Quantum Sensing of Local Magnetic Phase Transitions and Fluctuations near the Curie Temperature in Tm3Fe5O12 Using NV Centers

At a Glance

Metadata	Details
Publication Date	2025-05-28
Journal	Micromachines
Authors	Yuqing Zhu, Mengyuan Cai, Qian Zhang, Peng Wang, Yuanjie Yang
Institutions	University of Science and Technology of China, Hefei Institutes of Physical Science
Citations	1
Analysis	Full AI Review Included

Executive Summary

This research presents the first quantitative investigation of local dynamic magnetic fluctuations in Thulium Iron Garnet (Tm₃Fe₅O₁₂, TmIG) thin films using Nitrogen-Vacancy (NV) center quantum sensing.

Core Value Proposition: Established a versatile, multimodal framework combining nanoscale NV relaxometry (T₁) with macroscopic techniques (MPMS, Hall effect) to probe local phase transition kinetics in high-temperature magnetic insulators.
Critical Finding: NV T₁ relaxometry revealed a pronounced, quantifiable peak in the net relaxation rate (ΔΓ) near the Curie temperature (T_C ≈ 360 K), providing direct evidence of enhanced critical spin fluctuations at the nanoscale.
Material Quality: High-quality, 20 nm thick TmIG films were fabricated via RF sputtering, exhibiting robust ferromagnetism (H_c = 35 Oe at 300 K) and high crystalline purity (XRD FWHM less than 0.05°).
NV Sensor Performance: The platform achieved submicron lateral spatial resolution (~360 nm) and high dynamic sensitivity (~1.6 µT/sqrt(Hz)), enabling localized measurements inaccessible to conventional volume-averaged methods.
Transport Correlation: Hall measurements corroborated the magnetic findings, showing a prominent resistivity upturn near T_C, attributed to increased spin-disorder scattering caused by the detected magnetic fluctuations.
Quantitative Dynamics: The temperature-dependent relaxation rate was fitted using a Gaussian fluctuation model, yielding a precise critical temperature T_C = 359.8 ± 1.1 K and a peak fluctuation rate Γ₀ ≈ 0.9 kHz.

Technical Specifications

Parameter	Value	Unit	Context
Material System	Tm₃Fe₅O₁₂ (TmIG) / Gd₃Ga₅O₁₂ (GGG)	N/A	High T_C magnetic insulator
TmIG Film Thickness	20	nm	Sputtered layer
TmIG Curie Temperature (T_C)	~360 (359.8 ± 1.1)	K	Determined by M-T and NV T₁ fit
TmIG Coercivity (H_c)	35	Oe	Measured at 300 K
TmIG Lattice Mismatch	-0.16	%	Relative to GGG substrate
NV Sensor Type	Shallow ¹⁴N⁺ ensemble	N/A	[111]-oriented diamond
NV Implantation Depth	~7	nm	Below diamond surface
Lateral Spatial Resolution	~360	nm	Confocal optical diffraction limit
Static Field Resolution	±0.3	µT	NV sensor, improved by averaging
Dynamic Sensitivity	~1.6	µT/sqrt(Hz)	NV ODMR system sensitivity
Peak Fluctuation Rate (Γ₀)	0.899 ± 0.026	kHz	Gaussian fit of critical dynamics
System Thermal Drift	less than 1.5	K/h	Tracked via zero-field splitting (D)

Key Methodologies

1. TmIG Thin Film Fabrication (RF Magnetron Sputtering)

Substrate: Gd₃Ga₅O₁₂ (111) single crystal.
Deposition Temperature: 700 °C (Substrate).
RF Power: 100 W.
Working Pressure: 1.5 Pa.
Gas Flow Ratio: Ar/O₂ = 4:1.
Growth Rate: Approximately 2.5 nm/min (20 nm total thickness).
Post-Processing: In situ annealing at 700 °C for 10 min to enhance crystallinity.

2. Diamond NV Sensor Preparation

Diamond Material: High-purity, single-crystal [100]-oriented diamond grown via CVD, mechanically polished to [111] orientation.
Implantation: ¹⁴N⁺ ions implanted at 5 keV energy.
Dose: 10¹³ ions/cm² (resulting in ~7 nm NV layer depth).
Annealing: 800 °C for 2 h under vacuum (5 x 10^-5 Pa) to form NV complexes.
Cleaning: Mixed acid solution (H₂SO₄:HNO₃:HClO₄, 1:1:1 by volume) at 220 °C for 2 h.

