LTD12, Paris
Microstructured magnetic calorimeter
with meander shaped pickup coil
A. Burck
S. Kempf, S. Schäfer,
H. Rotzinger, M. Rodrigues,
T. Wolf, A. Fleischmann,
L. Gastaldo, C. Enss
Kirchhoff-Institute for physicsUniversity Heidelberg
LTD12, Paris
weak thermal link
Metallic magnetic calorimeter
sensor: Au:Er (~100-1000 ppm)
x-ray
dc-SQUID magnetometer
Wärmebad
paramagnetic sensor
absorber
B
thermal bath
LTD12, Paris
cylindrical sensor
circular SQUID-loop
external magnetic field
planar sensor
meander shaped pickup loop
with transformer coupling
Sensor readout schemes
LTD12, Paris
Why meander shaped pickup coils ?
• natural 2d geometry with high filling factor
• no external field coil needed
• bias field is multipole field of high order:
• magnetic detektor response has multipole character
• reduced magn. cross talk between pixel
• reduced pickup of magnetic Johnson noise
• field decays exponentially with distance allows for superconducting absorbers
LTD12, Paris
Characterisation: Prototype-detector
setup:
• large area detector, Asensor= 1mm•1mm
• sputter deposited sensor, Au:Er 750 ppm,
natural isotope mixture ( 22.9 % 167Er)
• Csens 0.4 nJ/K
• expected ΔEFWHM ~ 25eV
• no absorber
3.5 mm
LTD12, Paris
Magnetization
magnetization of the sputter deposited Au:Er shows bulk-properties for temperatures in the range between 2 K-300 K promising result
LTD12, Paris
Magnetization
theory
Au:Er-sensor can reliably be microstructured
magnetization of the sputter deposited Au:Er shows bulk-properties for temperatures down to 45 mK
deviation below 45 mK is most likely caused by a general thermal decoupling of the detector from the heat bath
bath
Au:Er, 750 ppm
LTD12, Paris
Fluorescence spectrum of 55Mn
Baseline
• 17700 events (50 minutes)
• rate: ~ 15 events/s
• T = 30 mK, IF = 55 mA
Averaged Kα-pulse
IF = 40
mA
T = 39
mK
time
Kα-line
EFWHM=162 eV EFWHM=106 eV
LTD12, Paris
Signal size and Heat capacity
measured signalsize is 30% - 50% smaller than the expected behaviour
measured heat capacity is a factor of 1.3 – 2 larger than the expected behaviour
additional heat capacity and/or loss of phonons
LTD12, Paris
Summary & Outlook
meander: promising geometry
reduced cross talk
reduced magn. Johnson noise
no external field coil needed
better SNR
results: magnetisation of the sputter deposited Au:Er shows bulk properties down to 45
mK
sensor can reliably be microstructured
microstructured detektor shows promising results
future: continue with microstructering ...
arrays + multiplexing
theory
Au:Er, 750 ppm