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Probing GHz Spin Dynamics Across Magnetic Phase Transitions in CrCl3 Nanoflakes Using Nitrogen-Vacancy Microscopy
Authors:
Benjamin Hammons,
Jitender Kumar,
Sehrish Iqbal,
Prem Bahadur Karki,
Karishma Prasad,
Tianlin Li,
Aram Pirali,
Ayodimeji E. Aregbesola,
Rupak Timalsina,
Xia Hong,
Jian Wang,
Kapildeb Ambal,
Ilja Fescenko,
Abdelghani Laraoui
Abstract:
CrCl3, a layered van der Waals (vdW) magnet, exhibits in-plane magnetic anisotropy and enhanced interlayer coupling upon stacking, making it an ideal platform to host exotic nanoscale magnetic phenomena such as magnon hydrodynamics and meron-like topological spin defects. When interfaced with other vdW materials, its antiferromagnetic-to-ferromagnetic and ferromagnetic-to-paramagnetic phase transi…
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CrCl3, a layered van der Waals (vdW) magnet, exhibits in-plane magnetic anisotropy and enhanced interlayer coupling upon stacking, making it an ideal platform to host exotic nanoscale magnetic phenomena such as magnon hydrodynamics and meron-like topological spin defects. When interfaced with other vdW materials, its antiferromagnetic-to-ferromagnetic and ferromagnetic-to-paramagnetic phase transitions and magnetic anisotropy can be tuned by voltage, strain, and layer stacking. Understanding the spin dynamics of CrCl3 at its magnetic phase transitions is crucial to its applications in magnonics. Here, we investigate the spin dynamics of CrCl3 nanoflakes using cryogenic diamond quantum sensing microscopy, based on measuring optically detected magnetic resonance, Rabi oscillations, and spin-lattice relaxation time (T1) of shallow nitrogen vacancy (NV) centers in diamond. In the ferromagnetic regime, we observe a pronounced reduction in the NV spin resonance contrast, a collapse of the Rabi oscillations, and a strong enhancement by two orders of magnitude of the relaxation rate G1 = 1/T1. These observations indicate intensified spin fluctuations in the gigahertz range. Broadband ferromagnetic resonance spectroscopy on CrCl3 crystals reveals resonance frequencies in the 4-15 GHz range together with a linewidth of ~24 mT, further supporting the NV measurements. A phenomenological model of magnetic-noise-induced NV relaxation reproduces the temperature dependence of G1 by combining antiferromagnetic, ferromagnetic, and paramagnetic fluctuation channels, indicating that magnetic noise is strongest in the ferromagnetic regime and evolves markedly across the phase transition. These results are crucial for using CrCl3 in 2D magnonics and hybrid quantum-magnon systems.
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Submitted 20 July, 2026; v1 submitted 27 April, 2026;
originally announced April 2026.
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Spin Dynamics in the van der Waals Ferromagnet CrTe2 Engineered by Niobium Doping
Authors:
Dhan Raj Lawati,
Prem Bahadur Karki,
Jitender Kumar,
Karishma Prasad,
Mohamed A. Elekhtiar,
Kai Huang,
Bibek Tiwari,
Suvechhya Lamichhane,
Rupak Timalsina,
Zane Hubble,
Ayodimeji E. Aregbesola,
John Watt,
Sy-Hwang Liou,
Evgeny Y. Tsymbal,
Jian Wang,
Kapildeb Ambal,
Abdelghani Laraoui
Abstract:
Understanding and controlling spin dynamics in two-dimensional (2D) van der Waals (vdW) ferromagnets is essential for their application in magnonics and hybrid quantum platforms. Here, we investigate the spin dynamics of the vdW ferromagnet 1T-CrTe_{2} and demonstrate their systematic tunability via niobium (Nb) substitution in Cr_{1-x}Nb_{x}Te_{2}(x=0-0.2). Ferromagnetic resonance (FMR) spectrosc…
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Understanding and controlling spin dynamics in two-dimensional (2D) van der Waals (vdW) ferromagnets is essential for their application in magnonics and hybrid quantum platforms. Here, we investigate the spin dynamics of the vdW ferromagnet 1T-CrTe_{2} and demonstrate their systematic tunability via niobium (Nb) substitution in Cr_{1-x}Nb_{x}Te_{2}(x=0-0.2). Ferromagnetic resonance (FMR) spectroscopy reveals that Nb doping enables wide-band tuning of the resonance frequency from 40 GHz down to the few-GHz regime, accompanied by a moderate increase in the Gilbert damping constant from ~0.066 to ~0.14, while preserving robust room-temperature ferromagnetism. Complementary magnetometry shows a concurrent reduction of the Curie temperature and saturation magnetization with increasing Nb content. Density functional theory calculations attribute the observed spin-dynamic trends to Nb-induced modifications of magnetic anisotropy and magnetic exchange interactions. Furthermore, CrTe_{2} flakes (~80 nm thick) exhibit lower resonance frequencies and damping than bulk crystals, consistent with thickness, surface/interface, and shape-dependent magnetic anisotropy. These results establish Nb-doped CrTe_{2} as a tunable vdW ferromagnet with controllable spin dynamics, extending its functionality from spintronics to broadband magnonics and quantum magnonics.
