arXiv subjects

Manh-Huong Phan

Publications and source records attributed to Manh-Huong Phan.

At least 19 recordsLinked to original sources

arXiv2026

Ultra-Stable Weyl Topology Driven by Magnetic Textures in the Shandite Compound Co3Sn2S(2-x)Sex

We employ state-of-the-art first-principles calculations to investigate the shandite compounds Co3Sn2S2, Co3Sn2SeS, and Co3Sn2Se2, which host Weyl fermions and complex magnetic textures. Their magnetic structures are governed primarily by exchange interactions and magnetocrystalline anisotropy, whereas the symmetry-allowed alternating-layer Dzyaloshinskii-Moriya interaction (DMI) is found to be negligible. We identify a previously unrecognized spin-chiral interaction (SCI) arising from the kagome lattice topology, which plays a decisive role in stabilizing the experimentally observed magnetic textures. The extracted magnetic parameters reproduce experimental trends, with the SCI emerging as a novel and dominant contribution. The calculated SCI strengths are 0.78 meV, 0.86 meV, and 0.87 meV for Co3Sn2S2, Co3Sn2SeS, and Co3Sn2Se2, respectively. Furthermore, we demonstrate that short-wavelength magnetic textures drive phase transitions of the Weyl nodes, resulting in band flattening and the opening of an emergent gap. This newly identified SCI, together with the associated electronically driven phase transitions, provides a promising route for manipulating transport properties in spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Single-Spin Nitrogen-Vacancy Magnetometer with Enhanced Static Field Sensitivity

Precision sensing and imaging of weak static magnetic fields are crucial for a variety of emerging nanoscale applications. While nitrogen-vacancy (NV) centers in diamond provide exceptional AC magnetic field sensitivity with nanoscale spatial resolution, their sensitivity to static (DC) magnetic fields is fundamentally limited by the short dephasing time (T2*) due to spin-spin interactions. In this work, we present a novel hybrid sensing approach that integrates a soft ferromagnetic microwire with a single near-surface NV center to amplify its response to external static magnetic fields. This hybrid configuration achieves a DC magnetic field sensitivity of 63 nT/sqrt(Hz) for a single NV center - about 500 times greater than conventional inhomogeneous broadening- or T2*-limited magnetometry, with potential for further enhancement. The compact and highly sensitive nature of this sensor opens new opportunities for quantum sensing applications involving the detection of static or slowly varying magnetic fields across diverse scientific and technological domains.

quant-ph↗

arXiv2025

Low-dimensional magnetocaloric materials for energy-efficient magnetic refrigeration: Does size matter?

The magnetocaloric effect (MCE) provides a promising foundation for the development of solid-state refrigeration technologies that could replace conventional gas compression-based cooling systems. Current research efforts primarily focus on identifying cost-effective magnetic materials that exhibit large MCEs under low magnetic fields across broad temperature ranges, thereby enhancing cooling efficiency. However, practical implementation of magnetic refrigeration requires more than bulk materials; real-world devices demand efficient thermal management and compact, scalable architectures, often achieved through laminate designs or miniaturized geometries. Magnetocaloric materials with reduced dimensionality, such as ribbons, thin films, microwires, and nanostructures, offer distinct advantages, including improved heat exchange, mechanical flexibility, and integration potential. Despite these benefits, a comprehensive understanding of how size, geometry, interfacial effects, strain, and surface phenomena influence the MCE remains limited. This review aims to address these knowledge gaps and provide guidance for the rational design and engineering of magnetocaloric materials tailored for high-performance, energy-efficient magnetic refrigeration systems.

physics.app-ph↗

arXiv2025

Slow ferromagnetic fluctuations in the kagome metal Sc$_3$Mn$_3$Al$_7$Si$_5$ revealed by $^{27}$Al NMR

