Nuclear Magnetic Resonance Frequency Research Articles

Anion and cation dynamics in a carbon-substituted cesium closo-hydroborate CsCB11H12: 1H and 133Cs NMR studies

Cesium monocarba-hydroborate CsCB11H12 belongs to the family of alkali-metal closo- hydroborate salts which are considered as promising solid electrolytes for battery applications. To study the dynamical properties of this compound at the microscopic level, we have measured the 1H and 133Cs nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates over the temperature range of 80–434 K. Our measurements have revealed a coexistence of two types of reorientational jump processes of the complex [CB11H12]− anions. For the faster of these processes characterized by the average activation energy of 310 meV, the anion reorientations are not “frozen” at the NMR frequency scale down to 120 K. The behavior of the 133Cs NMR line width in CsCB11H12 is consistent with the onset of long-range diffusive motion of Cs+ ions at the frequency scale of ∼104 s−1 above 340 K, and the distinct effects of the diffusive Cs+ jumps on both the 1H and 133Cs spin-lattice relaxation rates become observable above 380 K.

Optimized Unilateral Magnetic Resonance Sensor with Constant Gradient and Its Applications in Composite Insulators

In this study, an optimized unilateral magnetic resonance sensor with a three-magnet array is presented for assessing the aging of composite insulators in power grids. The sensor’s optimization involved enhancing the static magnetic field strength and the homogeneity of the RF field while maintaining a constant gradient in the direction of the vertical sensor surface and maximizing homogeneity in the horizontal direction. The center layer of the target area was positioned 4 mm from the coil’s upper surface, resulting in a magnetic field strength of 139.74 mT at the center point of the area, with a gradient of 2.318 T/m and a corresponding hydrogen atomic nuclear magnetic resonance frequency of 5.95 MHz. The magnetic field uniformity over a 10 mm × 10 mm range on the plane was 0.75%. The sensor measured 120 mm × 130.5 mm × 76 mm and weighed 7.5 kg. Employing the optimized sensor, magnetic resonance assessment experiments were conducted on composite insulator samples utilizing the CPMG (Carr–Purcell–Meiboom–Gill) pulse sequence. The T2 distribution provided visualizations of the T2 decay in insulator samples with different degrees of aging.

Dynamical properties of the magnesium borohydride – ethylenediamine compound Mg(en)1.2(BH4)2: A nuclear magnetic resonance study

The magnesium borohydride – ethylenediamine (en) compound Mg(en)1.2(BH4)2 exhibits high Mg-ion conductivity above room temperature. To study the dynamical properties of this compound and its partially deuterium-substituted counterpart, we have measured the 1H, 2D, and 11B nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates over a wide temperature range (6–324 K). Our measurements have revealed a coexistence of four types of BH4 reorientational jump processes with different activation energies. For the fastest of these processes characterized by the activation energy of 47(3) meV, the unusually high reorientational mobility is retained down to low temperatures, so that the corresponding H jump rate is of the order of 108 s−1 near 70 K. The presence of fast reorientational motion of [BH4]− anions in Mg(en)1.2(BH4)2 supports the idea that anion reorientations may facilitate the cation diffusion. In the studied temperature range, we have not found any distinct signs of localized motion of the ethylenediamine molecules or their fragments at the NMR frequency scale.

LONGITUDINAL RELAXATION OF NUCLEAR MAGNETIZATION IN RUBBER SOLUTIONS: POLYISOPRENE PROTONS

The longitudinal (spin-lattice) relaxation times of Т1 of protons are measured selectively (for various structural groups) at a nuclear magnetic resonance frequency of 700 MHz in a solution of an industrial sample of Cariflex-IR0307 isoprene rubber in deuterated benzene. It is shown that the value of T1 significantly
 depends on the structural position in the polyisoprene chain. The highest values of T1 are obtained at double bonds of monomer units in the cis-configuration and the methyl group of the trans-unit, the smallest values were obtained for the methine and methylene protons of the 3,4-unit, with a difference of two to three times. The questions of measurement accuracy are considered. Practical recommendations are formulated for the conditions of recording high-resolution NMR1H spectra at quantitative analysis of the structure of isoprene rubbers.

