Giant Magnetization Research Articles

Giant magnetization on Mn3Ga ultra-thin films grown by magnetron sputtering on SiO2/Si(001)

Mn3Ga films were grown by rf-sputtering on SiO2/Si(001) substrates at 300 °C. Ultra-thin films with 2 nm of thickness are composed of small grains with an in-plane diameter ∼27 nm. The film exhibits an out-of-plane saturation magnetization Ms⊥ = 1690 emu/cm3 (15 times the bulk magnetization value) and in-plane Ms// = 216 emu/cm3, corresponding to 3.3 and 0.43μB/Mn at. Giant magnetization is attributed to uncompensated Mn moments located at the intergrain boundaries. No surface anisotropy is expected due to the high anisotropy constant of Mn3Ga. Ms decreases as the film thickness increases due to grain growth and subsequent decrease in intergrain boundary surface area. Magnetic M(H) loops remain anhysteretic for thickness ≤10 nm, corresponding to an average grain size 10 nm exhibit coercivity between 9 and 19 kOe and Ms from 25 to 72 emu/cm3 with a residual weak ferromagnetic component. Hysteretic M(H) loops are the signat...

Giant magnetization canting due to symmetry breaking in zigzag Co chains on Ir(001)

We demonstrate a canted magnetization of biatomic zigzag Co chains grown on the (5 × 1) reconstructed Ir(001) surface using density functional theory (DFT) calculations and spin-polarized scanning tunneling microscopy (SP-STM) experiments. It is observed by STM that biatomic Co chains grow in three different structural configurations. Our DFT calculations show that they are all in a ferromagnetic (FM) state. Two chain types possess high symmetry due to two equivalent atomic strands and an easy magnetization direction that is along one of the principal crystallographic axes. The easy magnetization axis of the zigzag Co chains is canted away from the surface normal by an angle of 33°. This giant effect is caused by the broken chain symmetry on the substrate in combination with the strong spin–orbit coupling of Ir. SP-STM measurements confirm the stable FM order of the zigzag chains with a canted magnetization.

Giant magnetism in punched zigzag-edged triangular-shaped graphene nanodisks

We observe, for the first time, a very large magnetism in the nano-sized (7–27 A) punched graphene nanodisks (PGNDs) i.e., zigzag-edged triangular PGNDs (ZET-PGNDs). A first-principles method has been employed to investigate their electronic and magnetic properties. Similar to a regular or unpunched ZET-GND where the spin value scales with the linear dimension of the ZET-GND arising from the topological frustration of the π bonds and the induced spin distributions in graphene structures, the magnetic moment in a PGND increases with its size very rapidly depending on the type of punching. Two types of the punched nanodisks have been discussed. In one type of PGND, the magnetic moment of the punched out smaller GND is added to the magnetic moment of the host GND and the resultant net magnetism is, thus, equal to the sum of the magnetic moments of the host GND and that of the punched out smaller GND. In the other type of the PGND, the magnetic moment of the punched out smaller GND is subtracted from the magnetic moment of the host GND and the net value of the magnetic moment is the difference of the magnetic moments of the host GND and that of the punched out smaller GND. One may, thus, enhance the magnetism of a GND by making an appropriate choice of the punching. It may have large magnetic moments in the passivated ZET-PGNDs beyond the nanoscale at room temperature. These punched graphene fragments may be employed for the preparation of several kinds of the electronic and spintronic devices possessing exotic features.

Colossal increase in negative magnetization, exchange bias and coercivity in samarium chromite due to a strong coupling between Sm3+–Cr3+ spins sublattices

We report giant temperature dependent negative magnetization (magnetization reversal) along with a large exchange bias and large coercivity in SmCrO3. The static magnetization measurements show the negative magnetization below ~192 K, due to competition between the external field, thermal activation energy and antiparallel Sm3+–Cr3+ spin interaction. At further lower temperatures, Sm3+ spins show an increased alignment due to the internal induced field of Cr3+ spins with minimum magnetization ~ − 0.037 emu g−1. The temperature dependent exchange bias shows non-monotonic behavior. At 35 K, the exchange bias ceases to exist due to the orientation of Sm3+ moments with respect to canted Cr3+ moments. The crossover temperature decreases from ~191 K at 100 Oe to ~153 K at 250 Oe. The training effect further confirms the exchange bias in SmCrO3. The dynamic magnetization measurements exhibit anomalies around spin reorientation transition (TSR ~ 34 K) and Nèel transition (TN ~ 192 K) which is consistent with static measurement and no frequency dependence was observed. The room temperature Raman spectra of SmCrO3 show peaks at ~364, ~375 and ~456 cm−1 suggesting O-Cr-O bending modes within the octahedral.