Static and dynamical magnetic and electronic properties of the kagome metal Sc$_3$Mn$_3$Al$_7$Si$_5$ have been investigated by $^{27}$Al nuclear magnetic resonance (NMR) measurements. The temperature dependence of Knight shift ($K$) shows a similar temperature dependence of the DC magnetic susceptibility $χ$ except for the low-temperature region below $\sim$ 50 K where $K$ is almost constant while $χ$ keeps increasing, which suggests that the increase in $χ$ at low temperatures is not intrinsic. $^{27}$Al spin-lattice relaxation rate divided by temperature ($1/T_1T$) is found to be constant, confirming the metallic state of Sc$_3$Mn$_3$Al$_7$Si$_5$ from a microscopic point of view. Based on a Korringa ratio analysis using the $T_1$ and $K$ data, ferromagnetic spin fluctuations are found to dominate in Sc$_3$Mn$_3$Al$_7$Si$_5$. These fluctuations are suggested to be very slow with frequencies on the order of kilohertz or lower.

cond-mat.str-el↗

arXiv2025

Interface Magnetism in Vanadium-doped MoS$_2$/Graphene Heterostructures

Magnetism in two-dimensional materials is of great importance in discovering new physical phenomena and developing new devices at the nanoscale. In this paper, first-principles simulations are used to calculate the electronic and magnetic properties of heterostructures composed of Graphene and MoS$_2$ considering the influence of point defects and Vanadium doping. It is found that the concentration of the dopants and the types of defects can result in induced magnetic moments leading to ferromagnetically polarized systems with sharp interfaces. This provides a framework for interpreting the experimental observations of enhanced ferromagnetism in both MoS$_2$/Graphene and V-doped MoS$_2$/Graphene heterostructures. The computed electronic and spin polarizations give a microscopic understanding of the origin of ferromagnetism in these systems and illustrate how doping and defect engineering can lead to targeted property tunability. Our work has demonstrated that through defects engineering, ferromagnetism can be achieved in V-doped MoS$_2$/Graphene heterostructures, providing a potential way to induce magnetization in other TMDC/Graphene materials and opening new opportunities for their applications in nano-spintronics.

cond-mat.mtrl-sci↗

arXiv2024

Superparamagnetic Superparticles for Magnetic Hyperthermia Therapy: Overcoming the Particle Size Limit

Iron oxide (e.g., Fe$_3$O$_4$ or Fe$_2$O$_3$) nanoparticles are promising candidates for a variety of biomedical applications ranging from magnetic hyperthermia therapy to drug delivery and bio-detection, due to their superparamagnetism, non-toxicity, and biodegradability. While particles of small size (below a critical size, ~20 nm) display superparamagnetic behavior at room temperature, these particles tend to penetrate highly sensitive areas of the body such as the Blood-Brain Barrier (BBB), leading to undesired effects. In addition, these particles possess a high probability of retention, which can lead to genotoxicity and biochemical toxicity. Increasing particle size is a means for addressing these problems but also suppresses the superparamagnetism. We have overcome this particle size limit by synthesizing unique polycrystalline iron oxide nanoparticles composed of multiple nanocrystals of 10 to 15 nm size while tuning particle size from 160 to 400 nm. These so-called superparticles preserve superparamagnetic characteristics and exhibit excellent hyperthermia responses. The specific absorption rates (SAR) exceed 250 W/g (HAC = 800 Oe, f = 310 kHz) at a low concentration of 0.5 mg/mL, indicating their capability in cancer treatment with minimum dose. Our study underscores the potential of size-tunable polycrystalline iron oxide superparticles with superparamagnetic properties for advanced biomedical applications and sensing technologies.

physics.app-ph↗

arXiv2024

The Discovery of Giant Positive Magnetoresistance in Proximity to Helimagnetic Order in Manganese Phosphide Nanostructured Films

