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At least 1,729 records · Page 96
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Effect of the Milling Conditions on the Properties of ZnO Doped with Fe

(Zn{sub 0.9}Fe{sub 0.1})O powders were produced with different ball to powder weight ratios (BPR) by ball milling of ZnO and Fe elemental powders. The BPR used were 15:1, 20:1, 25:1, and 30:1. The prepared samples were studied by x-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Mössbauer spectroscopy (MS). The XRD patterns showed a zinc oxide (ZnO) single phase with wurtzite structure, except for the 15:1 ratio, which exhibits an additionally bcc structure associated to α-Fe. The mean crystallite sizes were found to be around 100 Å. The Mössbauer spectra were fitted using two doublets, associated to the incorporation of Fe ions into the ZnO lattice, which correspond to the Fe{sup 3+} and Fe{sup 2+} oxidation states except for the 15:1 ratio, for which an additional sextet was necessary to obtain a good fit, this sextet was associated to segregated Fe into the sample. The increase of the BPR allowed that all Fe penetrated into the ZnO matrix. The magnetization measurement using VSM reveals that the system exhibits ferromagnetic behavior at room temperature. For sample with BPR 15:1, the ferromagnetism is due to the segregated Fe, and for higher BPRs, from 20:1 up to 30:1, we propose that their ferromagnetism is due to the percolation of polarons. These polarons appear due to the oxygen vacancies (detected by XRD) which are occupied by electrons, which appear in the charge balance. Exchange interaction between the electron spins located in the vacancies or holes and those of the magnetic impurities (Fe atoms) leads to the formation of bound magnetic polarons, which percolate, producing in this way magnetic behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Benchmark Analysis on Magnetic and Photoluminescence Properties of Selective Metal Ions Doped ZnS Nanoparticles

The creation of diluted magnetic semiconductors (DMSs) at lower dimensions that exhibit room temperature ferromagnetism (RTFM) has been given immense significance for the fabrication of a new class of spintronic devices through utilizing spin degrees of freedom besides charge nature of electrons. In this view, nanocrystals of ZnS doped with 4% concentration of Fe, Co, Ni, Cr, Mn, Sr, Cu, and Ce have been synthesized at room temperature (RT) by chemical co-precipitation method. The samples were examined by various characterization techniques like energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and photoluminescence (PL). EDS spectra revealed the existence of parent elements in the prepared samples. XRD characterization disclosed hexagonal structures of nanocrystals, and no secondary phases were observed in all the samples except for Cu and Ni doped ZnS. FTIR data confirmed the proper substitution of dopants in the host lattice as all the graphs have almost same stretchings. The magnetic nature of each sample was evaluated from M-H graphs of VSM, and it corroborated the transition of magnetic properties due to doping. Pristine ZnS showed diamagnetic nature, while Fe and Sr doped ZnS evinced strong ferromagnetic and anti-ferromagnetic properties, respectively. Photoluminescence studies on Ce, Sr and Mn doped ZnS samples revealed strong emission peaks with enhanced luminescence properties compared to bare ZnS. Cu, Cr and Mn doped ZnS exhibited a red shift in emission wavelengths, whereas Co doped ZnS showed emission peak shifted towards the blue region as compared to the host lattice.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Fabrication and Magnetic Characterization of CFO/NiO and CFO/NiS Heterostructures

Magnetic analysis of different magnetic bilayers and multilayers is an important step for designing next-generation multiferroic heterostructures. In this study, we have investigated the magnetic interaction at the interface in CFO/NiO hetero-structures grown by pulsed laser deposition on sapphire substrates. The thin film heterostructure samples were characterized by means of X-ray diffraction, scanning electron microscopy (SEM), energy disruptive X-ray spectroscopy (EDS), and superconducting quantum interference device (SQUID) for magnetic measurements. The XRD analysis on different samples shows the crystalline growth of the thin films. The SEM-EDS analysis provides information about structural and elemental compositions of the heterostructure films. A SQUID magnetometer was used to investigate the temperature and field-dependent magnetic properties. To better understand the magnetic properties of the thin film heterostructure samples, zero field cool (ZFC) and field cool (FC) magnetization data were analyzed. At low temperature, ferromagnetic hysteresis loop was observed. A shift in the M-H hysteresis curve was observed for the FC data from the ZFC data, which indicates the presence of exchange bias effect. In addition, we have examined the effect of antiferromagnetic NiS thin films on ferromagnetism of CFO. This study on the magnetic interaction between a ferromagnetic layer and an antiferromagnetic layer can advance the frontier for applications in spin valves, magnetic sensors, and magnetic random access memory.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Zero point fluctuations for magnetic spirals and Skyrmions, and the fate of the Casimir energy in the continuum limit

