Magnetic Switching Properties Research Articles

Formation of Dewetted Epitaxial Structures of Fe3O4/Fe and Their Magnetic Switching Properties

Herein, it is demonstrated that the solid‐state dewetting of patterned Fe(100) films can lead to the formation of epitaxial heterostructures of Fe3O4 and Fe. Fe3O4 layers can be grown conformally on multiple facets of dewetted Fe patterns, without buckle delamination, creating epitaxial interfaces. The dewetted line patterns show switching behaviors that are indicative of parallel and antiparallel coupling of Fe3O4 and Fe magnetization, when magnetic fields are applied along their long and short axes, respectively. By comparing this behavior with the results of micromagnetic simulations, it is suggested that the anisotropic switching behavior cannot be solely attributed to the shape anisotropy of the dewetted patterns; their interfacial atomic structures should also be considered.

Synthesis and Characterization of a One-Dimensional Malleable Spin-Crossover Polymer Complex Modified by Methoxy Polyethylene Glycol.

A novel one-dimensional malleable spin-crossover (SCO) complex {[Fe(MPEG-trz)3](BF4)2} has been successfully synthesized by molecular self-assembly between 4-amino-1,2,4-triazoles (MPEG-trz) grafted with a long flexible chain methoxy polyethylene glycol (MPEG) and metallic complex Fe(BF4)2•6H2O. The detailed structure information was illustrated by using FT-IR and 1H NMR measurements, while the physical behaviors of the malleable SCO complexes were systematically investigated by using magnetic susceptibility measurements using superconductivity quantum interference device (SQUID) and differential scanning calorimetry (DSC). This new metallopolymer exhibits a remarkable spin crossover transition behavior, between two spin quantum states (Fe2+ ions): high spin (HS) state (quintet state) and low spin (LS) state (singlet state), at a specific critical temperature with a slender hysteresis loop of 1 K. DFT computations revealed the partial rules of HOMO-LUMO energy levels and spin density distributions of different four-position substituted [Fe(1,2,4-triazole)3]2+ derivatives with different length of repeat units in polymer complexes. This can go a step further to depict the spin and magnetic transition behaviors of SCO polymer complexes. Furthermore, the coordination polymers possess an excellent processability due to an outstanding malleability, which can be easily shaped into a polymer film with spin magnetic switching properties.

Multi-susceptible single-phased hexaferrite with significant magnetic switching properties by selectively doping

An effective combustion technique is used to synthesize Sr0.8La0.2Fe12-xCuxO19 (x = 0,1) M-type strontium hexagonal ferrite nanoparticles (SHFNPs). The impact of La and La-Cu substitution on the structural, microstructural, and magnetic characteristics of SHFNPs is scrutinized. The samples are characterized using several experimental techniques, such as x-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and vibrating sample magnetometer (VSM). The obtained results reveal that the single lattice structure of the substituted strontium hexaferrite can be acquired by transforming Fe3+ to Fe2+ on the 2a site. Raman spectroscopy (RS) verifies the formation of all crystallographic sites of hexaferrite. The broadening of 4f2 and 12k peaks indicates the presence of disorder at the crystal sites resulting from the change in the chemical environment after doping with Cu2+ ions. FESEM images reveal flat hexagonal facets of the particle that signify the magneto-plumbite structure. The magnetic results provide high values of both intrinsic coercivity and (BH)max. The obtained data constitute good magnetic characteristics for perpetual magnet applications. Furthermore, the reduced coercivity of the Sr0.8La0.2Fe11CuO19 (SLCHF) sample with high magnetizations can be used to create microwave absorbing and data storage materials.

