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Article: Measurement of the Dzyaloshinskii-Moriya Interaction in Mn

Zhou, Wei / Ma, Chung Ting / Poon, S Joseph

2023 Volume 13, Issue 10

Abstract: ... ...

Abstract	Mn
Language	English
Publishing date	2023-05-18
Publishing country	Switzerland
Document type	Journal Article
ZDB-ID	2662255-5
ISSN	2079-4991
ISSN	2079-4991
DOI	10.3390/nano13101672
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Ultrafast switching in synthetic antiferromagnet with bilayer rare-earth transition-metal ferrimagnets.

Ma, Chung Ting / Zhou, Wei / Poon, S Joseph

Scientific reports

2022 Volume 12, Issue 1, Page(s) 19945

Abstract: In spintronics, it is important to be able to manipulate magnetization rapidly and reliably. Several methods can control magnetization, such as by applying current pulses or magnetic fields. An applied current can reverse magnetization with nanosecond ... ...

Abstract	In spintronics, it is important to be able to manipulate magnetization rapidly and reliably. Several methods can control magnetization, such as by applying current pulses or magnetic fields. An applied current can reverse magnetization with nanosecond speed through the spin torque effect. For faster switching, subpicosecond switching with femtoseconds laser pulse has been achieved in amorphous rare-earth transition-metal ferrimagnets. In this study, we employed atomistic simulations to investigate ultrafast switching in a synthetic antiferromagnet with bilayer amorphous FeGd ferrimagnets. Using a two-temperature model, we demonstrated ultrafast switching in this synthetic antiferromagnet without external magnetic fields. Furthermore, we showed that if we initially stabilize a skyrmion in this heterostructure, the ultrafast laser can switch the skyrmion state using the same mechanism. Furthermore, this bilayer design allows the control of each ferrimagnetic layer individually and opens the possibility for a magnetic tunnel junction.
Language	English
Publishing date	2022-11-19
Publishing country	England
Document type	Journal Article
ZDB-ID	2615211-3
ISSN	2045-2322 ; 2045-2322
ISSN (online)	2045-2322
ISSN	2045-2322
DOI	10.1038/s41598-022-24234-1
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Book ; Online: Half-Heusler Compounds

Poon, S. Joseph

Promising Materials For Mid-To-High Temperature Thermoelectric Conversion

2019

Abstract: Half-Heusler compounds (space group Fm3m) has garnered increasing attention in recent years in the thermoelectric community. Three decades ago, refractory RNiSn half-Heusler compounds (R represents refractory metals such as Hf, Zr, Ti) were found to be ... ...

Abstract	Half-Heusler compounds (space group Fm3m) has garnered increasing attention in recent years in the thermoelectric community. Three decades ago, refractory RNiSn half-Heusler compounds (R represents refractory metals such as Hf, Zr, Ti) were found to be narrow-gap semiconductors with large Seebeck coefficients in 100s of micro-volt per Kelvin. Today, half-Heusler (HH) compounds have emerged as promising thermoelectric materials in the intermediate temperature range (400-800oC). HH materials are endowed with good thermal stability and scalability. Thermoelectric n-p modules based on HH materials demonstrate conversion efficiency near 10% and power density output near 9 W/cm2. The objective of this article is to present a historical account of the research and development of thermoelectric half-Heusler compounds. Particularly, there have been notable achievements since 2012 thanks to the emergence of new approaches. As a result, ZT has risen from ~1 to 1.5. The various advances made since the early 1990s to the present are recounted by categorizing half-Heusler materials into three generations (Gen): Gen-1 Gen-2, and Gen-3 HH materials.
Keywords	Condensed Matter - Materials Science ; Condensed Matter - Mesoscale and Nanoscale Physics
Subject code	540
Publishing date	2019-05-09
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Measurement of the Dzyaloshinskii-Moriya Interaction in Mn4N Films that Host Skyrmions

Zhou, Wei / Ma, Chung Ting / Poon, S. Joseph

2023

Abstract: Mn4N thin film is one of the potential magnetic mediums for spintronic devices due to its ferrimagnetism with low magnetization, large perpendicular magnetic anisotropy (PMA), thermal stability, and large domain wall velocity. A recent experiment ... ...

