechanical Q-factor material as a substrate material will reduce the thermal noise contribution from the substrates. Silicon is one of the most interesting materials for a third generation cryogenic detector. Due to the fact that the coefficient of thermal expansion vanishes at 18 and 125 K the thermoelastic contribution to the thermal noise will disappear. We present a systematic analysis of the mechanical Q-factor at low temperatures between 5 and 300 K on bulk silicon (100) samples which are boron doped. The thickness of the cylindrical samples is varied between 6, 12, 24, and 75mm with a constant diameter of 3 inches. For the 75mm substrate a comparison between the (100) and the (111) orientation is presented. In order to obtain the mechanical Q-factor a ring-down measurement is performed. Thus, the substrate is excited to resonant vibrations by means of an electrostatic driving plate and the subsequent ring-down is recorded using a Michelson-like interferometer. The substrate itself is suspended as a pendulum by means of a tungsten wire loop. All measurements are carried out in a special cryostat which provides a temperature stability of better than 0.1K between 5 and 300K during the experiment. The influence of the suspension on the measurements is experimentally investigated and discussed. At 5.8K a highest Q-factor of 4.5 ? 108 was achieved for the 14.9 kHz mode of a silicon (100) substrate with a diameter of 3 inches and a thickness of 12 mm.

Magnetocrystalline anisotropy and the magnetocaloric effect in Fe2P

Magnetic and magnetocaloric properties of high-purity, giant magnetocaloric polycrystalline and single-crystalline Fe2P are investigated. Fe2P displays a moderate magnetic entropy change, which spans over 70 K and the presence of strong magnetization anisotropy proves this system is not fully itinerant but displays a mix of itinerant and localized magnetism. The properties of pure Fe2P are compared to those of giant magnetocaloric (Fe,Mn)2(P,A) (where A=As, Ge, Si) compounds helping understand the exceptional characteristics shown by the latter, which are so promising for heat pump and energy conversion applications.

Memory and rejuvenation in a spin glass

The temperature dependence of the magnetisation of a Cu(Mn) spin glass (T-g approximate to 57 K) has been investigated using weak probing magnetic fields (H = 0.5 or 0 Oe) and specific thermal protocols. The behaviour of the zero-field-cooled, thermoremanent and isothermal remanent magnetisation on (re-) cooling the system from a temperature (40K) where the system has been aged is investigated. It is observed that the measured magnetisation is formed by two parts: i) a temperature- and observation time-dependent thermally activated relaxational part governed by the age- and temperature-dependent response function and the (latest) field change made at a lower temperature, superposed on ii) a weakly temperature-dependent frozen-in part. Interestingly we observe that the spin configuration that is imprinted during an elongated halt in the cooling, if it is accompanied by a field-induced magnetisation, also includes a unidirectional excess magnetisation that is recovered on returning to the ageing temperature.

Strongly enhanced magnetic moments in ferromagnetic FeMnP0.5Si0.5

The compound FeMnP(0.5)Si(0.5) has been studied by magnetic measurements, Mossbauer spectroscopy, and electronic structure and total energy calculations. An unexpectedly high magnetic hyperfine fie ...

Magnetic order near 270 K in mineral and synthetic Mn2FeSbO6 ilmenite

The structural and magnetic properties of Mn

Order–disorder induced magnetic structures of FeMnP0.75Si0.25

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The crystal and magnetic structure of the magnetocaloric compound FeMnP0.5Si0.5

FeSbO

Phase diagram, structures and magnetism of the FeMnP1-xSix-system

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Aging experiments in a superspin glass system of Co particles in Mn matrix

single-crystalline mineral and ceramic samples synthesized under thermobaric treatment have been investigated, and compared to theoretical predictions based on first-principles electronic structure calculations. This ilmenite system displays a sharp magnetic transition just below the room temperature related to a ferrimagnetic ordering of the Mn

Investigation of the magnetic phase transition and magnetocaloric properties of the Mn2FeSbO6 ilmenite

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