Angular dependence of giant magneto impedance and magnetic characteristic of Co-based wire in different magnetic field ranges

Angular dependence of the giant magneto impedance (GMI), hysteresis loops and magnetization curves have been investigated in amorphous wires with respect to direction and amplitude of the magnetic field in room temperature. The measurements were performed at different orientation angles of the applied magnetic field relative to the wire axis and various magnetic field strengths in moderate (0–200 Oe) and high (0–5000 Oe) ranges. The highest GMI response (500%) and magnetization (100 emu/gr) were found for angles close to the wire axis in high magnetic field range. By increasing the angle from 0°, in moderate external magnetic fields the GMI and magnetization decrease without reaching the saturation. However, in high magnetic fields (~ 5000 Oe) these parameters are nearly constant and almost saturated for all angles. In both magnetic field ranges, increasing the angle of applied field widens the impedance curves.

Thickness Dependence of Fe3O4/MgO Thin Film Properties: Density Functional Theory Investigation

In this work, the thickness dependence of Fe3O4(111)/MgO thin films, were simulated using density-functional theory. From the results, even though the total DOS in bulk structure presents a half-metallic behavior, the DOS of all Fe3O4 (111) films demonstrates that they are metallic. The specific magnetization as a function of film thickness is found to satisfy the inverse power law. Indeed, the noncompensation of spin moments is also observed to be the main majority effect in the enhancement of giant magnetization. Moreover, the high spin polarization value is discovered in the compensation models and tends to reach −80% with increasing the thickness.

Facile synthesis of single-phase spherical α″-Fe16N2/Al2O3 core-shell nanoparticles via a gas-phase method

When nitrogen was inserted into the spherical α-Fe/Al2O3 core shell of 45 nm nanoparticles, the XRD pattern showed a clear change in the crystal modification from a body-centered cubic crystal to that of a single-phase α″-Fe16N2 structure. SEM, TEM, and energy-dispersive X-ray spectroscopy mapping analysis gave the particle size distributions, the shell thickness, and the Fe and Al elements. An examination of the total electron yield (surface sensitive) and fluorescence yield (bulk sensitive) of X-ray absorption fine structure on Fe and N atoms of these core shell nanoparticles confirmed the nitriding of the core iron and showed iron oxide formations on the core surface, indicating stability and resistivity performance. The nitriding process also changed the magnetic properties from paramagnetic to ferromagnetic with a coercivity above 3000 Oe, indicating a promising material for a “rear-earth-free” giant magnet.

Strong stray fields in systems of giant magnetic anisotropy magnets

This paper reviews research into a little-studied phenomenon in which strong stray fields arise in ferromagnets with giant magnetic anisotropy. Conditions for this to occur and for the fields to be stable are discussed. A classification of strong fields is presented. For different field types, limiting field strength values on approaching singular points are determined. Applications of the stray fields in various technical devices are considered.

Strain induced giant magnetism in epitaxial Fe16N2 thin film

We report a direct observation of giant saturation magnetization in Fe16N2. By exploiting thin film epitaxy, which provides controlled biaxial stress to create lattice distortion, we demonstrate that giant magnetism can be established in Fe16N2 thin film coherently grown on MgO (001) substrate. Explored by polarized neutron reflectometry, the depth-dependent saturation magnetic induction (Bs) of epitaxial Fe16N2 thin films is visualized, which reveals a strong correlation with the in-plane lattice parameter and tensile strain developed at near substrate interface. With controlled growth process and dimension adjustment, the Bs of these films can be modulated over a broad range, from ∼2.1 Tesla (T) (normal Bs) up to ∼3.1 T (giant Bs).