Abstract	Mn4N thin film is one of the potential magnetic mediums for spintronic devices due to its ferrimagnetism with low magnetization, large perpendicular magnetic anisotropy (PMA), thermal stability, and large domain wall velocity. A recent experiment confirmed the existence of tunable magnetic skyrmions in MgO/Mn4N/CuxPt1-x(x=0,0.5,0.9,0.95), and density functional theory (DFT) calculation provided a large theoretical value of the interfacial Dzyaloshinskii-Moriya Interaction (iDMI) of Mn4N/Pt, which is consistent with the predicted chemical trend of DMI in transition metal/Pt films. So far, measured DMI has not been reported in Mn4N which is needed in order to support the predicted large DMI value. This paper reports the average DMI of MgO/Mn4N(17nm)/CuxPt1-x(3nm), extracted from the anomalous Hall effect with various tilted angles, based on magnetic droplet theory with DMI effects. The DMI decreases from 0.267 mJ/m2 to 0.011 mJ/m2 with non-linear tendencies as Cu concentration in the CuxPt1-x capping layer increases from 0 to 1, demonstrating the control of DMI through CuxPt1-x capping layer. Furthermore, a solid solution model is developed, based on X-ray photoelectron spectroscopy (XPS) compositional depth profile, to analyze the possible effects on DMI from the mixing layers at the surface of Mn4N. After taking into account the mixing layers, the large DMI in Mn4N film with Pt capping is consistent with the predicted DMI. Comment: 13 pages, 5 figures
Keywords	Condensed Matter - Materials Science
Subject code	530
Publishing date	2023-05-15
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Machine Learning-Based Classification, Interpretation, and Prediction of High-Entropy-Alloy Intermetallic Phases

Qi, Jie / Hoyos, Diego Ibarra / Poon, S. Joseph

2022

Abstract: The design of high-entropy alloys (HEA) with desired properties is challenging due to their large compositional space. While various machine learning (ML) models can predict specific HEA solid-solution phases (SS), predicting high-entropy intermetallic ... ...

Abstract	The design of high-entropy alloys (HEA) with desired properties is challenging due to their large compositional space. While various machine learning (ML) models can predict specific HEA solid-solution phases (SS), predicting high-entropy intermetallic phases (IM) is underdeveloped due to limited datasets and inadequate ML features. This paper introduces feature engineering-assisted ML models that achieve detailed phase classification and high accuracy. By combining phase-diagram-based and physics-based features, it is found that the ML models trained on the Random Forest (RF) and Support Vector Machine (SVM) regressors, are able to classify individual SS and common IM (Sigma, Laves, Heusler, and refractory B2 phases) with accuracies ranging from 80 - 94%. The machine-learned features also enable the interpretation of IM formation. Furthermore, the efficacies of the RF, SVM, and neural network (NN) models are critically evaluated. The phase classification accuracies are found to decrease upon utilizing the NN model to train the datasets. The accuracy of the model prediction is validated by synthesizing 86 new alloys. This approach provides a practical and robust framework for guiding HEA phase design, particularly for technologically significant IM phases.
Keywords	Condensed Matter - Materials Science
Publishing date	2022-08-03
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Publisher Correction: High Entropy Alloys Mined From Binary Phase Diagrams.

Qi, Jie / Cheung, Andrew M / Poon, S Joseph

Scientific reports

2020 Volume 10, Issue 1, Page(s) 1844

Abstract: An amendment to this paper has been published and can be accessed via a link at the top of the paper. ...

Abstract	An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Language	English
Publishing date	2020-01-30
Publishing country	England
Document type	Published Erratum
ZDB-ID	2615211-3
ISSN	2045-2322 ; 2045-2322
ISSN (online)	2045-2322
ISSN	2045-2322
DOI	10.1038/s41598-020-58758-1
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Article: Phase Change-Induced Magnetic Switching through Metal-Insulator Transition in VO

Ma, Chung T / Kittiwatanakul, Salinporn / Sittipongpittaya, Apiprach / Wang, Yuhan / Morshed, Md Golam / Ghosh, Avik W / Poon, S Joseph

Nanomaterials (Basel, Switzerland)

2023 Volume 13, Issue 21

Abstract: The ability to manipulate spins in magnetic materials is essential in designing spintronics devices. One method for magnetic switching is through strain. In VO2 on TiO2 thin films, while VO2 remains rutile across the metal-insulator transition, the in- ... ...

Abstract	The ability to manipulate spins in magnetic materials is essential in designing spintronics devices. One method for magnetic switching is through strain. In VO2 on TiO2 thin films, while VO2 remains rutile across the metal-insulator transition, the in-plane lattice area expands going from a low-temperature insulating phase to a high-temperature conducting phase. In a VO2/TbFeCo bilayer, the expansion of the VO2 lattice area exerts tension on the amorphous TbFeCo layer. Through the strain effect, magnetic properties, including the magnetic anisotropy and magnetization, of TbFeCo can be changed. In this work, the changes in magnetic properties of TbFeCo on VO2/TiO2(011) are demonstrated using anomalous Hall effect measurements. Across the metal-insulator transition, TbFeCo loses perpendicular magnetic anisotropy, and the magnetization in TbFeCo turns from out-of-plane to in-plane. Using atomistic simulations, we confirm these tunable magnetic properties originating from the metal-insulator transition of VO2. This study provides the groundwork for controlling magnetic properties through a phase transition.
Language	English
Publishing date	2023-10-27
Publishing country	Switzerland
Document type	Journal Article
ZDB-ID	2662255-5
ISSN	2079-4991
ISSN	2079-4991
DOI	10.3390/nano13212848
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Article ; Online: High Entropy Alloys Mined From Binary Phase Diagrams.

