Room temperature ferromagnetism in un-doped amorphous HfO_2 nano-helix arrays

Amorphous HfO2 nano-helix arrays with different screw pitches were fabricated by the glancing angle deposition technique. Room temperature ferromagnetism was achieved in this undoped amorphous HfO2 nanostructure, which is attributed to singly charged oxygen vacancies. The different magnetic behavior and photoluminescence in flat film and nano-helix arrays originate from the distinction of defect components. This study could facilitate the understanding of ferromagnetism origin in undoped HfO2, it also suggests a possible way to alter the intrinsic defects in amorphous HfO2.

Room Temperature Ferromagnetism in Ga1-xHoxN （x=0.0 and 0.05） Diluted Magnetic Semiconductor Thin Films

Holmium doped GaN diluted magnetic semiconductor thin films have been prepared by thermal evaporation technique and subsequent ammonia annealing. X-ray diffraction mea- surements reveal all peaks belong to the purely hexagonal wurtzite structure. Surface mor- phology and composition analysis were carried out by scanning electron microscopy and energy dispersive spectroscopy respectively. The room temperature ferromagnetic proper- ties of Gal-xHoxN （x=0.0, 0.05） films were analyzed using vibrating sample magnetometer at room temperature. Magnetic measurements showed that the undoped films （i.e. GaN） exhibited diamagnetic behavior, while the Ho-doped （Gao.95Hoo.05N） film exhibited a ferro- magnetic behavior.

Room temperature ferromagnetism in ultra-thin van der Waals crystals of 1T-CrTe2

Although many emerging new phenomena have been unraveled in two dimensional(2D)materials with long-range spin orderings,the usually low critical temperature in van der Waals(vdW)magnetic material has thus far hindered the related practical applications.Here,we show that ferromagnetism can hold above 300 K in a metallic phase of 1T-CrTe2 down to the ultra-thin limit.It thus makes CrTe2 so far the only known exfoliated ultra-thin vdW magnets with intrinsic long-range magnetic ordering above room temperature.An in-plane room-temperature negative anisotropic magnetoresistance(AMR)was obtained in ultra-thin CrTe2 devices,with a sign change in the AMR at lower temperature,with−0.6%and+5%at 300 and 10 K,respectively.Our findings provide insights into magnetism in ultra-thin CrTe2,expanding the vdW crystals toolbox for future room-temperature spintronic applications.

Room Temperature Magnetic Behavior of Sol-Gel Synthesized Mn Doped ZnO

Mn doped ZnO nano-crystallites were synthesized by state of the art sol-gel derived auto- combustion technique. As-burnt powder was investigated with different characterization techniques to explore the properties of Mn doped ZnO dilute magnetic semiconductor. X- ray diffraction measurements indicate that Mn doped ZnO retain wurtzite type hexagonal crystal structure like ZnO. Compositional and morphological studies were carried out by energy dispersive X-ray analysis and scanning electron microscopy, respectively. Temperature dependent resistivity of the sample exhibited the semiconducting behavior of the DMS material. Room temperature magnetic properties determined by vibrating sample magnetometer, revealed the presence of ferromagnetic and diamagnetic contributions in Mn doped ZnO.

Ferromagnetism of Zn_(1-x)Cu_xO Polycrystalline Made by Solid State Reaction

The Zn1-xCuxO polycrystalline materials were prepared by doping CuO into wurtzite ZnO through solid state reaction. The high concentration of copper doping in ZnO exhibited remarkable room temperature ferromagnetism. The Experiments showed that the magnetization saturation rose with the increase of Cu content. For the low Cu content sample, the hysteresis loop was slightly tilted which indicated that the diamagnetism coexisted in this sample. The temperature dependence of magnetization of Zn1-xCuxO revealed that the magnetic exchange coupling depended on the doping concentration of Cu and there were many different local environments for magnetism. The measured hysteresis loop and temperature dependence of magnetization were overall performance of the magnetism coming from a wide distribution of ferromagnetic exchange couplings.

Room temperature ferromagnetic property of Fe-Y(Fe:Y-6.5) composite oxide nano-cluster via an extremely easy and scalable method

A novel Fe-Y composite oxide(Fe:Y-6.5) nanocluster was synthesized by self-assembly approach.The α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline with diameter around 10 nm are homogeneously assembled to form a cluster architecture which are constituted of Fe6.5Y composite oxide particles.Additional oxygen vacancies are introduced with cubic-Y_(2)O_(3),and the oxygen vacancies as Fe^(3+)-V_(0)-Y^(3+) between α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline are generated by self-assembly process.Magnetic hysteresis loops recorded by vibrating sample magnetometry at 273 K display a ferromagnetic order,related to the fact that Fe^(3+)-V_(o)-Y^(3+) act as defect centers in the bound magnetic polaron model for Fe-Y composite oxide nanomaterial.The ferromagnetic prope rties are proportional to oxygen vacancy co ntents,and maximum magnetization(M_(m)) value of the nano-cluster reaches 5.14 A·m^(2)/g.

