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EPR setup

Two experimental techniques have been largely used in the study of the magnetic properties of SMMs in their solid state form: Magnetometry and EPR spectroscopy. Particularly, homemade micro-Hall effect, micro-SQUID magnetometers, and resonant cavity EPR spectrometers have lead to spectacular advances in the understanding of QTM in SMMs. EPR spectroscopy allows for probing of the energy landscape related to the interaction between the spin of the molecules and an externally applied magnetic field. The frequencies generally employed in EPR spectrometers range from tens up to hundreds of gigahertzs. Notably for SMMs this energy range coincides with those associated with transitions between the spin levels of the molecule in its ground state. More interestingly, moderately low magnetic fields (<10 Tesla) can be employed to tune any magnetic transition into resonance with the energy of the microwave radiation, thus allowing a complete determination of the parameters of the Hamiltonian describing the anisotropic nature of the molecular spin.

Below we show the experimental setup that allows us to carry EPR spectroscopy measurements in a broad range of experimental conditions, such as frequency (10-110 GHz), temperature (15 mK - RT), magnetic fields (8 T), pulses (>1ns)
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FIGURE: Scheme of pulse EPR experimental configurations for frequency ranges 1-50 GHz (A) and 50-110GHz (B). List of components shown: 1) Dewar housing He4, He3 and He3/He4-dilution cryostats (15mK-300K) and a superconducting vector magnet (0-8T); 2) Microstrip resonator housing box; 3) Superconducting magnet capable of applying a vector field at arbitrary directions; 4) Semi-rigid 0.086” coaxial lines (SS and Cu) wiring the cryostats; 5) >0.3ns pulse pattern generator; 6) Agilent vector network analyzer (0-50GHz); 7) High frequency microwave pulse generation circuit (dc-40GHz). Includes ultra-fast-response microwave switch (>2ns pulse width), 3 high-frequency amplifiers (20dBm output power below 40GHz, 30dBm output power below 25GHz), directional coupler and video filter; 8) Frequency extension modules (up to 110GHz); 9) V-band waveguides on the He4 probe (>30GHz); 10) High-Q resonant cavity.
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