The study of magnetoresistance (MR) phenomena has been pivotal in advancing magnetic sensors and spintronic devices. Helimagnets present an intriguing avenue for spintronics research. Theoretical predictions suggest that MR magnitude in the helimagnetic (HM) regime surpasses that in the ferromagnetic (FM) regime by over an order of magnitude. However, in metallic helimagnets like manganese phosphide, MR in the HM phase remains modest (10%), limiting its application in MR devices. Here, a groundbreaking approach is presented to achieve a giant low field MR effect in nanostructured manganese phosphide films by leveraging confinement and strain effects along with spin helicity. Unlike the modest MR observed in bulk manganese phosphide single crystals and large grain polycrystalline films, which exhibit a small negative MR in the FM region (2%) increasing to 8% in the HM region across 10-300 K, a grain size-dependent giant positive MR (90%) is discovered near FM to HM transition temperature (110 K), followed by a rapid decline to a negative MR below 55 K in manganese phosphide nanocrystalline films. These findings illuminate a novel strain-mediated spin helicity phenomenon in nanostructured helimagnets, presenting a promising pathway for the development of high-performance MR sensors and spintronic devices through the strategic utilization of confinement and strain effects.

physics.app-ph↗

arXiv2024

Temperature Evolution of Magnon Propagation Length in Tm$_3$Fe$_5$O$_{12}$ Thin Films: Roles of Magnetic Anisotropy and Gilbert Damping

The magnon propagation length ($\langleξ\rangle$) of a ferro/ferrimagnet (FM) is one of the key factors that controls the generation and propagation of thermally-driven spin current in FM/heavy metal (HM) bilayer based spincaloritronic devices. Theory predicts that for the FM layer, $\langleξ\rangle$ is inversely proportional to the Gilbert damping ($α$) and the square root of the effective magnetic anisotropy constant ($K_{\rm eff}$). However, direct experimental evidence of this relationship is lacking. To experimentally confirm this prediction, we employ a combination of longitudinal spin Seebeck effect (LSSE), transverse susceptibility, and ferromagnetic resonance experiments to investigate the temperature evolution of $\langleξ\rangle$ and establish its correlation with the effective magnetic anisotropy field, $H_K^{\rm eff}$ ($\propto K_{\rm eff}$) and $α$ in Tm$_3$Fe$_5$O$_{12}$ (TmIG)/Pt bilayers. We observe concurrent drops in the LSSE voltage and $\langleξ\rangle$ below 200$^\circ$K in TmIG/Pt bilayers regardless of TmIG film thickness and substrate choice and attribute it to the noticeable increases in $H_K^{\rm eff}$ and $α$ that occur within the same temperature range. From the TmIG thickness dependence of the LSSE voltage, we determined the temperature dependence of $\langleξ\rangle$ and highlighted its correlation with the temperature-dependent $H_K^{\rm eff}$ and $α$ in TmIG/Pt bilayers, which will be beneficial for the development of rare-earth iron garnet-based efficient spincaloritronic nanodevices.

cond-mat.mtrl-sci↗

arXiv2024

Tailoring magnetic and hyperthermia properties of biphase iron oxide nanocubes through post-annealing

Tailoring the magnetic properties of iron oxide nanosystems is essential to expand their biomedical applications. In this study, the 34 nm iron oxide nanocubes with two phases consisting of Fe3O4 and alpha-Fe2O3 were annealed for 2 hours in the presence of O2, N2, He, and Ar to tune the respective phase volume fractions and control the magnetic properties. X-ray diffraction and magnetic measurements were carried out post-treatment to evaluate the changes of the treated samples compared to the as-prepared, which showed an enhancement of the alpha-Fe2O3 phase in the samples annealed with O2, while the others indicated Fe3O4 enhancement. Furthermore, the latter samples indicated enhancements in the crystallinity and saturation magnetization while coercivity enhancement was most significant in the samples annealed with O2, resulting in the highest specific absorption rates (up to 1000 W/g) in all the applied fields of 800, 600, and 400 Oe in agar during magnetic hyperthermia measurements. The general enhancement in the specific absorption rate post-annealing underscores the importance of the annealing atmosphere in the enhancement of the magnetic and structural properties of nanostructures.

cond-mat.mtrl-sci↗

arXiv2024

Vanadium-Doped Molybdenum Disulfide Monolayers with Tunable Electronic and Magnetic Properties: Do Vanadium-Vacancy Pairs Matter?