3. NV Quantum Magnetometry (ODMR and T₁ Relaxometry)

Setup: Custom confocal platform with [111]-oriented NV diamond placed in direct contact with the TmIG film.
Static Field Measurement (ODMR): Used Zeeman splitting (Δν) of the m_s = ±1 states to determine the local magnetic field projection (B_NV).
Dynamic Fluctuation Measurement (T₁ Relaxometry): Employed a π-τ-π pulse sequence to measure the NV spin relaxation rate (Γ = 1/T₁).
Noise Isolation: Net relaxation rate (ΔΓ) was calculated by subtracting the phonon-mediated relaxation rate measured at a remote reference site (Γ_r) from the probe site rate (Γ_p), isolating magnetic noise originating specifically from the TmIG film.

4. Macroscopic Characterization

Magnetometry (MPMS VSM): Measured M-H loops (300 K) and temperature-dependent magnetization (M-T) curves (Field-Cooled mode, 5 kOe).
Electrical Transport (PPMS): Measured longitudinal resistivity (ρ_xx) and Hall resistance using photolithographically defined Hall bar devices (200 µm x 20 µm).

Commercial Applications

The integration of high-T_C magnetic insulators with nanoscale quantum sensing capabilities is critical for advancing several quantum and spintronic technologies.

Application Area	Relevance to TmIG/NV Technology
High-Temperature Spintronics	TmIG’s T_C greater than room temperature enables robust, energy-efficient spintronic devices (e.g., spin-wave waveguides, spin-torque devices) suitable for industrial environments.
Magnetic Memory (MRAM)	The strong perpendicular magnetic anisotropy of TmIG is ideal for developing high-density, thermally stable magnetic random-access memory architectures.
Nanoscale Quantum Sensing	The NV platform offers noninvasive, quantitative mapping of magnetic noise and dynamic phenomena (e.g., critical fluctuations, domain wall motion) in complex magnetic heterostructures.
Fundamental Materials Research	Provides a unique tool for studying the intrinsic coupling between electron conduction and localized spin dynamics, crucial for designing new quantum materials.
Integrated Sensor Technology	The diamond NV sensor, operating at ambient temperature with submicron resolution, is a candidate for integration into micro-electromechanical systems (MEMS) for localized magnetic field detection and characterization.

View Original Abstract

Thulium iron garnet (Tm3Fe5O12, TmIG) is a promising material for next-generation spintronic and quantum technologies owing to its high Curie temperature and strong perpendicular magnetic anisotropy. However, conventional magnetometry techniques are limited by insufficient spatial resolution and sensitivity to probe local magnetic phase transitions and critical spin dynamics in thin films. In this study, we present the first quantitative investigation of local magnetic field fluctuations near the Curie temperature in TmIG thin films using nitrogen-vacancy (NV) center-based quantum sensing. By integrating optically detected magnetic resonance (ODMR) and NV spin relaxometry (T1 measurements) with macroscopic techniques such as SQUID magnetometry and Hall effect measurements, we systematically characterize both the static magnetization and dynamic spin fluctuations across the magnetic phase transition. Our results reveal a pronounced enhancement in NV spin relaxation rates near 360 K, providing direct evidence of critical spin fluctuations at the nanoscale. This work highlights the unique advantages of NV quantum sensors for investigating dynamic critical phenomena in complex magnetic systems and establishes a versatile, multimodal framework for studying local phase transition kinetics in high-temperature magnetic insulators.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi16060643

References

2024 - Acoustic higher-order topological insulators induced by orbital interactions [Crossref]
2024 - 23 Tesla high temperature superconducting pocket magnet [Crossref]
2023 - Bismuth doping enhanced tunability of strain-controlled magnetic anisotropy in epitaxial Y3Fe5O12 (111) films [Crossref]
2023 - Tremendous tunneling magnetoresistance effects based on van der Waals room-temperature ferromagnet Fe3GaTe2 with highly spin-polarized Fermi surfaces
2023 - Spin-wave optics in YIG realized by ion-beam irradiation [Crossref]
2023 - Strong on-chip microwave photon-magnon coupling using ultralow-damping epitaxial Y3Fe5O12 films at 2 K [Crossref]
2020 - Nanometer-thick yttrium iron garnet films with perpendicular anisotropy and low damping [Crossref]
2024 - Enhancement of perpendicular magnetic anisotropy in Tm3Fe5O12 (111) epitaxial films via synergistic stoichiometry and strain engineering [Crossref]
2008 - Nanoscale imaging magnetometry with diamond spins under ambient conditions [Crossref]
2021 - Synthesis and characterization of NiFe2O4 magnetic nanoparticles with different coating materials for magnetic particle imaging (MPI) [Crossref]