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Submitted 4 May, 2026; v1 submitted 26 December, 2025;
originally announced December 2025.
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An efficient and low-cost method to create high-density nitrogen-vacancy centers in CVD diamond for sensing applications
Authors:
Prem Bahadur Karki,
Rupak Timalsina,
Mohammadjavad Dowran,
Ayodimeji E. Aregbesola,
Abdelghani Laraoui,
Kapildeb Ambal
Abstract:
The negatively charged Nitrogen-Vacancy (NV-) center in diamond is one of the most versatile and robust quantum sensors suitable for quantum technologies, including magnetic field and temperature sensors. For precision sensing applications, densely packed NV- centers within a small volume are preferable due to benefiting from 1/N^1/2 sensitivity enhancement (N is the number of sensing NV centers)…
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The negatively charged Nitrogen-Vacancy (NV-) center in diamond is one of the most versatile and robust quantum sensors suitable for quantum technologies, including magnetic field and temperature sensors. For precision sensing applications, densely packed NV- centers within a small volume are preferable due to benefiting from 1/N^1/2 sensitivity enhancement (N is the number of sensing NV centers) and efficient excitation of NV centers. However, methods for quickly and efficiently forming high concentrations of NV- centers are in development stage. We report an efficient, low-cost method for creating high-density NV- centers production from a relatively low nitrogen concentration based on high-energy photons from Ar+ plasma. This study was done on type-IIa, single crystal, CVD-grown diamond substrates with an as-grown nitrogen concentration of 1 ppm. We estimate an NV- density of ~ 0.57 ppm (57%) distributed homogeneously over 200 um deep from the diamond surface facing the plasma source based on optically detected magnetic resonance and fluorescence confocal microscopy measurements. The created NV-s have a spin-lattice relaxation time (T1) of 5 ms and a spin-spin coherence time (T2) of 4 us. We measure a DC magnetic field sensitivity of ~ 104 nT Hz^-1/2, an AC magnetic field sensitivity of ~ 0.12 pT Hz^-1/2, and demonstrate real-time magnetic field sensing at a rate over 10 mT s-1 using an active sample volume of 0.2 um3.
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Submitted 20 January, 2023;
originally announced January 2023.
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Locking and Tracking Magnetic Resonance Spectra of NV- Center for Real-time Magnetometry using a Differential Photon-Rate Meter
Authors:
Kapildeb Ambal,
Robert D. McMichael
Abstract:
We describe a real-time data processing and frequency control method to track peaks in optically detected magnetic resonance of nitrogen-vacancy centers in diamond. This procedure allows us to measure magnetic field continuously with sensitivity ~6 uT/Hz^{1/2} and to track resonances at sweep rates exceeding 110 uT/s. We use a custom-built differential photon rate meter and active feedback control…
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We describe a real-time data processing and frequency control method to track peaks in optically detected magnetic resonance of nitrogen-vacancy centers in diamond. This procedure allows us to measure magnetic field continuously with sensitivity ~6 uT/Hz^{1/2} and to track resonances at sweep rates exceeding 110 uT/s. We use a custom-built differential photon rate meter and active feedback control to "lock" the microwave excitation frequency of the magnetic resonance. Our scheme covers a broad magnetic field range, limited by the frequency range of the microwave generator. This measurement procedure automates the processing of voltage pulse outputs from the photon counters, and it provides sensitivity comparable to traditional photon counting methods
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Submitted 16 August, 2018;
originally announced August 2018.