Monolayers of molybdenum disulfide (MoS2) are the most studied two-dimensional (2D) transition-metal dichalcogenides (TMDs), due to its exceptional optical, electronic, and opto-electronic properties. Recent studies have shown the possibility of incorporating a small amount of magnetic transition metals (e.g., Fe, Co, Mn, V) into MoS2 to form a 2D dilute magnetic semiconductor (2D-DMS). However, the origin of the observed ferromagnetism has remained elusive, due to the presence of randomly generated sulfur vacancies during synthesis that can pair with magnetic dopants to form complex dopant-vacancy configurations altering the magnetic order induced by the dopants. By combining high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging with first-principles density functional theory (DFT) calculations and magnetometry data, we demonstrate the critical effects of sulfur vacancies and their pairings with vanadium atoms on the magnetic ordering in V-doped MoS2 (V-MoS2) monolayers. Additionally, we fabricated a series of field effect transistors on these V-MoS2 monolayers and observed the emergence of p-type behavior as the vanadium concentration increased. Our study sheds light on the origin of ferromagnetism in V-MoS2 monolayers and provides a foundation for future research on defect engineering to tune the electronic and magnetic properties of atomically thin TMD-based DMSs.

cond-mat.mtrl-sci↗

arXiv2023

Coupling of structure and magnetism to spin splitting in hybrid organic-inorganic perovskites

Hybrid organic-inorganic perovskites are famous for the diversity of their chemical compositions, phases and phase transitions, and associated physical properties. We use a combination of experimental and computational techniques to reveal strong coupling between structure, magnetism, and spin splitting in a representative of the largest family of hybrid organic-inorganic perovskites: the formates. With the help of first-principles simulations, we find spin splitting in both conduction and valence bands of [NH$_2$NH$_3$]Co(HCOO)$_3$, induced by spin-orbit interactions, which can reach up to 14~meV. Our magnetic measurements reveal that this material exhibits canted antiferromagnetism below 15.5 K. The direction of the associated antiferromagnetic order parameter is strongly coupled with the spin splitting already in the centrosymmetric phase, allowing for the creation and annihilation of spin splitting through the application of a magnetic field. Furthermore, the structural phase transition into experimentally observed polar Pna2$_1$ phase completely changes the aforementioned spin splitting and its coupling to magnetic degrees of freedom. This reveals that in [NH$_2$NH$_3$]Co(HCOO)$_3$, the structure and magnetism are strongly coupled to spin splitting in a way that allows for its manipulation through both magnetic and electric fields. As an example, for a given point inside the Brillouin zone of centrosymmetric Pnma phase of [NH$_2$NH$_3$]Co(HCOO)$_3$, spin splitting can be turned on/off by aligning the antiferromagnetic vector along certain crystallographic directions or through inducing a polar phase by the application of an electric field. We believe that our findings offer an important step toward fundamental understanding and practical applications of materials with coupled properties.

cond-mat.mtrl-sci↗

arXiv2023

Giant magnetocaloric effect and hysteresis loss in Mn$_x$Fe$_{2-x}$P$_{0.5}$Si$_{0.5}$ ($x$ = 0.7-1.2) microwires at ambient temperatures

Magnetocaloric microwires are very promising for energy-efficient magnetic refrigeration in micro electromechanical systems (MEMS) and nano electromechanical systems (NEMS). Creating microwires that exhibit large magnetocaloric effects around room temperature represents an important but challenging task. Here, we report a tunable giant magnetocaloric effect around room temperature in Mn$_x$Fe$_{2-x}$P$_{0.5}$Si$_{0.5}$ ($x$ = 0.7-1.2) microwires by utilizing a melt-extraction technique paired with thermal treatment and chemical engineering. The isothermal magnetic entropy change DeltaSiso and Curie temperature (TC) can be tuned by adjusting the Mn/Fe ratio. The TC varies from 351 to 190 K as x increases from 0.8 to 1.2. Among the compositions investigated, the x = 0.9 sample shows the largest value of DeltaSiso = 18.3 J kg$^{-1}$ K$^{-1}$ for a field change of 5 T around 300 K. After subtracting magnetic hysteresis loss, a large refrigerant capacity of ~284.6 J kg$^{-1}$ is achieved. Our study paves a new pathway for the design of novel magnetocaloric microwires for active magnetic refrigeration at ambient temperatures.

physics.app-ph↗

arXiv2023

Advanced magnetocaloric microwires: What does the future hold?

Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) is a promising alternative to conventional vapor compression refrigeration techniques. The cooling efficiency of a magnetic refrigerator depends on its refrigeration capacity and operation frequency. Existing refrigerators possess limited cooling efficiency due to the low operating frequency (around tens of Hz). Theory predicts that reducing geometrical effects can increase the operation frequency by reducing the relaxation time of a magnetic material. As compared to other shapes, magnetocaloric wires transfer heat most effectively to a surrounding environment, due to their enhanced surface area. The wire shape also yields a good mechanical response, reducing the relaxation time and consequently increasing the operation frequency of the cooling device. Experiments have validated the theoretical predictions. By assembling microwires with different magnetocaloric properties and Curie temperatures into a laminate structure, a table-like magnetocaloric bed can be created and used as an active cooling device for micro-electro-mechanical system (MEMS) and nano-electro-mechanical system (NEMS). This paper assesses recent progress in the development of magnetocaloric microwires and sheds light on the important factors affecting the magnetocaloric behavior and cooling efficiency in microwire systems. Challenges, opportunities, and strategies regarding the development of advanced magnetocaloric microwires are also discussed.

physics.app-ph↗

arXiv2023

Real-Time Magnetic Tracking and Diagnosis of COVID-19 via Machine Learning

The COVID-19 pandemic underscored the importance of reliable, noninvasive diagnostic tools for robust public health interventions. In this work, we fused magnetic respiratory sensing technology (MRST) with machine learning (ML) to create a diagnostic platform for real-time tracking and diagnosis of COVID-19 and other respiratory diseases. The MRST precisely captures breathing patterns through three specific breath testing protocols: normal breath, holding breath, and deep breath. We collected breath data from both COVID-19 patients and healthy subjects in Vietnam using this platform, which then served to train and validate ML models. Our evaluation encompassed multiple ML algorithms, including support vector machines and deep learning models, assessing their ability to diagnose COVID-19. Our multi-model validation methodology ensures a thorough comparison and grants the adaptability to select the most optimal model, striking a balance between diagnostic precision with model interpretability. The findings highlight the exceptional potential of our diagnostic tool in pinpointing respiratory anomalies, achieving over 90% accuracy. This innovative sensor technology can be seamlessly integrated into healthcare settings for patient monitoring, marking a significant enhancement for the healthcare infrastructure.

cs.LG↗

arXiv2023

Large thermo-spin effects in Heusler alloy based spin-gapless semiconductor thin films

Recently, Heusler alloys-based spin gapless semiconductors (SGSs) with high Curie temperature (TC) and sizeable spin polarization have emerged as potential candidates for tunable spintronic applications. We report comprehensive investigation of the temperature dependent ANE and intrinsic longitudinal spin Seebeck effect (LSSE) in CoFeCrGa thin films grown on MgO substrates. Our findings show the anomalous Nernst coefficient for the MgO/CoFeCrGa (95 nm) film is $\cong 1.86$ micro V/K at room temperature which is nearly two orders of magnitude higher than that of the bulk polycrystalline sample of CoFeCrGa (= 0.018 micro V/K) but comparable to that of the magnetic Weyl semimetal Co2MnGa thin film (2-3 micro V/K). Furthermore, the LSSE coefficient for our MgO/CoFeCrGa(95nm)/Pt(5nm) heterostructure is $\cong 20.5$ $μ$V/K/$Ω$ at room temperature which is twice larger than that of the half-metallic ferromagnetic La$_{0.7}$Sr$_{0.3}$MnO$_3$ thin films ($\cong$ 20.5 $μ$V/K/$Ω$). We show that both ANE and LSSE coefficients follow identical temperature dependences and exhibit a maximum at $\cong$ 225 K which is understood as the combined effects of inelastic magnon scatterings and reduced magnon population at low temperatures. Our analyses not only indicate that the extrinsic skew scattering is the dominating mechanism for ANE in these films but also provide critical insights into the functional form of the observed temperature dependent LSSE at low temperatures. Furthermore, by employing radio frequency transverse susceptibility and broadband ferromagnetic resonance in combination with the LSSE measurements, we establish a correlation among the observed LSSE signal, magnetic anisotropy and Gilbert damping of the CoFeCrGa thin films, which will be beneficial for fabricating tunable and highly efficient Heusler alloys based spincaloritronic nanodevices.