Preparation and electromagnetic properties of in-situ Ba 0.8 Sr 0.2 TiO 3 /YFeO 3 composites

Ba0.8Sr0.2TiO3/YFeO3 (BST/YIP) composites with giant dielectric constants and high saturation magnetizations were synthesized via the in-situ growth solid-state method. The BST/YIP composites were sintered at 1350 °C, using Ba0.8Sr0.2TiO3 and Y3Fe5O12 as raw materials. The phase composition and surface morphology of the composites were investigated using XRD and SEM, respectively. The dielectric and magnetic properties of the composites were also studied. The results show that the BST/YIP composites have giant dielectric constants and high saturation magnetization. For the 40% BST/60% YIP composite, the dielectric constant and saturation magnetization are about 100,000 and 6.6, respectively. The giant dielectric constants of the BST/YIP composites are mainly attributed to the Maxwell–Wagner polarization.

Сильные поля рассеяния в системах магнитов с гигантской магнитной анизотропией

Сильные поля рассеяния в системах магнитов с гигантской магнитной анизотропией

Ba0.6Sr0.4TiO3/CoFe2O4 Composite with Giant Dielectric Constant and High Saturation Magnetization

Ba0.6Sr0.4TiO3/CoFe2O4 (BST/CFO) composites were synthesized via the conventional solid-state reaction method. The phase composition and surface morphology of the composites were investigated using X-ray diffractometer (XRD) and scanning electron microscope (SEM), respectively. The dielectric and magnetic properties of the composites were studied. The results show that the BST/CFO composites have giant dielectric constants and very high remnant magnetisation. The dielectric behavior of the BST/CFO composites can be explained by the Maxwell–Wagner Model.

Correlator product state study of molecular magnetism in the giant Keplerate Mo72Fe30

We have studied the properties of the giant Keplerate molecular magnet ${\mathrm{Mo}}_{72}{\mathrm{Fe}}_{30}$, as a function of applied magnetic field, using the correlator product state (CPS) tensor network ansatz. The magnet is modeled with an $S=5/2$ antiferromagnetic Heisenberg Hamiltonian on the 30-site icosidodecahedron lattice, a model for which exact diagonalization is infeasible. The CPS ansatz produces significant improvements in variational energies relative to previous studies using the density matrix renormalization group, a result of its superior ability to handle strong correlation in two-dimensional spin systems. The CPS results reaffirm that the ground-state energies adhere qualitatively to the parabolic progression of the rotational band model (RBM), but show important deviations near 1/3 of the saturation field. These deviations predict anomalous behavior in the differential magnetization and heat capacity that can not be explained by the RBM alone. Finally, we show that these energetic deviations originate from a qualitative change in the ground state that resembles a finite-size analog of a phase transition.

Fabrication of $\hbox{Fe}_{16}\hbox{N}_{2}$ Films by Sputtering Process and Experimental Investigation of Origin of Giant Saturation Magnetization in $\hbox{Fe}_{16}\hbox{N}_{2}$

We present a systematic study to address a longstanding mystery in magnetic materials and magnetism, whether there is giant saturation magnetization in Fe16N2 and why. Experimental results based on sputtered thin film samples are presented. The magnetism of Fe16N2 is discussed systematically from the aspects of material processing, magnetic characterization and theoretical investigation. It is observed that thin films with Fe16N2+Fe8N mixture phases and high degree of N ordering, exhibit a saturation magnetization up to 2.68T at room temperature, which substantially exceeds the ferromagnetism limit based on the traditional band magnetism understanding. From X-ray magnetic circular Dichorism (XMCD) experiment, transport measurement and first-principle calculation based on LDA+U method, it is both experimentally and theoretically justified that the origin of giant saturation magnetization is correlated with the formation of highly localized 3d electron states in this Fe-N system. A large magnetocrystalline anisotropy for such a material is also discussed. Our proposed “cluster+atom” theory provides promising directions on designing novel magnetic materials with unique performances.