The Rb-Xe coupling effect in optically pumped NMR gyroscopes

Optically pumped nuclear magnetic resonance (NMR) gyroscope has been widely concerned as a future gyroscope with great development potential. In this study, the Rb-Xe coupling effect in this gyroscope between the alkali metal magnetometer and the noble gas NMR is investigated. The theoretical formulae about this effect are obtained based on Bloch equation and demonstrated by experiments. In order to see the influence of this effect on the gyro signal, the Xe NMR frequency changes with the carrier frequency and demodulation phase of the Rb magnetometer are studied with the deduced formulae. More importantly, theoretical analysis shows that this coupling effect can also significantly reduce the efficiency of the dual species scheme, which is used to suppress the influence of magnetic fluctuation. Therefore, to remove the Rb-Xe coupling effect, a simple and preliminary decoupling scheme operated by locking the phase difference to zero is proposed and demonstrated. All this work is of great significance to the improvement of the NMR gyro performance and future applications.

Ammonia: The molecule for establishing 14N and 15N absolute shielding scales and a source of information on nuclear magnetic moments.

Multinuclear Nuclear Magnetic Resonance (NMR) studies of the gaseous mixtures 3He/14NH3 and 3He/15NH3 are reported. Precise analysis of the 3He, 14N, 15N, and 1H resonance frequencies show a linear dependence on the gas density. Extrapolation of these results to the zero-pressure limit gives ν0(1H), ν0(14N), and ν0(15N) resonance frequencies of the isolated ammonia molecule at 300K. The analogous value for 3He atoms in gaseous mixtures ν0(3He) was measured as well. The application of a new scheme to introduce the most important electronic effects on NMR shieldings, together with highly accurate quantum chemical shielding calculations, allows the 14/15N and 1H shielding of the isolated ammonia molecule to be obtained with the greatest accuracy and precision. For the first time, these studies were carried out on ammonia within the so-called four-component relativistic framework. The NMR frequency comparison method provides an approach for determining the 14N and 15N nuclear magnetic moments. The new shielding parameters in ammonia were used for re-evaluation of the entire nitrogen absolute shielding scale. Additionally, the absolute shielding values of several gaseous compounds and secondary reference substances in liquids were presented. It was established that 14N and 15N absolute shielding constants in 14NH3 and 15NH3 are very similar and only differ by less than 0.01 ppm, which is not usually measurable in NMR experiments. Precise calculations of 14N and 15N dipole moments were also made from these accurate shielding values.

Diffuse reflectance spectroscopy characterises the functional chemistry of soil organic carbon in agricultural soils

AbstractSoil organic carbon (SOC) originates from a complex mixture of organic materials, and to better understand its role in soil functions, one must characterise its chemical composition. However, current methods, such as solid‐state 13C nuclear magnetic resonance (NMR) spectroscopy, are time‐consuming and expensive. Diffuse reflectance spectroscopy in the visible, near infrared and mid‐infrared regions (vis–NIR: 350–2500 nm; mid‐IR: 4000–400 cm−1) can also be used to characterise SOC chemistry; however, it is difficult to know the frequencies where the information occurs. Thus, we correlated the C functional groups from the 13C NMR to the frequencies in the vis–NIR and mid‐IR spectra using two methods: (1) 2‐dimensional correlations of 13C NMR spectra and the diffuse reflectance spectra, and (2) modelling the NMR functional C groups with the reflectance spectra using support vector machines (SVM) (validated using 5 times repeated 10‐fold cross‐validation). For the study, we used 99 mineral soils from the agricultural regions of Sweden. The results show clear correlations between organic functional C groups measured with NMR and specific frequencies in the vis–NIR and mid‐IR spectra. While the 2D correlations showed general relationships (mainly related to the total SOC content), analysing the importance of the wavelengths in the SVM models revealed more detail. Generally, models using mid‐IR spectra produced slightly better estimates than the vis–NIR. The best estimates were for the alkyl C group (R2 = 0.83 and 0.85, vis–NIR and mid‐IR, respectively), and the O/N‐alkyl C group was the most difficult to estimate (R2 = 0.34 and 0.38, vis–NIR and mid‐IR, respectively). Combining 13C NMR with the cost‐effective diffuse reflectance methods could potentially increase the number of measured samples and improve the spatial and temporal characterisation of SOC. However, more studies with a wider range of soil types and land management systems are needed to further evaluate the conditions under which these methods could be used.Highlights Diffuse reflectance spectroscopy was used to characterise and model SOC functional chemistry. NMR derived C functional groups could be modelled with vis‐NIR and mid‐IR diffuse reflectance spectra. The methods allow for characterisation of SOC chemical composition on whole mineral soil samples. The approach can improve the spatial and temporal characterisation of SOC composition.