Enhancement of supercurrent through ferromagnetic materials by interface engineering

Josephson junctions containing ferromagnetic materials exhibit interesting physics and show promise as circuit elements for superconducting logic and memory. For memory applications, the properties of the junction should be controllable by changing the magnetic configuration inside the junction. To achieve good magnetic switching properties, one should choose a soft magnetic material such as NiFe (permalloy); however, NiFe exhibits poor supercurrent transmission in Josephson junctions. In this paper, we put thin layers of Ni on either side of the NiFe and characterize the magnetic behavior and supercurrent transmission properties of the Ni/NiFe/Ni trilayers as a function of Ni and NiFe thicknesses. Using a Ni thickness of 0.4 nm, we find that the magnetic switching behavior of the trilayers is not severely degraded relative to plain NiFe, while the maximum supercurrent in the $\ensuremath{\pi}$ state of the trilayer Josephson junctions is increased by a factor of four relative to that of NiFe junctions. We speculate that the supercurrent enhancement is due to the different spin-dependent transport properties of the Cu/Ni and Cu/NiFe interfaces.

Structure and magnetic transitions along with magnetization switching in nanoparticles of CeCr1-xFexO3 (0 ≤ x ≤ 0.1)

Here, we have investigated the structural, magnetic, and bipolar switching properties in CeCr1-xFexO3 (0 ≤ x ​≤ ​0.1) nanoparticles synthesized by one-step solution combustion method. Rietveld and Raman analysis demonstrate an increase in distortion of orthorhombic structure after substitution of Fe3+ ions due to the rotation/tilting of Cr–O6 octahedra. Besides the Néel transition, TN2 ~260 ​K due to antiferromagnetic (AFM) ordering of Cr3+ in x ​= ​0, a new Néel transition, TN1 above TN2 in x ​> 0 is manifested attributing to the weak antiferromagnetic interaction between Cr3+ and Fe3+ moments. Below the Néel transitions, some interesting magnetic features such as compensation temperature, Tcomp and spin reorientation temperature, TSR are observed. Most importantly, a stable bipolar switching of magnetization by varying the external field is demonstrated for x ​= ​0.06 which could be exploited for its potential use in data storage and magnetic switching based nonvolatile magnetic memory devices.

A Molecular Crystal Shows Multiple Correlated Magnetic and Ferroelectric Switchings

Simultaneous control of the magnetic and electric properties of materials is crucial for their application in next-generation memory and sensor devices. Herein, we report a single-crystal Co(II) co...

Realization of resistive and magnetization switching in sol-gel derived yttrium iron garnet thin films

In this work, large-area ferrite thin films of ferromagnetic yttrium iron garnet (Y3Fe5O12, YIG) were synthesized on Pt/Ti/SiO2/Si (Pt) substrates by a sol-gel method to investigate the resistive and magnetization switching properties. The synthesized YIG thin films acquire a single garnet structure. The Pt/YIG/Pt stack illustrates unipolar resistive switching behavior with excellent switching uniformity, large memory window (102), stable cycle-to-cycle endurance, and good data storage retention (104 s). The ~46% saturation magnetization variation could be realized via the conversion between high and low resistance states by manipulating the electric field. Schottky emission is governed in the high-field region for the high resistance state. Temperature dependence of resistance and magnetization variation confirms that oxygen vacancies conductive filament model and valence state change (Fe2+ and Fe3+) are responsible for the resistive and magnetization switching mechanisms. These results indicate that YIG ferrite based stack is suitable to design the electro-magnetic coupling multifunctional nonvolatile memory devices.

Introducing a thin MnO2 layer in Co3O4-based memory to enhance resistive switching and magnetization modulation behaviors

Nanocrystalline bilayer composite MnO2/Co3O4 thin films were fabricated by a simple chemical solution deposition method to investigate the resistive and magnetization switching properties. Compared with pure Co3O4 thin films device, bilayer MnO2/Co3O4 thin films device exhibits enhancement in resistive switching (RS) and magnetization modulation, such as uniform SET and RESET voltages, stable cycle-to-cycle switching endurance (>2 × 103 cycles), good data retention time (>104 s), and RS induced magnetization switching (∼63%). Through the analysis of fitting current-voltage (I–V) curves and temperature-dependent resistance, it demonstrated that Schottky emission conduction is dominated at high resistance state of the devices. Enhancement in RS performance can be attributed to the growth and dissolution of confined conductive filaments which are composed of Mn atoms and oxygen vacancies, evidenced by temperature dependence and magnetization switching at different resistance states. The physical relevancy between RS and magnetic switching involves in the creation and annihilation of conductive filaments, associated with the reversible conversion of cation valence state (Co2+ and Co3+, Mn ions and Mn atoms). Results suggest that by introducing a thin MnO2 inserting layer, Co3O4 based device shows promising applications for nonvolatile RS memory and multifunctional electromagnetic coupling device.