physics.app-ph↗

arXiv2023

Effect of AC current annealing on the microstructure, magnetism and magnetoimpedance of CoFeSiBNb$_3$ microfibers

This paper systematically studies the changes in the microstructure and magnetic properties of CoFeSiBNb$_3$ metallic microfibers before and after AC annealing. The influence of current intensity on the magneto-impedance (MI) effect of the microfibers was analyzed and the microstructure changes of the microfibers before and after annealing were explored by means of high-resolution transmission electron microscopy. Using this data, the mechanism of current annealing to improve the MI characteristics was further revealed. The results show that the surface of the CoFeSiBNb$_3$ metallic microfibers after AC current annealing is smooth and continuous; its general magnetic properties and MI ratio increase at first with current intensity and then decrease at higher intensities. During the current annealing process, Joule heat eliminates residual stresses in the microfibers while forming atomically ordered micro-domains, which improves the degree of its organizational order. Meanwhile, a stable toroidal magnetic field is generated, which promotes the distribution of the magnetic domain structure of the microfibers, thereby improving the MI effect.

physics.app-ph↗

arXiv2023

Competing Magnetic Interactions and Field-Induced Metamagnetic Transition in Highly Crystalline Phase-Tunable Iron Oxide Nanorods

The inherent existence of multi phases in iron oxide nanostructures highlights the significance of them being investigated deliberately to understand and possibly control the phases. Here, the effects of annealing at 250 0C with a variable duration on the bulk magnetic and structural properties of high aspect ratio bi-phase iron oxide nanorods with ferrimagnetic Fe3O4 and antiferromagnetic alpha-Fe2O3 is explored. Increasing annealing time under a free flow of oxygen enhanced the alpha-Fe2O3 volume fraction, and improved the crystallinity of the Fe3O4 phase, identified in changes in the magnetization as a function of annealing time. A critical annealing time of approximately 3 hours maximized the presence of both phases, as observed via an enhancement in the magnetization and an interfacial pinning effect. This is attributed to disordered spins separating the magnetically distinct phases which tend to align with the application of a magnetic field at high temperatures. The increased antiferromagnetic phase can be distinguished due to the field-induced metamagnetic transitions observed in structures annealed for more than 3 hours and was especially prominent in the 9-hour annealed sample. Our controlled study in determining the changes in volume fractions with annealing time will enable precise control over phase tunability in iron oxide nanorods, allowing custom-made phase volume fractions in different applications ranging from spintronics to biomedical applications.

physics.app-ph↗

arXiv2023

New Research Trends in Electrically Tunable 2D van der Waals Magnetic Materials

The recent discovery of two-dimensional (2D) van der Waals (vdW) magnetic materials has provided new, unprecedented opportunities for both fundamental science and technological applications. Unlike three-dimensional (3D) magnetic systems, the electric manipulation of vdW magnetism (e.g., magnetization state, magnetic anisotropy, magnetic ordering temperature) down to the monolayer limit at ambient conditions enables high efficiency operation and low energy consumption, which has the potential to revolutionize the fields of spintronics, spin-caloritronics, and valleytronics. This article provides an in-depth analysis of the recent progress, emerging opportunities, and technical challenges in the electric manipulation of magnetic functionalities of a wide variety of 2D vdW magnetic systems ranging from metals to semiconductors and heterostructures. The state-of-the-art understanding of the mechanisms behind the electric modulation of magnetism in these 2D vdW magnetic systems will drive future research towards novel applications in spintronics, spin-caloritronics, valleytronics, and quantum computation.

cond-mat.mtrl-sci↗