NMR Spectroscopy for Proof-of-Concept Experimentation on a Polarized Laser Fusion Process

A test experiment to polarize tritium nuclei to develop a polarized deuterium-tritium (D-T) laser fusion concept is proposed in which a ferromagnetic complex with a high internal magnetic field is used to polarize tritium nuclei on physisorbed D-T molecules with an internal β-decay heat load in a D-T target. Heteronuclear hydrogen deuteride (HD) is used to conduct the measurements herein instead of as in typical D-T–based experiments. As proof-of-concept experimentation, the adsorption and desorption characteristics of HD are examined on Prussian blue ferromagnetic analogue Ni3[Fe(CN)6]2 at temperatures of 77 K and around 23 K. Nuclear magnetic resonance (NMR) analysis of the ferromagnetic complex-mediated adsorption of HD onto activated carbon pellets at 10 K is conducted step by step using a multilocular probe cell that had been simplified to give a single-tube probe cell. The resulting 1H NMR spectra are compared with 19F NMR spectra obtained for reference on a Kel-F probe cell wall. Slight differences between the calculated NMR frequency from the gyromagnetic ratio and the actually observed NMR frequency are also discussed.

Accurate Rock Mineral Characterization With Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) logging is a powerful formation evaluation technology that provides mineralogy-independent porosity and helps distinguish clay-bound water, capillary-bound water, and free fluids. NMR logging tool generally operates at 1H NMR frequency of 2 MHz (magnetic field, B0 ~ 470 Gauss) or lower. At this magnetic field, it is only feasible to detect 1H signal from fluids in pores and rely on the relaxation time variation to characterize fluid and pore types. As magnetic field strength increases, NMR sensitivity increases very dramatically, and NMR signals from solid matrix become easier to be detected in high field. For example, NMR at 600 MHz is about 5,000 times more sensitive than the NMR at 2 MHz. Meanwhile, the spectral resolution of high-field NMR is also greatly increased, and high-field NMR spectrum can resolve the detailed differences between molecule types. Therefore, the high sensitivity and spectral resolution of high-field NMR open a totally new horizon for the characterization of geological samples, especially in organic shale reservoirs, in which organic matter and complex mineralogy remain challenging to be accurately characterized. In this work, we report high-field NMR applications for mineral characterization using a 600-MHz NMR spectrometer equipped with a multichannel and Magic-Angle Spinning (MAS) probe. Compared to X-ray diffraction (XRD), which is the primary tool for identifying and quantifying the mineralogy of crystalline compounds in geological samples based on Bragg’s diffraction, NMR can provide more compositional and structural information for noncrystalline compounds due to its sensitivity to local electronic binding structures. Here we demonstrate such an application of high-resolution 27Al NMR to determine the composition and bonding chemistry of 27Al as a fingerprint for a wide range of minerals. The ratio of 27Al at tetrahedral and octahedral binding sites is quantitative and essential to differentiate the dioctahedral and trioctahedral phases. 27Al NMR can also distinguish plagioclase series members ranging from albite to anorthite end members, where Na and Ca atoms can substitute for each other. 27Al NMR can be further combined with 1H, 13C, 29Si, 25Mg, 23Na, and 31P for more detailed mineral determination and clay typing. Our results show that, combined with XRD, this group of high-field NMR spectroscopic methods can greatly improve the accuracy of rock mineral and formation clay characterization in tight-rock and unconventional reservoirs.

Slow spin dynamics in the hyperhoneycomb lattice [(C2H5)3NH]2Cu2(C2O4)3 revealed by H1 NMR studies