We study the role of zero-point quantum fluctuations in a range of magnetic states which on the classical level are close to spin-aligned ferromagnets. These include Skyrmion textures characterized by non-zero topological charge, and topologically-trivial spirals arising from the competition of the Heisenberg and Dzyaloshin-skii–Moriya interactions. For the former, we extend our previous results on quantum exactness of classical Bogomolny–Prasad–Sommerfield (BPS) ground-state degeneracies to the general case of Kähler manifolds, with a specific example of Grassmann manifolds Gr(M,N). These are relevant to quantum Hall ferromagnets with N internal states and integer filling factor M. A promising candidate for their experimental implementation is monolayer graphene with N = 4 corresponding to spin and valley degrees of freedom at the charge neutrality point with M = 2 filled Landau levels. We find that the vanishing of the zero-point fluctuations in taking the continuum limit occurs differently in the case of BPS states compared to the case of more general smooth textures, with the latter exhibiting more pronounced lattice effects. This motivates us to consider the vanishing of zero-point fluctuations in such near-ferromagnets more generally. We present a family of lattice spin models for which the vanishing of zero-point fluctuations is evident, and show that some spirals can be thought of as having nonzero but weak zero-point fluctuations on account of their closeness to this family. Between them, these instances provide concrete illustrations of how the Casimir energy, dependent on the full UV-structure of the theory, evolves as the continuum limit is taken.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Low temperature synthesis, photoluminescence, magnetic properties of the transition metal doped wurtzite ZnS nanowires

In this paper, we synthesized the transition metal ions (Mn, Cu, Fe) doped and co-doped ZnS nanowires (NWs) by a one-step hydrothermal method. The results showed that the solid solubility of the Fe{sup 2+} ions in the ZnS NWs was about two times larger than that of the Mn{sup 2+} or Cu{sup 2+} ions in the ZnS NWs. There was no phase transformation from hexagonal to cubic even in a large quantity transition metal ions introduced for all the samples. The Mn{sup 2+}/Cu{sup 2+}/Fe{sup 2+} related emission peaks can be observed in the Mn{sup 2+},Cu{sup 2+} and Fe{sup 2+} doped ZnS NWs. The ferromagnetic properties of the co-doped samples were investigated at room temperature. - graphical abstract: The stable wurtzite ZnS:TM{sup 2+} (TM=Mn, Cu, Fe) nanowires with room temperature ferromagnetism properties were obtained. The different elongation of unit cell caused by the different doped ions was observed. Highlights: ► The transition metal ions doped wurtzite ZnS nanowires were synthesized at 180 °C. ► There was no phase transformation from hexagonal to cubic even in a large quantity introduced for all the samples. ► The room temperature ferromagnetism properties of the co-doped nanowires were investigated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Toward a better understanding of the magnetocaloric effect: An experimental and theoretical study of MnFe{sub 4}Si{sub 3}

The intermetallic compound MnFe{sub 4}Si{sub 3} has been studied by high-resolution Time of Flight (TOF) neutron powder diffraction. MnFe{sub 4}Si{sub 3} crystallizes in the hexagonal space group P6{sub 3}/mcm with lattice constants of a=b=6.8043(4) Å and c=4.7254(2) Å at 310 K. Magnetic susceptibility measurements show clearly the magnetic transition from paramagnetism to ferromagnetism at about 302(2) K. Magnetic structure refinements based on neutron powder diffraction data with and without external magnetic field reveal strong evidence on the origin of the large magnetocaloric effect (MCE) in this material as a partial reordering of the spins between ∼270 K and 300 K. In addition, electronic structure calculations using the self-consistent, spin-polarized Tight Binding-Linear MuffinTin Orbital (TB-LMTO) method were also accomplished to address the “coloring problem” (Mn/Fe site preference) as well as the unique ferromagnetic behavior of this intermetallic compound. - Graphical abstract: Theoretical and experimental reinvestigation of the magnetic structure of MnFe{sub 4}Si{sub 3} for a better understanding of its large magnetocaloric effect (MCE). - Highlights: • Strong magnetic transition from paramagnetism to ferromagnetism at about 302(2) K. • MCE associated to a partial reordering of the spins between ∼270 K and 300 K. • DFT calculations show strong relation between MCE and spintronic materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

