Nanometers-Thick Ferromagnetic Surface Produced by Laser Cutting of Diamond

At a Glance

Metadata	Details
Publication Date	2022-01-28
Journal	Materials
Authors	A. Setzer, P. Esquinazi, С.Г. Буга, M. Georgieva, T. Reinert
Institutions	Leipzig University, Technological Institute for Superhard and Novel Carbon Materials
Citations	5
Analysis	Full AI Review Included

Technical Documentation & Analysis: Nanometers-Thick Ferromagnetic Surface Produced by Laser Cutting of Diamond

Executive Summary

This research demonstrates a novel, non-doping method for inducing robust, room-temperature ferromagnetism (RT-FM) on diamond surfaces using standard nanosecond laser cutting techniques.

Core Achievement: A thin, graphitic-like layer (estimated thickness ≤20 nm) exhibiting stable ferromagnetism at 300 K was successfully created on both natural and CVD diamond crystals via 532 nm laser processing.
Orientation Dependence: The ferromagnetic response is critically dependent on crystal orientation, showing a robust signal only on the (100) surface, while being significantly weaker or negligible on (110) and (111) surfaces.
Mechanism: The RT-FM is attributed to the disordered, defect-rich graphitic layer formed by the laser-induced thermal modification, not to magnetic impurities (which were quantified below 2.6 ppm).
Reversibility: The magnetic signal was successfully eliminated by standard post-processing techniques, including chemical etching (strong oxidizing acids at 120 °C) and moderate thermal annealing (T < 650 °C).
Application Potential: This technique provides a scalable method for creating localized magnetic spots (using a 15 µm focus spot) on diamond, opening pathways for novel memory devices and influencing the magneto-optical response of quantum defects like NV-centers.

Technical Specifications

The following hard data points were extracted from the experimental methodology and results:

Parameter	Value	Unit	Context
Laser Wavelength	532	nm	Cutting/Graphitization
Laser Pulse Duration	200	ns	Cutting/Graphitization
Laser Energy Density	300	J/cm²	Cutting/Graphitization
Laser Focus Spot Diameter	15	µm	Localized modification area
Ferromagnetic Layer Thickness	≤20	nm	Estimated maximum thickness of magnetic layer
Saturation Magnetization (M_s)	10 to 20	emu/g	Calculated for the 20 nm layer at 300 K
Observed Ferromagnetic Temperature	300	K	Room Temperature (RT-FM)
Estimated Curie Temperature (T_c)	500 to 750	K	Extrapolated from temperature dependence
Maximum Magnetic Impurity (Fe)	2.6	µg/g (ppm)	Measured via PIXE in sample 164
CVD Sample N Concentration	≤10	ppm	Used for orientation study
Graphite Removal Method 1	Chemical Etching (H₂SO₄/HNO₃/HClO₄)	120 °C	Removal of graphitic layer
Graphite Removal Method 2	Thermal Annealing	<650 °C	Removal of graphitic layer

Key Methodologies

The experiment focused on controlled laser modification and subsequent magnetic characterization of high-quality diamond crystals.

Sample Selection and Orientation:
- Used both natural and high-purity CVD diamond crystals.
- CVD samples featured low N concentration (≤10 ppm) and low magnetic impurities (<2 ppm).
- Samples were precisely oriented to expose (100), (110), and (111) surfaces for laser cutting.
Laser Treatment (Graphitization):
- A 532 nm laser with 200 ns pulse duration and 300 J/cm² energy density was used.
- The laser beam was focused to a 15 µm spot and moved along the cut line, inducing localized heating and graphitization of the diamond surface.
Post-Treatment (Graphite Removal):
- Chemical Etching: Samples were treated with a strong oxidizing acid mixture (H₂SO₄, HNO₃, HClO₄) heated to 120 °C for 4 hours to remove the graphitic layer (estimated removal depth ~20 nm).
- Thermal Annealing: Samples were annealed in air at temperatures below 650 °C to confirm the thermal instability of the magnetic layer.
Structural and Impurity Characterization:
- Raman Spectroscopy: Confirmed the formation of disordered graphite-like peaks (G-band at 1580 cm^-1 and D-band at 1350 cm^-1) on the laser-cut surfaces.
- PIXE (Particle-Induced X-ray Emission): Used 2.0 MeV protons to quantify magnetic impurities (Fe, Co, Ni) down to minimum detectable limits (MDL) of 0.03-0.08 µg/g.
Magnetic Characterization:
- Measurements were performed using a SQUID magnetometer.
- Magnetic field loops and temperature hysteresis (Field-Cooled, FC, and Zero-Field-Cooled, ZFC) were obtained at 300 K and below, confirming the robust ferromagnetic signal on (100)-cut surfaces.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-quality, precisely oriented diamond substrates for advanced material modification and quantum applications. 6CCVD is uniquely positioned to supply the necessary materials and custom processing services to replicate and extend this work, particularly in creating integrated magnetic/quantum devices.