We report the results of magnetic susceptibility $\chi$ and $^1$H nuclear magnetic resonance (NMR) measurements on a three-dimensional hyper-honeycomb lattice compound [(C$_2$H$_5$)$_3$NH]$_2$Cu$_2$(C$_2$O$_4$)$_3$ (CCCO). The average value of the antiferromagnetic (AFM) exchange coupling between the Cu$^{2+}$ ($S$ = 1/2) spins was determined to be $J$~$\sim$~50 K from the $\chi$ measurements. No long-range magnetic ordering has been observed down to $T$ = 50 mK, although NMR lines become slightly broader at low temperatures below 1 K. The broadening of the NMR spectrum observed below 1 K reveals that the Cu spin moments remain at this temperature, suggesting a non-spin-singlet ground state. The temperature and magnetic field dependence of 1/$T_1$ at temperatures above 20 K is well explained by paramagnetic thermal spin fluctuations where the fluctuation frequency of Cu$^{2+}$ spins is higher than the NMR frequency of the order of MHz. However, a clear signature of the slowing down of the Cu$^{2+}$ spin fluctuations was observed at low temperatures where 1/$T_1$ shows a thermally-activated behavior. The magnetic field dependence of the magnitude of the spin excitation gap suggests that the magnetic behaviors of CCCO are characterized as an AFM chain at low temperatures.

Review of recent developments in ultra-high field (UHF) NMR magnets in the Asia region

This paper reviews recent developments in ultra-high field (UHF) superconducting magnets for nuclear magnetic resonance (NMR) in the Asia regionin particular, those for high-resolution NMR magnets using high-temperature superconductor (HTS) coils. In Japan, a power supply driven-mode 1.02 GHz (24.0 T) NMR magnet using a Bi2Sr2Ca2Cu3O10-δ (Bi-2223) inner coil was developed in 2015, providing the first high-resolution NMR at a 1H NMR frequency of >1 GHz (23.5 T). In late 2017, a new project was started to develop a persistent-mode 1.3 GHz (30.5 T) NMR magnet comprising a RE(rare earth)Ba2Cu3O7-δ (REBCO) inner coil, a Bi-2223 middle coil, and a low-temperature superconductor (LTS) outer coil. The magnet employs the newly developed state-of-the-art superconducting joints between HTSs necessary for the persistent-mode operation, as well as magnet technologies providing an ultra-high magnetic field of >30.5 T with high temporal stability and spatiality homogeneity for high-resolution NMR measurement. In China, a ∼20 mm cold bored magnet comprising an LTS outer coil and no-insulation (NI) REBCO inner coils was developed and recorded a field of 32.35 T, the highest magnetic field ever achieved with an all-superconducting magnet, which can be used as a small cold-bored NMR. In Korea, a liquid helium-free 400 MHz (9.39 T) all REBCO NMR magnets using NI winding was developed, which is operational. These technologies provide future perspectives for a UHF NMR magnet with key features of persistent-mode operation, an operating field of 1.4 GHz using (32.9 T)-class magnets, and the liquid helium-free operation.

CeNTREX: a new search for time-reversal symmetry violation in the 205Tl nucleus

The Cold molecule Nuclear Time-Reversal EXperiment (CeNTREX) is a new effort aiming for a significant increase in sensitivity over the best present upper bounds on the strength of hadronic time reversal (T) violating fundamental interactions. The experimental signature will be shifts in nuclear magnetic resonance frequencies of 205Tl in electrically-polarized thallium fluoride (TlF) molecules. Here we describe the motivation for studying these T-violating interactions and for using TlF to do so. To achieve higher sensitivity than earlier searches for T-violation in TlF, CeNTREX uses a cryogenic molecular beam source, optical state preparation and detection, and modern methods of coherent quantum state manipulation. Details of the measurement scheme and the current state of the apparatus are presented, with quantitative measurements of the TlF beam. Finally, the estimated sensitivity and methods to control systematic errors are discussed.

Zero-field 29Si nuclear magnetic resonance signature of helimagnons in MnSi

The low temperature dependence of the nuclear magnetic resonance frequency and spin–lattice relaxation rate measured in the chiral magnet MnSi by Yasuoka and coworkers [J.Phys.Soc.Jpn.85, 073701 (2016)] is interpreted in terms of helimagnon excitations. The theoretically predicted gapless and anisotropic dispersion relation which is probed at extremely small energy is experimentally confirmed. Whenever comparison is possible, the results are found quantitatively consistent with those of the inelastic neutron scattering and muon spin rotation and relaxation techniques. Further studies are suggested.