One-dimensional Co(II)/Ni(II) complexes of 2-hydroxyisophthalate: Structures and magnetic properties

The solvothermal reactions of 2-hydroxyisophthalic acid (H{sub 3}ipO) with M(NO{sub 3}){sub 2}∙6H{sub 2}O (M=Co, Ni) afforded two complexes [Co{sub 2}(HipO){sub 2}(Py){sub 2}(H{sub 2}O){sub 2}] (1) and [Ni(HipO)(Py)H{sub 2}O] (2) (Py=pyridine). They exhibit similar zig-zag chain structures with the adjacent two metal centers connected by a anti-syn bridging carboxylate group from the HipO{sup 2−} ligand. The magnetic measurements reveal the dominant antiferromagnetic interactions and spin-canting in 1 while ferromagnetic interactions in 2. Both of them exhibit magnetocaloric effect (MCE) with the resulting entropy changes (−ΔS{sub m}) of 12.51 J kg{sup −1} K{sup −1} when ΔH=50 kOe at 3 K for 1 and 11.01 J kg{sup −1} K{sup −1} when ΔH=50 kOe at 3 K for 2, representing the rare examples of one-dimensional complexes with MCE. - Graphical abstract: Synopsis: Two Co(II)/Ni(II) complexes with zig-zag chain structures have been reported. 1-Co shows cant-antiferromagnetism while 2-Ni shows ferromagnetism. Magnetocaloric effect is also found in both of them. - Highlights: • Two one-dimensional Co(II)/Ni(II) complexes were solvothermally synthesized. • The Co-complex exhibits canted antiferromagnetism. • The Ni-complex exhibits ferromagnetism. • Both of the complexes display magnetocaloric effect.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Two new Co(II)-MOFs based on polymeric chain building units: Crystal structures, and magnetic properties

Two new Co(II) metal-organic frameworks, namely [Co{sub 2}(bpm)(H{sub 2}O){sub 3}(L)]{sub n} (1) and ([Co(bpe)(H{sub 2}O)(H{sub 2}L)]·(bpe){sub 0.5}·(H{sub 2}O)){sub n} (2), (H{sub 4}L=1,1′:2′,1″-terphenyl-3,3″,4′,5′-tetracarboxylic acid, bpm=bis(4-pyridyl)amine, bpe=1,2-bis(4-pyridyl)ethene), have been obtained under hydrothermal conditions. Both complexes 1 and 2 have been characterized by elemental analysis, IR spectra, single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). Complexes 1 and 2 consist of 1D Co(II) chains bridging by carboxylate groups in syn-anti fashion. 1 shows a novel 3D tri-nodal (4,6,10)-connected net with a (3.4{sup 3}.5{sup 2}){sub 2}(3{sup 2}.4{sup 14}.5{sup 12}.6{sup 12}.7{sup 4}.8)(3{sup 2}.4{sup 2}.5{sup 5}.6{sup 4}.7{sup 2}) topology. While 2 exhibits a 2D sql layer. Magnetic susceptibility measurements indicate that both 1 and 2 show weak antiferromagnetic interactions between the adjacent Co(II) ions in 300–8 K for 1 and 300–16 K for 2, respectively, and then 2 also displays ferromagnetic coupling at lower temperatures. - Graphical abstract: Two Co(II) coordination polymers with similar metal chain bridging by carboxylates in syn-anti fashion have been synthesized. Both 1 and 2 show weak antiferromagnetic interactions in high temperature, and then 2 also displays ferromagnetic coupling at lower temperatures. - Highlights: • Two Co(II) coordination polymers with similar metal chain bridging by carboxylates. • A novel 3D (4,6,10)-connected net and a 2D sql layers. • A antiferromagnetic coupling at high temperature for 1 and 2. • A ferromagnetic coupling at lower temperature for 2.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Hydrothermal synthesis and magnetic properties of CuO hollow microspheres