Effect of glass-removal on the magnetostriction and magnetic switching properties in amorphous FeSiB microwires

Abstract Results on the influence of glass-removal on the magnetostriction, magnetic switching properties and domain wall propagation in amorphous Fe77.5Si17.5B15 microwires are reported. Glass removal releases high thermoelastic stresses originated by the difference in thermal expansion coefficients of glass and metal, which reduces the coercivity, increases the domain wall mobility and decreases the local nucleation fields and their distributions. Evening the distribution of nucleation fields and eliminating the local surface defects due to glass removal increase the field range of single domain wall propagation regime. It was also found that the saturation magnetostriction coefficient significantly decreases after glass removal, which strengthens the impact of the reduced magnetoelastic anisotropy. The effect of glass removal on magnetostriction was previously observed only in Co-rich microwires with small negative magnetostriction. Understanding the factors that control the magnetic switching and domain wall dynamics is of interest for practical applications in sensing, storage and logic devices.

Switching current reduction using MgO cap layer in magnetic tunnel junctions

We investigate the current induced magnetization switching properties in CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with the MgO cap layer. It is found that the spin-transfer-torque induced switching current density is inversely proportional to the thickness of the MgO cap layer. We attribute the origin of this behavior to the change in the effective demagnetizing field and damping factor in the free layer, which is verified by spin-torque ferromagnetic resonance measurements. Our experimental results suggest that the utilization of the MgO-cap layer in the MTJs may be useful for spintronic device designs, such as spin-transfer torque magnetic random access memories and spin torque oscillators.

Structural, Electrical, Magnetic and Resistive Switching Properties of the Multiferroic/Ferroelectric Bilayer Thin Films.

Bi0.8Pr0.2Fe0.95Mn0.05O3/Bi3.96Gd0.04Ti2.95W0.05O12 (BPFMO/BGTWO) bilayer thin films with Multiferroic/Ferroelectric (MF/FE) structures were deposited onto Pt(111)/Ti/SiO2/Si(100) substrates by using the sol-gel method with rapid thermal annealing. The BPFMO/BGTWO thin films exhibited well-saturated ferromagnetic and ferroelectric hysteresis loops because of the electro-magnetic coupling induced by the MF/FE structure. The remnant magnetization (2Mr) and remnant polarization (2Pr) were 4.6 emu/cm3 and 62 μC/cm2, respectively. Moreover, the bipolar I-V switching curves of BPFMO/BGTWO bilayer thin films resistive random access memory (RRAM) devices were discussed, and investigated for LRS/HRS.

Tuning the perpendicular magnetic anisotropy, spin Hall switching current density, and domain wall velocity by submonolayer insertion in Ta/CoFeB/MgO heterostructures

By submonolayer insertion of Au, Pt, or Pd into Ta/CoFeB/MgO/Ta heterostructures, we tune the perpendicular magnetic anisotropy and the coercive field of the ferromagnetic layer. We demonstrate that this has a major influence on the spin Hall switching current density and its dependence on the external magnetic field. Despite a rather small effective spin Hall angle of θSH≈−0.07, we obtain switching current densities as low as 2×1010 A/m2 with a 2 Å Au interlayer. We find that the Dzyaloshinskii-Moriya interaction parameter D is reduced with Au or Pd interlayers, and the perpendicular anisotropy field is reduced by an order of magnitude with the Pd interlayer. The dependence of the switching current density on the current pulse width is quantitatively explained with a domain wall nucleation and propagation model. Interface engineering is thus found to be a suitable route to tailor the current-induced magnetization switching properties of magnetic heterostructures.