High Curie temperature and perfect spin filtering effect in a single layer Ga_(2)O_(3)magnetic tunnel junction

The electronic structure and magnetic properties of single layer Ga_(2)O_(3)in the presence of Ga and O vacancies are studied by first principles method based on density functional theory.The results show that the introduction of Ga vacancy(VGa)leads to a non-zero magnetic moment in singlelayer two-dimensional(2D)Ga_(2)O_(3),while VO does not.We find that Ga vacancies in two different symmetric positions can lead to spin polarized ground states.Notably,when the VGa ratio is greater than 1/16(indicating one Ga vacancy per 16 Ga atoms),single-layer 2D Ga_(2)O_(3)exhibits semi-metallic properties and its spin polarization reaches 100%at the Fermi level.Calculations of these two Ga vacancy systems also indicate a potential long-range ferromagnetic order at a high Curie temperature(355.8 K).Finally,a single layer 2D Ga_(2)O_(3)with high GaI vacancy(VGaI)ratio can be used as the ferromagnetic layer to obtain the magnetic tunnel junction(MTJ)with high spin filtering effect at the Fermi level.Ga vacant Ga_(2)O_(3)/MgO/Ga vacant Ga_(2)O_(3)MTJ exhibits excellent spin-filtering effect(with 100%spin polarization)and a giant tunneling magneto resistance(TMR)ratio(up to 1.12×10^(3)%).The results of this paper show that the MTJ based on two-dimensional Ga_(2)O_(3)with room temperature ferromagnetism exhibits reliable performance,showing the possibility of potential applications in spintronics.

Current spin polarization and spin injection efficiency in ZnO-based ferromagnetic semiconductor junctions

[FeNi（3 nm）/Zn1-xCoxO（3 nm）]2/ZnO（d nm）/[Zn1-xCoxO（3 nm）/Co（3 nm）]2 （d=3 and 10） semiconductor junctions were prepared by magnetron sputtering system and photolithography. The spin valve effect was observed in these junctions because the utility of the ferromagnetic composite layers acted as soft and hard magnetic layers. The electrical detection was performed by measuring the magnetoresistance of these junctions to investigate the current spin polarization asc in the ZnO layer and the spin injection efficiency η of spin-polarized electrons. asc was reduced from 11.7% （and 10.5%） at 90 K to 7.31% （and 5.93%） at room temperature for d=3 （and d=10）. And η was reduced from 39.5% （and 35.5%） at 90 K to 24.7% （and 20.0%） at room temperature for d=3 （and d=10）.

Dielectric and magnetic properties of(Zn, Co) co-doped SnO_2 nanoparticles

Polycrystalline samples of（Zn, Co） co-doped SnO2 nanoparticles were prepared using a co-precipitation method. The influence of（Zn, Co） co-doping on electrical, dielectric, and magnetic properties was studied. All of the（Zn, Co） co-doped SnO2 powder samples have the same tetragonal structure of SnO2. A decrease in the dielectric constant was observed with the increase of Co doping concentration. It was found that the dielectric constant and dielectric loss values decrease, while AC electrical conductivity increases with doping concentration and frequency. Magnetization measurements revealed that the Co doping SnO2 samples exhibits room temperature ferromagnetism. Our results illustrate that（Zn, Co） co-doped SnO2 nanoparticles have an excellent dielectric, magnetic properties, and high electrical conductivity than those reported previously, indicating that these（Zn, Co） co-doped SnO2 materials can be used in the field of the ultrahigh dielectric material, high frequency device, and spintronics.

Effect of samarium doping on structural, optical and magnetic properties of vertically aligned ZnO nanorod arrays

Samarium doped vertically aligned one dimensional ZnO nanorod（NR） arrays were grown by vapor phase transport（VPT） method through vapor solid（VS） growth process. Influence of different concentrations（0% to 8%） of Sm（all Sm contents in the paper are in mass fraction） on the ZnO NR arrays were investigated by X-ray diffraction（XRD）, field emission scanning electron microscopy（FESEM）, photoluminescence（PL）, Raman spectroscopy and vibrating sample magnetometry（VSM） techniques, respectively. X-ray diffraction studies revealed that the ZnO NR arrays were perfectly oriented along（002） crystallographic orientation with wurtzite crystal structure. Photoluminescence results showed an increase in oxygen vacancies due to increase in Sm doping. M-H curves revealed enhanced ferromagnetic behavior, and the magnetic moment values were 0.45, 0.363, 1.694, 3.613 and 2.197 emu/cm^3 for（0–8%） Sm doped ZnO NR arrays respectively. The curve revealed that paramagnetic behavior was observed for undoped ZnO NR arrays and on increasing the Sm dopant to 4%, paramagnetic switched to ferromagnetic behavior.

Structural and magnetic properties of Yb-implanted GaN

N-type, p-type and unintentionally-doped GaN were implanted with Yb ions by double energy ion im- plantation and the samples were annealed at 900 ℃. The structural and magnetic properties of the samples have been studied by high-resolution X-ray diffraction （HRXRD）, Raman scattering and with a superconducting quan- tum interference device （SQUID）. No second phase has been observed and implantation induced defects can not be completely removed by rapid thermal annealing. The annealed samples show magnetic anisotropy and clear ferromagnetic behavior at room temperature. P-, u- and n-GaN：Yb samples show an effective magnetic moment of 1.60, 1.24 and 0.59 μB/Yb, respectively.

Spray Pypolysed Thin Film Transparent Ferromagnetic Sdmiconductors for Spintronics

1 Results Inducing order in spin degree of freedomof charge carriers in conventional semiconductors and gettingroomtemperature ferromagnetism(RTFM) is an ongoing challenge in realizing spintronic devices .