Graphical abstract: - Highlights: • CuO hollow microspheres were synthesized through hydrothermal route. • The possible growth mechanism was proposed according to the experimental results. • CuO hollow microspheres show an anomalous ferromagnetic behavior at 5 K and 300 K. - Abstract: In the present work, CuO hollow microspheres with the diameter about 2 μm were successfully synthesized through a facile hydrothermal method. The phase purity, morphologies and structure features of the as obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy, respectively. It was found that reaction temperature, reaction time and different volume ratios of ethanol and distilled water played important roles on the morphologies of the obtained CuO hollow microspheres. The possible formation mechanism was also proposed according to the corresponding experimental results. The magnetic properties were investigated by superconducting quantum interference device, revealing that the CuO hollow microspheres exhibited an anomalous ferromagnetic behavior at 5 K and 300 K. At the same time, the origin of the ferromagnetism in CuO hollow microspheres was also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Structural, electrical and magnetic properties of (Bi{sub 0.9}RE{sub 0.1})(Fe{sub 0.97}Co{sub 0.03})O{sub 3} (RE = Nd and Gd) thin films

Highlights: • Nd–Co and Gd–Co codoped BiFeO{sub 3} thin films are synthesized by chemical solution deposition method. • Enhanced magnetic property is observed in BGFC thin film at room temperature. • The onset electric field of FN tunneling of the films is associated with band gaps. • Both ferromagnetism and diamagnetism coexist in the BNFC film. - Abstract: Rhombohedral (Bi{sub 0.9}RE{sub 0.1})(Fe{sub 0.97}Co{sub 0.03})O{sub 3} (RE = Nd and Gd) thin films were deposited on FTO substrates by using a chemical solution deposition method. Raman scattering spectra reveal that the BiFeO{sub 3} lattices are able to incorporate Nd/Gd and Co ions with no effect on the basic rhombohedral structure. The chemical shift of Bi 4f, Fe 2p and O 1s core levels of the films is investigated by the X-ray photoelectron spectroscopy (XPS) analysis. The presence of defects in the films has been estimated through XPS study, which has a great effect on the dielectric dispersion and ferroelectric polarization. The intrinsic density of free electrons associated with band gap is the dominating factor which controls the FN tunneling conductance mechanism of the films. Both ferromagnetism and diamagnetism coexist in the BNFC film, while only ferromagnetism is observed in the BGFC film.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Structural, magnetic and optical properties of a dilute magnetic semiconductor based on Ce{sub 1−x}Co{sub x}O{sub 2} thin film grown on LaAlO{sub 3}

Highlights: • Co doped CeO{sub 2} was grown on LaAlO{sub 3} (0 0 1) via a modified sol–gel spin-coating technique. • The concentration of the Co ions was varied from 1 to 15 at.%. • The incorporation of 5 at.% of Mn ions was found to provide formation of exceptionally magnetic moment. • This amount demonstrated a giant magnetic moment of 1.09 μ{sub B}/Co. • This amount reduced the optical band gap and enhanced the optical performance. - Abstract: The enhancement of the room temperature ferromagnetism and optical properties of the dilute magnetic metal oxides is a crucial clue to construct spin-based optoelectronic devices. In this work, Ce{sub 1−x}Co{sub x}O{sub 2} (0.01 ≤ x ≤0.15) thin films were prepared via ethylene glycol modified sol–gel spin coating technique on the LaAlO{sub 3} (0 0 1) substrate to enhance their room temperature ferromagnetism and optical properties. The structures, magnetic and optical properties of the prepared films were characterized by X-ray diffraction, atomic force microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, SQUID magnetometer, X-ray photoelectron spectroscopy and UV–vis spectrophotometer. The results demonstrated that a single phase cubic structure was formed, implying the substitution of Co ions into the Ce ions sites. The prepared films showed room temperature ferromagnetism with saturation magnetic moment of 1.09 μ{sub B}/Co was achieved for 5 at.% Co-doped CeO{sub 2}. This film exhibited high optical transparency of 85% and low optical band energy gap of 3.39 eV. The improved magnetic and optical properties are argued to the increase of the density of the oxygen vacancies into the cerium oxide crystal structure due to the incorporation of Co ions.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Comprehensive studies of structural, electronic and magnetic properties of Zn{sub 0.95}Co{sub 0.05}O nanopowders

