Analytical Instrument Documents

rss

JEOL Resources

Documentation in support of your JEOL product.

Strong interaction between light and electrons (4) "Transmission ESR/FMR measurement method"

Interaction between microwave photon and spins means in other words, interaction between resonating photon in a closing space and spins. Thus, measuring spectra using a non-resonant device can prevent the Purcell effect or strong coupling from distortion of intrinsic spectra. Figure 1(a) is a drawing expressing a typical spectroscopy. A light source irradiates light to a sample, and transmitted light is detected. A simple and non-resonant wave guide, as shown in Fig.1(b), can provide absorption spectra of para- and ferromagnetic samples which have a high spin density.

Strong interaction between light and electrons (2) "Four states of interaction between photon and spins"

A conventional ESR spectrometer uses a cavity for microwave irradiation and detection of ESR absorption. On the resonance state, it can be considered as a model that spins absorb energy of ℎ𝜈=𝑔𝜇𝐵𝐵 and then release it to the lattice system one way, where h: Planck constant, ν: frequency, g: g-value, μB: Bohr magneton, and B: magnetic flux density. However, the interaction between photon of microwave and spins of electrons is a little more complex in fact. Figure 1 is a modelized drawing that expresses energy flow of microwave photon and spins. The cavity resonates with angular frequency 𝜔c, relaxes with velocity of 𝜅𝑐=𝜔𝑐 / 𝑄𝑢 , which is inversely proportional to unloaded Q value of the cavity. On the other hand, spins do precess with an angular frequency of 𝜔𝑚= 𝛾𝑒 𝐵𝑚 under the static magnetic field 𝐵𝑚. When the resonant condition of 𝜔𝑐 = 𝜔𝑚 is satisfied, excited electron spins that absorbed microwave energy relax with the velocity of 𝛾𝑚 (half width: half width at half maximum (HWHM)), which corresponds to spectral line width. At this time, photon and electron spins exchange energy with a coupling constant 𝑔𝑚. The coupling constant 𝑔𝑚 is expressed as[1] 数式 where 𝜂𝑚𝑠𝑞𝑟𝑡 is the square root of the filling factor of the cavity, 𝛾𝑒 is gyromagnetic ratio of the electron, ℏ is reduced Planck constant (h/2π), 𝜇0 is vacuum permeability, 𝑉𝑐 is the volume of the cavity, N is number of magnetic ions, and S is spin quantum number.

Strong interaction between light and electrons (1) "Effect of excessive spins"

Typical electron spin resonance (ESR) spectrometer uses a microwave resonator, which is usually called a cavity, as a sensitive detector. A sample is usually set in the center of the cavity, and energy absorption by ESR phenomena is detected according to the degree of an impedance mismatching of the resonant circuit of the cavity. Absorption intensity in the ESR and FMR (Ferromagnetic Resonance) is proportional to the square root of the irradiated microwave power and the spin amount in the measured sample. Moreover, the spectral line width is proportional to the inverse of the transverse relaxation time of spins. The cavity is a device that stores only the light, of which the frequency is 𝜔𝑐=2𝜋𝑓𝑐, in the limited space. Electron spins lied in a static magnetic field are like spinning tops which are locked to specific Larmor frequency (𝜔𝑟=2𝜋𝑓𝑟). ESR/FMR spectrum is usually measured in the condition of 𝜔𝑐=𝜔𝑟. Recently, many attentions are gathering to the interaction between light (microwave) and spins in the cavity according to the development of quantum optics.

Strong interaction between light and electrons (3) "Strong coupling state of ferromagnetic thin film"

Coupling constant (𝑔𝑚) between microwave photon and electron spins is proportional to the square root of spin numbers as shown in eq.(1) of "Application Note ER200007E ". Therefore, FMR measurements using ferromagnets which include many spins and especially have narrow line widths do not work well, because spins in ferromagnets interact strongly with microwave photon, and achieve to "strong coupling" state larger than the state of "Purcell effect". Figure 1(a) is an example that shows the obtained unexpected spectrum in the strong coupling state. Normal FMR spectrum can be obtained as shown in Fig.1(d), if the filling factor is reduced and the system moves to a "weak coupling" state.

Application for fluorine compounds_NM200004E

The ROYALPROBE™ HFX can simultaneously irradiate 1H, 19F, and 13C (or other X-nuclei) even in a basic console with basic two-channel console, and is a versatile probe that can measure a wide-variety of nuclei at high sensitivity. Here we introduce some useful experiments for fluorine-containing compounds that can be run on conjunction with JNM-ECZ400S equipped with ROYALPROBE™ HFX.

Experimental set-up of high-resolution 1H solid-state NMR by wPMLG_NM200010E

1H, in principle, is very useful nucleus to investigate atomic-resolution structures and dynamics due to its high abundance (>99%) and gyromagnetic ratio (600 MHz at 14.1T). In fact 1H is the first choice of nucleus in solution NMR. On the other hand, 1H NMR of rigid solids is much less common. This is because 1H solid-state NMR gives very broad (~50 kHz) and featureless spectra (Fig 1a) due to strong 1H-1H dipolar coupling, which is dynamically averaged out in solution. Magic angle spinning (MAS) removes the broadening to the first order, but is not enough to achieve high resolution 1H NMR at moderate MAS rate (Fig 1b). Tremendous efforts were made to overcome this issue from the early dates of solid-state NMR towards high-resolution 1H NMR [1]. Most of them combine MAS with sophisticated 1H pulses which is dubbed CRAMPS (combined rotation and multiple pulse spectroscopy). Nowadays very fast MAS > 60 kHz can be used to achieve high-resolution 1H solid-state NMR (Fig 1c) [2]. However, the traditional CRAMPS is still useful as that can be performed with very conventional solid-state NMR equipment, for example 4 mm MAS probe with a 400 MHz spectrometer. Moreover, wPMLG at moderate MAS rate often overwhelms fast MAS in terms of resolution. In this note, we will describe tutorial guidance to optimize experimental parameters for CRAMPS.

Other Resources

The following resources are available for the JEOL Analytical Instruments:

Media

Corona - Glow Discharge (DART Ion Source)

January 28, 2022
2343