Development of nano magnetic resonance imaging 

 

Outline of research

In this research, a technique of diamond spin sensor is combined with scanning probe microscopy (SPM) such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM), to realize nano magnetic resonance imaging with atomic resolution. Single electron spin detection using a diamond spin; composed of single electron spin at nitrogen vacancy center (NV center) in diamond crystal, has been demonstrated. Furthermore, this single spin in diamond can be used itself as a spin sensor detecting stray magnetic field from electron spins and nuclear spins existing around diamond spin by monitoring change of magnetic resonance frequency and life time of diamond spin. The diamond sensor in shape of nano particle is attached at the apex of SPM probe with optical confocal microscope setup realizing scanning diamond spin probe microscopy. This enables us simultaneous measurement of spin sensing and atomically resolved imaging for the structures on the surfaces.

At room temperature and atmospheric condition experiment can be started immediately, and the stray fields from magnetic domain structure in the ferromagnetic thin film, accumulated spins at the interfaces between normal metal and ferromagnetic metal, and thermal magnon in magnetic sample is planned to be sensed and imaged. For the most challenging issue; ‘single nuclear spin sensing’, this scanning diamond spin probe microscopy is constructed in an ultra-high vacuum and low temperature (5 Kelvin) condition to achieve ultimate single spin sensitivity and stable atomic resolution performance. Atomically well-defined nuclear spin structure is prepared; carbon monoxide adsorbed on the surface where single nuclear spin exists in carbon-13 isotope but not in carbon-12, and ‘single nuclear spin imaging’ is performed.

 

Objectives, research plan, significance, background

(1)     Objectives and research plan

Simple objective of this research is to achieve ‘single nuclear spin magnetic resonance imaging’. Single spin magnetic resonance detection is a challenging and ultimate goal of dynamical spin sensing. From the point of view of application, achievement of single spin magnetic resonance imaging bear a ripple effects in the field of physics, chemistry, life science, and even in the medical field (as known magnetic resonance imaging (MRI) scan). Since the detection of single electron spin resonance, at nitrogen vacancy center (NV center) in diamond crystal, has been demonstrated by using optical method (Gruber et al., 1997), it has been tried to prove that this diamond spin sensor itself can be used as a spin probe by sensing stray magnetic field from electron spins and nuclear spins around. Thus, one of interesting application is to make scanning spin sensing microscopy combining this diamond sensor with a scanning probe microscopy such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM).

Lead researcher has developed core techniques and many experiences for the detection of magnetic resonance phenomena. Lead researcher developed first, novel atomic force microscopy based on quartz sensing type working at liquid 3He temperature (4K) (2003 – 2007) for the study of atomically resolved non contact AFM imaging, second, scanning microwave microscopy (2007 – 2010) for the study of magnetic resonance imaging in the magnetic material, and third started objective of this research: diamond spin probe microscopy (2010 -1013), and also studied spin wave (collective motion of spins) in magnetic materials (2010 -2013). Thus technical things and knowledge for achieving nano magnetic resonance imaging has been accumulated and the ‘nano magnetic resonance imaging’ is very best objective for the lead researcher. We planned more concrete objectives as probing, (1) spins in magnetic domain structure, (2) accumulated spins at the interfaces between normal metal and ferromagnetic metal, (3) thermal magnon in magnetic material, and (4) single nuclear spin of carbon-13 isotope in the carbon mono oxide molecule structures, that will create great impact in each fields.

 

“Plans 1”

Stray magnetic field sensing is performed at room temperature and air conditions by using diamond spin probe of which development has been already started from 2010, and sensing and imaging of spin accumulation at the interface between normal metal and magnetic material, and thermal magnon in magnetic material is achieved. At the same time construction of scanning diamond spin probe microscopy in an ultra-high vacuum and low temperature (5 Kelvin) condition, to achieve ultimate single spin sensitivity and stable atomic resolution performance, is designed and carried.

 

“Plans 2”

Variation of spin sensing materials is extending not only magnetic materials but also paramagnetic samples such as unpaired electron on the Silicon surface. Finally by finishing development of scanning diamond spin probe microscopy in an ultra-high vacuum and low temperature (5 Kelvin) condition, the single nuclear spin magnetic resonance imaging is carried out on single nuclear spins of carbon-13 isotope in the carbon mono oxide molecule structures.

