| 研究課題/領域番号 |
26400340
|
|---|
| 研究機関 | 沖縄科学技術大学院大学 |
|---|
研究代表者 |
コンスタンチノフ デニス 沖縄科学技術大学院大学, Quantum Dynamics Unit, 准教授 (50462685)
|
|---|
| 研究期間 (年度) |
2014-04-01 – 2017-03-31
|
| キーワード | NMR / heterodyne detection |
|---|
| 研究実績の概要 |
The purpose of this research is to investigate the non-linear NMR in antiferromagnetic and weak ferromagnetic materials with strong hyperfine interaction between the electron and nuclear spin systems in order to observe indications of the Bose-Einstein condensation of nuclear spin waves. The later is predicted theoretically to occur at high microwave pumping rate that overcomes dissipation due to spin-lattice relaxation.
In accordance with the proposed plan, we have designed and assembled an NMR spectrometer for CW measurements operating at the frequency of about 600 MHz. Using heterodyne detection scheme, we could measure both absorption and dispersion signals of a non-linear NMR in a MnCO3 weak ferromagnetic sample. This is significantly different from the previously reported experiments on non-linear NMR in MnCO3 samples, where only absorption signal was measured using a homodyne detection scheme with a simple RF detector.
We found that there is a significant contribution to the dispersion signal of NMR, presumably from the electron-spin subsystems This contribution has been not taken into account in the analysis of the previous experiments. Thus we conclude that the interpretation of the previous experiments, where the observation of the Bose-Einstein condensation of nuclear spin waves was clamed, is not correct. In order to separate contribution from the electron-spin subsystems to the non-linear NMR signal, we currently analyze the measured dispersion signals using numerical modeling of the spin dynamics of coupled electron-nuclear spin system.
|
| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
The research progressed rather smoothly during the past fiscal year. It was conducted according to the plan for FY2014 submitted with the proposal. We successfully constructed the heterodyne 600 MHz spectrometer, which enabled us to measure both absorption and dispersion signals of the non-linear NMR simultaneously and separately. The results of NMR measurements in a MnCO3 sample obtained with this spectrometer are very interesting but need further theoretical analysis. In particular, we need to separate contribution to the dispersion signal from the electron subsystem in order to look for evidences of the BEC in nuclear spin waves. This is important because, as we found out from our analysis of the previously reported experimental results, neglecting this contribution results in overestimation of the total signal and incorrect conclusions regarding evidences of BEC in this materials. Help from theoreticians might be necessary, and currently we are contacting some theoreticians to establish collaborative work on this topic.
|
| 今後の研究の推進方策 |
During this fiscal year, we plan to continue working on the analysis of our experimental data obtained during the past fiscal year. Currently, we are working on the modeling of the dynamics of the coupled electron-nuclear spin system by solving numerically the coupled Bloch equations for electron and nuclear magnetization. Depending on the progress and results of our calculations, we might need to carry out more CW non-linear NMR experiments in our MnCO3 sample. In addition, similar measurements in other antiferromagnet samples, such as CsMnF3 or RbMnF3, can be conducted and analyzed using similar methods. The publication reporting results and analysis of our CW measurements will be prepared.
Next, we plan to proceed in accordance with the proposed plan and construct an NMR spectrometer for pulsed measurements. For this purpose, we have already purchased a 100 MHz Radio Processer for RF generation and data acquisition. We will use the same heterodyne scheme employed earlier to up-convert the 100 MHz excitation from the Radio Processor into 600 MHz drive and excite NMR in our MnCO3 sample. The down-converted signal from NMR will be processed by the same Radio Processor, which already contains a high-speed and high-resolution ADC. We aim at observing evidences of BEC of nuclear spin waves by looking for signals with long relaxation time. Pulse echo technique will be also employed using this setup.
|
| 次年度使用額が生じた理由 |
Because we have already had necessary parts to construct the heterodyne spectrometer, we did not use all the fund in FY2014. However, we have used some amount of fund to purchase the Radio Processor which will be used for pulsed NMR experiments in this fiscal year.
|
| 次年度使用額の使用計画 |
In this fiscal year, we plan to spend funds for 1. construction of high-quality factor resonators with tunable frequency. This will require purchase of a piezo-electrical transducer and controller to vary the resonator frequency. 2. a high-power RF amplifier for NMR pulsed measurements. 3. a high-gain, low-noise, possibly cryogenic, pre-amplifier for NMR resonator output signal, 4. various RF components, such as HP/LP and BF filters. 5. Travel expense for collaborator visits.
|