Highlights: • Zn{sub 0.95}Co{sub 0.05}O nanopowders are characterized by high structural order. • Co atoms show no tendency for Co–Co clustering and Co–Ov complexes formation. • Co–O–Co clustering along the c-axis has not lead to ferromagnetic order. • XMCD provides no evidence of magnetic polarization of O 2p and Co 3d states. - Abstract: X-ray absorption (XANES, EXAFS, XMCD) and photoelectron (XPS) spectroscopic techniques were employed to study local structural, electronic and magnetic properties of Zn{sub 0.95}Co{sub 0.05}O nanopowders. The substitutional Co{sup 2+} ions are incorporated in ZnO lattice at regular Zn sites and the sample is characterized by high structural order. There was no sign of ferromagnetic ordering of Co magnetic moments and the sample is in paramagnetic state at all temperatures down to 5 K. The possible connection of the structural defects with the absence of ferromagnetism is discussed on the basis of theoretical calculations of the O K-edge absorption spectra.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Role of nickel doping on structural, optical, magnetic properties and antibacterial activity of ZnO nanoparticles

Highlights: • The XRD analyses revealed that the synthesizes nickel doped ZnO (Zn{sub 1−x}Ni{sub x}O, x = 0.0, 0.03, 0.06 and 0.09) nanostructures have hexagonal wurtzite structure. • The photoluminescence measurements revealed that the broad emission was composed of different bands due to zinc and oxygen vacancies. • X-ray photoelectron spectroscopy (XPS) confirmed the Ni incorporation in ZnO lattice as Ni{sup 2+} ions. • Room temperature ferromagnetism was observed due to the oxygen vacancies and zinc interstitials are the main reasons for ferromagnetism in Ni doped ZnO NPs. - Abstract: Zn{sub 1−x}Ni{sub x}O nanoparticles were synthesized by co-precipitation method. The crystallite sizes of the synthesized samples found to decrease from 38 to 26 nm with increase in nickel concentration. FTIR spectra confirmed the presence of Zn−O stretching bands at 577, 573, 569 and 565 cm{sup −1} in the respective ZnO NPs. Optical absorption spectra revealed the red shifted and estimated band gap is found to decrease with increase of Ni doping concentration. The PL spectra of all the samples exhibited a broad emission at 390 nm in the visible range. The carriers (donors) bounded on the Ni sites were observed from the micro Raman spectroscopic studies. Pure and Ni doped ZnO NPs showed significant changes in the M–H loop, especially the diamagnetic behavior changed into ferromagnetic nature for Ni doped samples. The antiferromagnetic super-exchange interactions between Ni{sup 2+} ions is increased in higher Ni doped ZnO NPs and also their antibacterial activity has been studied.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Dense nanocrystalline yttrium iron garnet films formed at room temperature by aerosol deposition

Highlights: • We deposit yttrium iron garnet films at room temperature using aerosol deposition. • Films are 96% of theoretical density for yttrium iron garnet. • We report magnetic and structural properties post-deposition and post-annealing. • Low-temperature annealing decreases the FMR linewidth. • We discuss features of the FMR spectra at each anneal temperature. - Abstract: We have employed aerosol deposition to form polycrystalline yttrium iron garnet (YIG) films on sapphire at room temperature that are 90–96% dense. We characterize the structural and dynamic magnetic properties of the dense films using scanning electron microscopy, X-ray diffraction, and ferromagnetic resonance techniques. We find that the as-deposited films are pure single-phase YIG formed of compact polycrystallites ∼20 nm in size. The ferromagnetic resonance mode occurs at 2829 G with a linewidth of 308 G. We perform a series of successive anneals up to 1000 °C on a film to explore heat treatment on the ferromagnetic resonance linewidth. We find the narrowest linewidth of 98 G occurs after a 750 °C anneal.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Room temperature magnetic ordering and analysis by bound magnetic polaron model of Yb3+ doped nanocrystalline zinc oxide (Zn0.98Yb0.02O)