Qi, Jie / Cheung, Andrew M / Poon, S Joseph

Scientific reports

2019 Volume 9, Issue 1, Page(s) 15501

Abstract: High entropy alloys (HEA) are a new type of high-performance structural material. Their vast degrees of compositional freedom provide for extensive opportunities to design alloys with tailored properties. However, compositional complexities present ... ...

Abstract	High entropy alloys (HEA) are a new type of high-performance structural material. Their vast degrees of compositional freedom provide for extensive opportunities to design alloys with tailored properties. However, compositional complexities present challenges for alloy design. Current approaches have shown limited reliability in accounting for the compositional regions of single solid solution and composite phases. For the first time, a phenomenological method analysing binary phase diagrams to predict HEA phases is presented. The hypothesis is that the HEA structural stability is encoded within the phase diagrams. Accordingly, we introduce several phase-diagram inspired parameters and employ machine learning (ML) to classify 600+ reported HEAs based on these parameters. Compared to other large database statistical prediction models, this model gives more detailed and accurate phase predictions. Both the overall HEA prediction and specifically single-phase HEA prediction rate are above 80%. To validate our method, we demonstrated its capability in predicting HEA solid solution phases with or without intermetallics in 42 randomly selected complex compositions, with a success rate of 81%. The presented search approach with high predictive capability can be exploited to interact with and complement other computation-intense methods such as CALPHAD in providing an accelerated and precise HEA design.
Language	English
Publishing date	2019-10-29
Publishing country	England
Document type	Journal Article
ZDB-ID	2615211-3
ISSN	2045-2322 ; 2045-2322
ISSN (online)	2045-2322
ISSN	2045-2322
DOI	10.1038/s41598-019-50015-4
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Book ; Online: Multi-Principal-Element Approach to High-Performance Thermoelectric Materials

Poon, S. Joseph / He, Jian

2019

Abstract: High-entropy alloys are characterized by high configurational entropy. Since the discovery of high-entropy alloys (HEA) in 2004, entropy engineering has provided a promising direction for exploiting composition, lattice disorder, band structure, and ... ...

Abstract	High-entropy alloys are characterized by high configurational entropy. Since the discovery of high-entropy alloys (HEA) in 2004, entropy engineering has provided a promising direction for exploiting composition, lattice disorder, band structure, and microstructure effects to advance thermoelectric performance. This review discusses the impact of entropy on thermoelectric properties and looks back at the role of multi-principal-element alloys, a weaker version of HEA, on the development of compositionally complex thermoelectric alloys in achieving high thermoelectric performance. The experimental and theoretical efforts in a wide range of material systems such as TAGS, LAST, half-Heusler, liquid-like copper chalcogenides, SnTe, and CuInTe2 chalcopyrites provide insights into the entropy engineering approach and also promise an emerging paradigm of high-entropy thermoelectrics. Comment: To be published in Encyclopedia of Materials Science, special issue on High Entropy Alloys
Keywords	Condensed Matter - Materials Science ; Condensed Matter - Disordered Systems and Neural Networks
Subject code	669
Publishing date	2019-11-09
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Interfacial Mixing Effect in a Promising Skyrmionic Material

Ma, Chung T. / Zhou, Wei / Kirby, Brian J. / Poon, S. Joseph

Ferrimagnetic Mn$_4$N

2022

Abstract: Interfacial mixing of elements is a well-known phenomenon found in thin film deposition. For thin-film magnetic heterostructures, interfacial compositional inhomogeneities can have drastic effects on the resulting functionalities. As such, care must be ... ...

Abstract	Interfacial mixing of elements is a well-known phenomenon found in thin film deposition. For thin-film magnetic heterostructures, interfacial compositional inhomogeneities can have drastic effects on the resulting functionalities. As such, care must be taken to characterize the compositional and magnetic properties of thin films intended for device use. Recently, ferrimagnetic Mn$_4$N thin films have drawn considerable interest due to exhibiting perpendicular magnetic anisotropy, high domain-wall mobility, and good thermal stability. In this study, we employed X-ray photoelectron spectroscopy (XPS) and polarized neutron reflectometry (PNR) measurements to investigate the interfaces of an epitaxially-grown MgO/Mn$_4$N/Pt trilayer deposited at 450 $^{\circ}$C. XPS revealed the thickness of elemental mixing regions of near 5 nm at both interfaces. Using PNR, we found that these interfaces exhibit essentially zero net magnetization at room temperature. Despite the high-temperature deposition at 450 $^{\circ}$C, the thickness of mixing regions is comparable to those observed in magnetic films deposited at room temperature. Micromagnetic simulations show that this interfacial mixing should not deter the robust formation of small skyrmions, consistent with a recent experiment. The results obtained are encouraging in terms of the potential of integrating thermally stable Mn$_4$N into future spintronic devices.
Keywords	Condensed Matter - Materials Science
Subject code	530
Publishing date	2022-08-04
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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