Applicable Materials

To replicate the robust, orientation-dependent ferromagnetism observed in this study, researchers require high-purity, low-defect diamond.

Optical Grade Single Crystal Diamond (SCD): Essential for studies requiring ultra-low background noise and precise crystal orientation control. Our SCD material features extremely low nitrogen (N < 1 ppm) and minimal magnetic impurities, ensuring that observed magnetism is truly defect-induced, not impurity-driven.
Custom Oriented Substrates: 6CCVD provides SCD wafers with precise (100), (110), and (111) orientations, allowing researchers to systematically investigate the observed orientation dependence of graphitization and ferromagnetism.

Customization Potential

The paper emphasizes creating localized magnetic spots (15 µm focus) and the need for post-treatment (etching/annealing). 6CCVD offers comprehensive services to support these complex fabrication steps.

Research Requirement/Challenge	6CCVD Solution & Capability	Technical Advantage
Precise Laser Modification	Custom Laser Cutting & Patterning Services.	We can pre-pattern or laser-cut substrates to specific geometries, or assist in developing localized modification recipes, crucial for creating the 15 µm magnetic spots described.
Surface Quality for Quantum Integration	Ultra-Smooth Polishing.	SCD substrates are polished to an atomic finish (Ra < 1 nm), ideal for subsequent thin-film deposition or integration with quantum emitters (e.g., NV-centers).
Device Integration & Contacts	Internal Custom Metalization.	The integration of localized magnetic spots into functional devices often requires electrical contacts. 6CCVD offers in-house deposition of critical metals, including Ti, Pt, Au, Pd, W, and Cu, tailored to specific device architectures.
Scaling and Large Area Studies	Large-Format PCD Wafers.	For scaling up applications like memory arrays, we offer Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter, polished to Ra < 5 nm.
Substrate Dimensions	Custom Thicknesses and Dimensions.	We supply SCD and PCD layers from 0.1 µm to 500 µm, and robust substrates up to 10 mm thick, supporting both thin-film studies and bulk thermal management requirements.

Engineering Support

The successful creation of defect-induced ferromagnetism requires expert control over material purity, orientation, and post-processing. 6CCVD’s in-house PhD team specializes in MPCVD diamond growth and characterization. We can assist researchers in:

Material Selection: Choosing the optimal SCD grade and orientation for similar defect-induced magnetism (DIM) or NV-center manipulation projects.
Process Optimization: Consulting on post-growth treatments, including chemical etching protocols and thermal annealing parameters, to control the graphitic layer thickness and magnetic properties.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

In this work, we demonstrate that cutting diamond crystals with a laser (532 nm wavelength, 0.5 mJ energy, 200 ns pulse duration at 15 kHz) produced a ≲20 nm thick surface layer with magnetic order at room temperature. We measured the magnetic moment of five natural and six CVD diamond crystals of different sizes, nitrogen contents and surface orientations with a SQUID magnetometer. A robust ferromagnetic response at 300 K was observed only for crystals that were cut with the laser along the (100) surface orientation. The magnetic signals were much weaker for the (110) and negligible for the (111) orientations. We attribute the magnetic order to the disordered graphite layer produced by the laser at the diamond surface. The ferromagnetic signal vanished after chemical etching or after moderate temperature annealing. The obtained results indicate that laser treatment of diamond may pave the way to create ferromagnetic spots at its surface.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma15031014

References

2005 - Irradiation-induced magnetism in carbon nanostructures [Crossref]
2017 - Superconducting Ferromagnetic Nanodiamond [Crossref]
2015 - Novel phase of carbon, ferromagnetism, and conversion into diamond [Crossref]
2004 - Materials Design of Ferromagnetic Diamond [Crossref]
2004 - Magnetic properties of polymerized C60: The influence of defects and hydrogen [Crossref]
2006 - Edge state on hydrogen-terminated graphite edges investigated by scanning tunneling microscopy [Crossref]
2005 - Hydrogen-induced magnetism in carbon nanotubes [Crossref]
2005 - Hydrogen-induced magnetism in carbon nanotubes [Crossref]
2005 - Magnetic Moment in Proton-Irradiated Graphite