Design and performance of an in-vacuum, magnetic field mapping system for the Muon g-2 experiment

The Muon g−2 experiment at Fermilab (E989) aims to measure the anomalous magnetic moment, aμ, of the muon with a precision of 140 parts-per-billion. This requires a precise measurement of both the anomalous spin precession frequency, ωa, of muons stored in a magnetic field of 1.45 T, and a precise measurement of that magnetic field in terms of the shielded proton Larmor frequency, ω′p. The measurement of ω′p with a total systematic uncertainty of 70 parts-per-billion involves a combination of various nuclear magnetic resonance (NMR) probes. There are 378 probes mounted in fixed locations that constantly monitor field drifts. A water-based, cylindrical calibration probe provides the calibration in terms of the shielded proton Larmor frequency. A crucial element for the multi-step measurement of ω′p is the regular mapping of the magnetic field over the muon storage region. The former experiment at Brookhaven National Laboratory (BNL) employed an in-vacuum field mapping system equipped with 17 NMR probes, which was developed by the University of Heidelberg. We have refurbished and upgraded this system with new probes and electronics. The upgrades include the addition of 16-bit, 1 MSPS digitization of the NMR signals, which replaced the hardware-implemented zero-crossing counting of the system at Brookhaven. The digitized signals offer new capabilities in the NMR frequency analysis and its related systematic uncertainties. To sustain the higher data rates, a new communication scheme with time-division multiplexing was implemented to separate the important NMR reference clock from the data communication in order to reach the specifications for the accuracy and stability of the reference clock. A new barcode reader provides more precise azimuthal position determination during the measurement and calibration. While the mechanical systems that move the field mapper inside the storage ring have been mostly refurbished from BNL, the motion control system was completely replaced with a custom-built electronics centered around a commercial Galil motion controller. Both the field mapping NMR system and its motion control were successfully commissioned at Fermilab and have been in reliable operation during the first three data taking periods of the experiment at Fermilab. This article will provide the details of the upgrades of the field mapper and its performance.

Qualitative and Quantitative Analysis of Heavy Crude Oil Samples and Their SARA Fractions with 13C Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) approaches have unique advantages in the analysis of crude oil because they are non-destructive and provide information on chemical functional groups. Nevertheless, the correctness and effectiveness of NMR techniques for determining saturates, aromatics, resins, and asphaltenes (SARA analysis) without oil fractioning are still not clear. In this work we compared the measurements and analysis of high-resolution 13C NMR spectra in B0 ≈ 16.5 T (NMR frequency of 175 MHz) with the results of SARA fractioning for four various heavy oil samples with viscosities ranging from 100 to 50,000 mPa·s. The presence of all major hydrocarbon components both in crude oil and in each of its fractions was established quantitatively using NMR spectroscopy. Contribution of SARA fractions in the aliphatic (10–60 ppm) and aromatic (110–160 ppm) areas of the 13C NMR spectra were identified. Quantitative fractions of aromatic molecules and oil functional groups were determined. Aromaticity factor and the mean length of the hydrocarbon chain were estimated. The obtained results show the feasibility of 13C NMR spectroscopy for the express analysis of oil from physical properties to the composition of functional groups to follow oil treatment processes.

Thermal effects versus spin nematicity in a frustrated spin- 12 chain

The spin-nematic phase is an intriguing state of matter that lacks usual long-range dipolar order, yet it exhibits higher multipolar order. This makes its detection extremely difficult and controversial. Recently, nuclear magnetic resonance (NMR) has been proposed as one of the most suitable techniques to confirm its existence. We report a $^{17}$O NMR observation of the reduction of the local magnetization in the polarized state of the frustrated spin-1/2 chain $\beta$-TeVO$_4$, which was previously proposed to be a fingerprint of the spin-nematic behavior. However, our detailed study shows that the detected missing fraction of the magnetization, probed by NMR frequency shift, is thermally activated, thus undermining the presence of the spin-nematic phase in the investigated compound. This highlights the importance of careful considerations of temperature-dependent NMR shift that has been overlooked in previous studies of spin nematicity.

A non-interference method for measurement of transverse relaxation time of the alkali metal magnetometer in nuclear magnetic resonance oscillator

The transverse relaxation time τ2 of the built-in alkali metal magnetometer is an important parameter to characterize its performance and the working state of the nuclear magnetic resonance (NMR) oscillator system. The method we propose to measure τ2 is to apply the frequency-scanning magnetic fields along the x-axis and obtain τ2 from the 3 dB bandwidth of the measured x-axis amplitude–frequency response curve of the magnetometer. We give a detailed and rigorous theoretical derivation by using the perturbation-iteration method to demonstrate the rationality of this measuring method. Then, both the actual experiment and the simulation experiment results are presented to verify the validity and good accuracy of the method. All the sampled frequencies in the scanning range should be far away from both the 129Xe and 131Xe NMR frequencies, to avoid introducing any influence on the nuclear spins; therefore, this method can provide a non-interference way for measurement of τ2, helping us monitor the NMR oscillator system’s state under normal operating conditions.