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Separating hyperfine from spin-orbit interactions in organic semiconductors by multi-octave magnetic resonance using coplanar waveguide microresonators
Authors:
Gajadhar Joshi,
Richards Miller,
Lillie Ogden,
Marzieh Kavand,
Shirin Jamali,
Kapildeb Ambal,
Suresh Venkatesh,
David Schurig,
Hans Malissa,
John M. Lupton,
Christoph Boehme
Abstract:
Separating the influence of hyperfine from spin-orbit interactions in spin-dependent carrier recombination and dissociation processes necessitates magnetic resonance spectroscopy over a wide range of frequencies. We have designed compact and versatile coplanar waveguide resonators for continuous-wave electrically detected magnetic resonance, and tested these on organic light-emitting diodes. By ex…
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Separating the influence of hyperfine from spin-orbit interactions in spin-dependent carrier recombination and dissociation processes necessitates magnetic resonance spectroscopy over a wide range of frequencies. We have designed compact and versatile coplanar waveguide resonators for continuous-wave electrically detected magnetic resonance, and tested these on organic light-emitting diodes. By exploiting both the fundamental and higher-harmonic modes of the resonators we cover almost five octaves in resonance frequency within a single setup. The measurements with a common pi-conjugated polymer as the active material reveal small but non-negligible effects of spin-orbit interactions, which give rise to a broadening of the magnetic resonance spectrum with increasing frequency.
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Submitted 11 March, 2016;
originally announced March 2016.
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An atomic resolution, single-spin magnetic resonance detection concept based on tunneling force microscopy
Authors:
A. Payne,
K. Ambal,
C. Boehme,
C. C. Williams
Abstract:
A comprehensive study of a force detected single-spin magnetic resonance measurement concept with atomic spatial resolution is presented. The method is based upon electrostatic force detection of spin-selection rule controlled single-electron tunneling between two electrically isolated paramagnetic states. Single spin magnetic resonance detection is possible by measuring the force detected tunneli…
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A comprehensive study of a force detected single-spin magnetic resonance measurement concept with atomic spatial resolution is presented. The method is based upon electrostatic force detection of spin-selection rule controlled single-electron tunneling between two electrically isolated paramagnetic states. Single spin magnetic resonance detection is possible by measuring the force detected tunneling charge noise on and off spin resonance. Simulation results of this charge noise, based upon physical models of the tunneling and spin physics, are directly compared to measured AFM system noise. The results show that the approach could provide single spin measurement of electrically isolated qubit states with atomic spatial resolution at room temperature.
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Submitted 30 January, 2015;
originally announced February 2015.
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Synthesis of thin silicon dioxide layers with high E' center densities and investigation of the E' center spin relaxation dynamics for single spin readout applications
Authors:
K. Ambal,
A. Payne,
D. P. Waters,
C. C. Williams,
C. Boehme
Abstract:
Methods for the creation of thin amorphous silicon dioxide (aSiO2) layers on crystalline silicon substrates with very high densities of silicon dangling bonds (so called E' centers) have been explored and volume densities of [E']> 5x10^18 cm-3 throughout a 60nm thick film have been demonstrated by exposure of a thermal oxide layer to a low pressure Argon radio frequency plasma. While the generated…
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Methods for the creation of thin amorphous silicon dioxide (aSiO2) layers on crystalline silicon substrates with very high densities of silicon dangling bonds (so called E' centers) have been explored and volume densities of [E']> 5x10^18 cm-3 throughout a 60nm thick film have been demonstrated by exposure of a thermal oxide layer to a low pressure Argon radio frequency plasma. While the generated high E' center densities can be annealed completely at 300C, they are comparatively stable at room temperature with a half life of about one month. Spin relaxation time measurements of these states between T = 5K and T = 70K show that the phase relaxation time T2 does not strongly depend on temperature and compared to SiO2 films of lower E' density, is significantly shortened. The longitudinal relaxation time T1 ~195(5)us at room temperature is in agreement with low-density SiO2. In contrast, T1 ~625(51)us at T = 5K is much shorter than in films of lower E' density. These results are discussed in the context of E' centers being used as probe spins for spin-selection rules based single spin-readout.
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Submitted 30 September, 2013;
originally announced October 2013.