GROWTH AND DEPTH-DEPENDENCE OF SATURATION MAGNETIZATION OF IRON NITRIDE THIN FILMS ON MgO SUBSTRATE

We used polarized neutron reflectometry (PNR) to investigate the depth-dependent saturation magnetization (4πMs) of bi-layer structured Fe–N/Fe grown on MgO substrates, which were prepared by a facing target sputtering method followed by a subsequent annealing process to purposely study the N inter-diffusive effect. It is observed that by tuning the Fe layer thickness from 2 nm to 5 nm, the magnetic properties of the resulting product varies substantially. According to X-ray diffraction, an additional peak, indexed to Fe16N2(004) , was developed in the sample with thinner (2 nm) underlayer. Its corresponding PNR study shows a 4πMs of up to 2.82 T towards the substrate interface, which is 14% higher than the known limit ( Fe 65 Co 35 ~ 4πMs = 2.45 T ). We attribute this giant magnetization to the presence of chemically ordered Fe1N2 . We have seen evidence that the high Ms is favorably stabilized due to the lattice misfit. The thickness range is consistent with the strained region of the films. This depth-dependent saturation magnetization analysis can shed a light to help understand the previous magnetization reports by classical magnetometry methods for the samples prepared using the same underlayer.

Thermomagnetic power generation performance of first-order phase transition material Mn1.2Fe0.8P0.4Si0.6

In this paper, we report on the magnetism and the thermomagnetic power generation performance of a first-order phase transition material Mn1.2Fe0.8P0.4Si0.6,which can be used for thermomagnetic power generation that turns heat directly into electricity. The compound is synthesized by using the high-energy ball milling and solid state reaction method. Magnetic measurements show that the compound undergoes a ferromagnetic-to-paramagnetic first-order phase transition at 337 K, accompanied by a giant magnetization change. According to this feature of the material, we design a demonstration device for thermomagnetic power generation, and study the electric current generated by heat induced phase transition. The current increases with the increase of the heat-flow temperature and the mass of material. This study shows that the Mn1.2Fe0.8P0.4Si0.6 compound possesses the high performance of thermomagnetic power generation.

Structural and polarized neutron reflectrometry characterization of Fe16N2thin films with giant saturation magnetization

Structural and polarized neutron reflectrometry characterization of Fe₁₆N₂thin films with giant saturation magnetization

Giant electric field controlled magnetic anisotropy in epitaxial BiFeO3-CoFe2O4 thin film heterostructures on single crystal Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrate

We have deposited self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) thin films on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrates and studied the change in magnetic anisotropy under different strain conditions induced by an applied electric field. After electric field poling, we observed (i) giant magnetization change: magnetization of original CFO phase is three times larger than that of strained one and (ii) magnetic force microscopy line profiles that exhibited significant change in the CFO magnetic domain response in accordance to magnetization-field (M-H) loops. Together, these results demonstrate good control of the magnetic properties of CFO via an electric field induced strain.

Epitaxial high saturation magnetization FeN thin films on Fe(001) seeded GaAs(001) single crystal wafer using facing target sputterings

It was demonstrated that Fe–N martensite (α′) films were grown epitaxially on Fe(001) seeded GaAs(001) single crystal wafer by using a facing target sputtering method. X-ray diffraction pattern implies an increasing c lattice constant as the N concentration increases in the films. Partially ordered Fe16N2 films were synthesized after in situ post-annealing the as-sputtered samples with pure Fe8N phase. Multiple characterization techniques including XRD, XRR, TEM, and AES were used to determine the sample structure. The saturation magnetization of films with pure Fe8N phase measured by VSM was evaluated in the range of 2.0–2.2 T. The post annealed films show systematic and dramatic increase on the saturation magnetization, which possess an average value of 2.6 T. These observations support the existence of giant saturation magnetization in α″-Fe16N2 phase that is consistent with a recent proposed cluster-atom model and the first principles calculation [N. Ji, X. Q. Liu, and J. P. Wang, New J. Phys. 12 063032 (2010)].

N site ordering effect on partially ordered Fe16N2

Partially ordered Fe16N2 thin films have been fabricated on Fe (001)-buffered GaAs (001) single-crystal substrates by a facing target sputtering process. The saturation magnetization has been systematically investigated as a function of N site ordering in partially ordered Fe16N2 thin films, which is found to be increased monotonically with the increase in the N site ordering parameter, reaching up to 2.68 T at high ordering case. A model discussion is provided based on the partial localization of 3d electron states in this material system, which successfully rationalizes the formation of the giant saturation magnetization in chemically ordered Fe16N2. We further demonstrate that the average magnetic moment of partially ordered Fe16N2 sensitively depends on the special arrangement of Fe6N clusters, which is the key to realize high magnetic moment in this material system.