Elucidating the 1H NMR Relaxation Mechanism in Polydisperse Polymers and Bitumen Using Measurements, MD Simulations, and Models.

The mechanism behind the 1H nuclear magnetic resonance (NMR) frequency dependence of T1 and the viscosity dependence of T2 for polydisperse polymers and bitumen remains elusive. We elucidate the matter through NMR relaxation measurements of polydisperse polymers over an extended range of frequencies (f0 = 0.01-400 MHz) and viscosities (η = 385-102 000 cP) using T1 and T2 in static fields, T1 field-cycling relaxometry, and T1ρ in the rotating frame. We account for the anomalous behavior of the log-mean relaxation times T1LM ∝ f0 and T2LM ∝ (η/T)-1/2 with a phenomenological model of 1H-1H dipole-dipole relaxation, which includes a distribution in molecular correlation times and internal motions of the nonrigid polymer branches. We show that the model also accounts for the anomalous T1LM and T2LM in previously reported bitumen measurements. We find that molecular dynamics (MD) simulations of the T1 ∝ f0 dispersion and T2 of similar polymers simulated over a range of viscosities (η = 1-1000 cP) are in good agreement with measurements and the model. The T1 ∝ f0 dispersion at high viscosities agrees with previously reported MD simulations of heptane confined in a polymer matrix, which suggests a common NMR relaxation mechanism between viscous polydisperse fluids and fluids under nanoconfinement, without the need to invoke paramagnetism.

High-resolution Overhauser dynamic nuclear polarization enhanced proton NMR spectroscopy at low magnetic fields

Dynamic nuclear polarization (DNP) has gained large interest due to its ability to increase signal intensities in nuclear magnetic resonance (NMR) experiments by several orders of magnitude. Currently, DNP is typically used to enhance high-field, solid-state NMR experiments. However, the method is also capable of dramatically increasing the observed signal intensities in solution-state NMR spectroscopy. In this work, we demonstrate the application of Overhauser dynamic nuclear polarization (ODNP) spectroscopy at an NMR frequency of 14.5 MHz (0.35 T) to observe DNP-enhanced high-resolution NMR spectra of small molecules in solutions. Using a compact hybrid magnet with integrated shim coils to improve the magnetic field homogeneity we are able to routinely obtain proton linewidths of less than 4 Hz and enhancement factors >30. The excellent field resolution allows us to perform chemical-shift resolved ODNP experiments on ethyl crotonate to observe proton J-coupling. Furthermore, recording high-resolution ODNP-enhanced NMR spectra of ethylene glycol allows us to characterize the microwave induced sample heating in-situ, by measuring the separation of the OH and CH2 proton peaks.

Effect of aluminium substitution in magnetically affluent inverse spinel ferrites studied via 57Fe-Internal field NMR

Ferro/ferrimagnetic materials are of fundamental interest due to their variety of applications. The structural and magnetic properties change significantly with different synthesis procedures. Here, we report the synthesis, X-Ray Diffraction (XRD), Vibrating Sample Magnetometry (VSM), and Nuclear Magnetic Resonance (NMR) studies of spinel nickel ferrites doped with non-magnetic cations like cadmium and aluminium. The spinel ferrites like Ni0.7Cd0.3Fe2-xAlxO4 (x = 0, 0.1, 0.2) are synthesized using one step auto combustion technique. The X-ray diffraction measurements confirm the formation of these systems in pure phase. In the present study we have used the modified home-built NMR spectrometer to study 57Fe NMR in these ferro magnetic materials. The difference in the Fe3+ bonding at the octahedral (B-site) and the tetrahedral (A-site) sites result in the different hyperfine fields yielding Internal Field (IF) NMR frequencies at two different frequencies. The substitution of the non-magnetic Al3+ results in increasing in the line width of the NMR spectra corresponding to the octahedral site (B-site). Further, the NMR spectra corresponding to A-site decreases (both in terms of line width and area) due to the decrease in the ferrimagnetic contribution at that site. Change in the local environment around Fe3+ ion present at B-site is very well observed using 57Fe NMR technique.