Highlights: • ZnO and Yb doped ZnO are synthesized by co-precipitation method. • Rietvelt anlysis of XRD patterns confirms the complete substitution of Yb{sup 3+} in ZnO. • Vacancy and defect mediated RTFM is introduced in doped ZnO. • BMP model successfully analyze the magnetic property of Zn{sub 0.98}Yb{sub 0.02}O. - Abstract: Nanocrystalline ZnO and Yb-doped ZnO (Zn{sub 0.98}Yb{sub 0.02}O) are prepared by simple co-precipitation method. The pure crystallographic phases of ZnO and Zn{sub 0.98}Yb{sub 0.02}O are confirmed by Rietveld analyses of XRD patterns. Raman and photoluminescence spectra recorded at room temperature (RT) indicates that lattice defects and oxygen vacancy in Zn{sub 0.98}Yb{sub 0.02}O is more than that of ZnO. Magnetic measurements of ZnO and Zn{sub 0.98}Yb{sub 0.02}O are carried out from 300 to 5 K. Ferromagnetic ordering is observed in Zn{sub 0.98}Yb{sub 0.02}O at RT and the strength of the ordering increases with the lowering of temperature. Ferromagnetism of Zn{sub 0.98}Yb{sub 0.02}O is attributed to the oxygen vacancy introduced by annealing in vacuum. Magnetization vs. temperature curve is well fitted by the combination of 3D spin wave and Curie-Weiss law, which suggest simultaneous presence of para- and ferro-magnetic phases in Zn{sub 0.98}Yb{sub 0.02}O. Ferromagnetic ordering is successfully explained by vacancy mediated bound-magnetic polaron model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic force microscopy revealing long range molecule impact on magnetic tunnel junction based molecular spintronics devices

Magnetic force microscopy (MFM) vividly showed that organometallic molecules, when bridged between two ferromagnetic electrodes along the cross-shaped magnetic tunnel junction edges transformed the magnetic electrodes itself. Molecules impacted a large area of ferromagnetic leads around the junction at room temperature and complement the previous magnetic measurements showing molecule effect on pillar form magnetic tunnel junctions. This molecule induced changes in the magnetic electrodes impacted the transport of the magnetic tunnel junction and stabilized as much as seven orders smaller current at room temperature. We have discussed the current suppression phenomenon in the recent publication [Ref. Tyagi et al. Organic Electronics, 2019, Vol. 64, p 188]; however, we did not provide any direct evidence of molecule impact on ferromagnetic electrodes around molecule junction. Our MFM studies in this paper suggests that molecule effect was observable several μm away from the molecule-metal junctions. Furthermore, our study suggests that magnetic tunnel junction based molecular spintronics devices can be a gateway to a vast range of commercially viable and robust futuristic computer devices and highly correlated materials.

42 ENGINEERING↗
DOE OSTI2025

Universal Magnetic Phases in Twisted Bilayer MoTe 2

Twisted bilayer MoTe 2 (tMoTe 2 ) has emerged as a robust platform for exploring correlated topological phases, yet the evolution of its magnetism and topology with twist angle remains an open question. Here, we systematically map the magnetic phase diagram of tMoTe 2 by using local optical spectroscopy and scanning nanoSQUID-on-tip magnetometry. We identify spontaneous ferromagnetism at filling factors ν = −1 and −3 across twist angles from 2.1° to 3.7°, revealing a universal, twist-angle-insensitive ferromagnetic phase. At 2.1°, we further observe robust ferromagnetism at ν = −5, absent at larger twist angles. Temperature-dependent measurements reveal a contrasting twist-angle dependence of the Curie temperatures between ν = −1 and −3, indicating a distinct interplay between the exchange interactions and bandwidth for the two Chern bands. Despite broken time-reversal symmetry, no topological gap is detected at ν = −3. Furthermore, our results establish a global framework for understanding and controlling magnetic order in tMoTe 2 .

Insulators↗
DOE OSTI2013

Structural, optical and magnetic properties of ZnOFe/ZnO multilayers

ZnOFe/ZnO multilayers (MLs) with the constant composition and the different thickness in ZnOFe layers have been prepared by helicon plasma sputtering. The XRD patterns of ZnOFe/ZnO MLs before annealing showed only ZnO diffraction peaks while one after annealing indicated the phases of ZnO and ZnFe{sub 2}O{sub 4}. The magnetization curves of ZnOFe/ZnO MLs before and after annealing showed ferromagnetic behavior. The origin of ferromagnetism in ZnOFe/ZnO MLs before annealing is considered to be due to the formation of defects/vacancies resulting from the substitution of Fe{sup 3+} ions for Zn{sub 2+} ions in ZnOFe layers irrespective of the mixed Fe valence states seen in XANES spectra. The ferromagnetic behavior after annealing is due to the formation of ZnFe{sub 2}O{sub 4}, which was confirmed by XRD, XPS, RBS measurements.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