MTD100: Magnetic Transition Detection Coil
The MTD100 coils are a pair of radially stacked copper coils designed to detect gross changes in the magnetic susceptibility of a sample while it is being strained in a Razorbill Instruments stress or strain cell. Such measurements may be preferred over electrical transport, as they do not need contacts to be attached to the sample.
- Detect magnetic transitions without needing electrical contacts to the sample.
- More reliable measurement then resistivity for determining a normal to superconducting transition
- In some cases, suitable for tracking other types of transition, or for de Haas – van Alphen measurements.
- Ultraminiature size - suitable for detecting transitions on samples with diameters <0.2 mm.
Magnetic Transition Detection
- The MTD100 consists of two coupled inductors. If one is excited with a fixed AC current, a voltage may be measured in the other. When placed adjacent to a sample of material, the susceptibility of that material affects the strength of the coupling.
- Signal also affected by changes in geometry of the coils due to thermal expansion, and by changes in the geometry of the sample due to thermal expansion and applied strain, so should only be used to detect large changes in susceptibility, not absolute values of susceptibility.
- They are also suitable for detecting the frequency of de Haas – van Alphen oscillations in susceptibility, provided that the measurements electronics can recover the signal with sufficient resolution at the required frequency.
- Can be directly bonded to the sample or attached to a thin substrate, such as kapton and then pressed against the sample.
- Designed to be used in combination with the WP100 wiring platform.
- Minature coils designed for small samples.
- Can be used with samples with diameters smaller than the coil diameter with some loss of sensitivity.
Plot of change in output signal at onset of superconductivity against sample size. Based on numerical simulation of a square-section 1 mm long rod adjacent to the flat side of the MTD100 undergoing a change in volume susceptibility Δχ = 1
|Resistance, Transmit Coil||At room temperature
At 4 K
|Inductance, Transmit Coil||7||μH|
|Resistance, Receive Coil||At room temperature
At 4 K
|Inductance, Receive Coil||14||μH|
|Capacitance, Between Coils||12||pF|
|Absolute Maximum Current||20||mARMS|
|At room temperature
At 4 K
|Typical output signal size1||1||mVRMS|
|Typical change in signal at onset of
- At 3 KHz, with 5 mA RMS excitation current
- There are components of the measurement. A clean sinusoidal excitation signal must be generated on the transmit coil, and the induced AC signal must be measured on the receive coil.
- The ideal device to achieve both of these requirements is a lock-in amplifier.
- If the excitation signal generated is a voltage, rather than a current, then a current limiting resistor should be used in series to prevent the current increasing as the resistance of the transmit coil decreases at low temperature.
- If a lock-in amplifier is not available, advanced users could use a wide range of instruments to carry out the measurement, including a capacitance bridge or a PC sound card.
These dimensioned drawings and CAD models will enable you to determine your preferred way to mount the cell in your cryostat.
To download the .STEP files, please right-click on the the download link and select "save link as..." then select where you want to save the file, specifying a .step filetype.