The development of an FPGA-based NMR spectrometer for condensed matter physics and measurements of the static and dynamic properties of the Haldane chain compound NiI2(3,5 lut)4

Head, Jake (2024). The development of an FPGA-based NMR spectrometer for condensed matter physics and measurements of the static and dynamic properties of the Haldane chain compound NiI2(3,5 lut)4. University of Birmingham. Ph.D.

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Abstract

Nuclear magnetic resonance (NMR) techniques can be used to probe the local magnetic environment of a compound. Over time, advancements in computing have led to the digitisation of NMR spectrometers in order to provide more stable and efficient measurement instruments. This thesis presents a fully digitised NMR spectrometer based on a field programmable gate array (FPGA) for use in condensed matter NMR experiments. The transmitter can generate three, phase-configurable, RF pulses of frequencies up to 800 MHz, whilst the receiver can process signals up to 400 MHz. The full NMR set-up was tested by successfully measuring the spin echo signal from 59Co powder at 213 MHz. Quantum spin models have been a subject of interest in condensed matter physics since their introduction in theearly 20th century. The range of interactions within these models has led to the observation of a wide variety of exotic quantum phenomena. In particular, the Spin-1 chain hosts an exotic gapped state where there is a finite energy gap between the ground and excited states. This thesis presents magnetisation, heat capacity and 13C NMR measurements on the Spin-1 chain sample NiI2(3 ,5 lut)4 to characterise the predicted attractive Tomonaga-Luttinger liquid (TLL) state. The magnetisation measurements investigated scaling behaviour around the low-field quantum critical point at the critical field Hc = 4.4 T but demonstrated poor agreement with the theoretical predictions. The heat capacity measurements found no evidence for the existence of the TLL phase down to a temperature of 2 K. The 13C relaxation time constant T1 was found to follow a power law dependence on temperature with an exponent of approximately α = −1.25, outside the range of an attractive TLL.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):