 

Objective of this project is to observe magnetic resonance and image it at nanometer scale (ultimately to achieve ‘single nuclear spin magnetic resonance imaging’). This method of sensing of small number of spin’s dynamical motion can be applied into various environment, room temperature, low temperature, air condition, ultra high vacuum, liquid phase, depending on each purpose of the study. Thus, once the objective is achieved, the technique and methods can apply to the variety of fields, such as physics, (spintronics, quantum computing), chemistry (single electron spin and even single nuclear spin resonance detection at a molecule), life science (magnetic resonance detection at deoxyribonucleic acid (DNA)), and even in the medical field (as known magnetic resonance imaging (MRI) scan), and will bear a ripple effects, because this research objective “nano magnetic resonance imaging” detectable spin dynamics at nano scale provides new insight to the variety of research fields.

 

The point of this project is to construct following two different directions of experimental setup (sub project) for “nanoscale magnetic resonance imaging”.

(1) Development of easy-to-use nano magnetic resonance imaging setup working at room

temperature and air condition. To achieve sub objectives of spin sensing from magnetic domain structure in the ferromagnetic thin film, accumulated spins at the interfaces between

normal metal and ferromagnetic metal, and thermal magnon in magnetic sample can be done with this easy-to-use experimental setup. This setup has an advantage to perform experiment flexibly and suitable for to spill over the method of “nanoscale magnetic resonance imaging” to the variety of the fields, such as physics, (spintronics, quantum computing), chemistry (single electron spin and even single nuclear spin resonance detection at a molecule), life science (magnetic resonance detection at deoxyribonucleic acid (DNA)), and even in the medical field (as known magnetic resonance imaging (MRI) scan).

   (2) Development of diamond spin probe microscopy working at low temperature and ultra-high vacuum conditions for to achieve “single nuclear spin magnetic resonance imaging”. This project is an ultimate goal of magnetic resonance detection and requires high-performance of experimental setup. Lead researcher develop this setup with Co-researcher by modifying the low temperature scanning probe microscopy (belonging to Co-researchers’ laboratory, (Surface and interface Science Laboratory, Dr. You Soo Kim)), and pursue to make diamond spin probe with highest spin sensitivity and with atomic resolution.

 

(a)        Contributions this research project will make to its field, or influence it will have.

We plan to achieve following spin sensing studies; (1) magnetic domain structure in the ferromagnetic thin film, (2) accumulated spins at the interfaces between normal metal and ferromagnetic metal, (3) thermal magnon in magnetic sample, and (4) single spin magnetic resonance imaging. (1) – (3) have an impact to the field of spintronics where information of the spin diffusion length (spatial distribution of spin, and spin life time) at nanometer scales. (4) is the ultimate goal of sensing of dynamical motion of spin, and thus will have greatly a spillover effect to the field of physics, chemistry, life science and medical field (realizing nano magnetic resonance imaging (MRI) scan).

 

(b)       Necessity and urgency of this research.

The study utilizing diamond spin probe is emerging field in last few years, since it has shown its ability to sense spins existing around at nanometer scale. Furthermore this technique easily applicable to many studies because it works at room temperature and air conditions. Thus it requires urgent action to show original studies by using the diamond spin probe.

 

(c)        Necessity to promote this project.

There are many research fields, such as physics, chemistry, Bioscience, and brain science. In all the fields the scheme of magnetic resonance is used, and thus we are convinced that this research project will become a key technology to link these research fields each other stimulating interdisciplinary activities.

 

(1)     Domestic and international trends in fields related to this research project

In the international trends, diamond probe application is already getting one hot topics, and til now, single electron spin detection has been demonstrated, and for nuclear spin, latest result has shown 40,000 nuclear spin detection.

 

(2)     State of readiness

Lead researcher has been funded by the CANON foundation for the research titled “Single spin detection by the developments of diamond NV center probe magnetic resonance microscopy” and have preliminary result for the spin sensing study using diamond spin sensor. In this study diamond nanoparticle was spread on the magnetic sample (Yttrium iron garnet) where magnetic domains are formed. It is observed that depending on the position of the diamond on the magnetic domain different stray field is detected; showing possibility to image magnetic domains by using diamond spin probe (Fig. 1) (This work was done in collaboration with C. Meriles group in City College of New York, USA) . Lead researcher has prepared diamond spin probe microscopy setup working at room temperature and air condition, and thus is ready for to start experiments.