Uniform magnetization dynamics of a submicron ferromagnetic disk driven by the spin–orbit coupled spin torque

A simple model of magnetization dynamics in a ferromagnet/doped semiconductor hybrid structure with Rashba spin–orbit interaction (SOI), driven by an applied pulse of the electric field, is proposed. The electric current excited by the applied field is spin-polarized, due to the SOI and therefore it induces the magnetization rotation in the ferromagnetic layer via s-d exchange coupling. Magnetization dynamics dependence on the electric pulse shape and magnitude is analyzed for realistic values of the parameters. We show that it is similar to the dynamics of a damped nonlinear oscillator with the time-dependent frequency proportional to the square root of the applied electric field. The magnetization switching properties of an elliptic magnetic element are examined as a function of the applied field magnitude and direction.

Current-induced magnetization switching in a nano-scale CoFeB-MgO magnetic tunnel junction under in-plane magnetic field

We study current-induced magnetization switching properties of a magnetic tunnel junction with junction diameter of 19 nm and resistance-area product of 6 Ωμm2 in the nanosecond regime with and without in-plane magnetic field. At zero field, for both parallel (P)-to-anti-parallel (AP) and AP-to-P switchings, the probability of switching PSW approaches unity with the increase of pulse voltage duration τP. However, under in-plane magnetic field, PSW for P-to-AP switching starts to saturate at a value lower than unity with increasing τP, while AP-to-P switching remains the same as in the absence of in-plane magnetic field. This in-plane field dependence of PSW can be partially explained by the influence of electric-field modulation of magnetic anisotropy.

Studies on structural, optical, magnetic, and resistive switching properties of doped BiFe1-xCrxO3 thin films

We report the effect of multivalent Cr-ion doping on the structural, optical, magnetic, and resistive switching properties of BiFe1-xCrxO3 (BFCO) thin films (where, 0 ≤ x ≤ 0.15). BFCO thin films were deposited on Pt/TiO2/SiO2/Si (100) substrate using pulsed laser deposition technique. X-ray diffraction and micro-Raman analysis revealed the presence of a secondary phase in BFCO thin films, above 5% Cr doping concentrations. Enhanced magnetization was observed in BFCO films owing to ferromagnetic superexchange interaction between Fe and Cr-ions. X-ray photoelectron spectroscopy measurements revealed the multivalent states of Cr and Fe-ions, where suppression of oxygen vacancies due to Cr-ion doping in BFCO films was discussed based on the defect chemistry viewpoint. Moreover, current conduction and resistive switching properties were studied and the dominant switching mechanism was explained in the light of oxygen vacancies assisted filamentary conduction model.

Ferroic phase transitions and switching properties of modified BiFeO3–SrTiO3 multiferroic perovskites

Ferroelectric (FE), ferromagnetic (FM), and multiferroic phases are low-temperature lattice-deformed or/and spin-ordering phase through structural phase transition. Here, relaxor-FE and parasitic FM structural phase transitions with both ordering temperatures above 180 °C were observed in the A(Zn1/2Ti1/2)O3-modified BiFeO3–SrTiO3 (A = Bi, La) perovskite-structured ternary solid solution ceramics. Their ferroic polarization and magnetization switching properties were also observed at room temperature and demonstrated to be multiferroic compound.

Electric field-induced coexistence of nonvolatile resistive and magnetization switching in Pt/NiO/Nb:SrTiO3 heterostructure

We report the coexistence of nonvolatile resistive and magnetization switching in Pt/NiO/Nb:SrTiO3 heterostructures. These structures exhibit bipolar resistive switching (RS) behavior with multilevel RS characteristics, a maximum RS ratio of 105, and stable endurance properties. Under simple application of voltage pulses, the saturation magnetization of the NiO layer increases by up to three times in the different resistance states. This electrical modulation of both the resistive and magnetization switching properties is attributed to the migration of oxygen vacancies and charge trapping and detrapping at the heterojunction interface. Our results provide a pathway towards the electrical switching of both resistance and magnetization, which is likely to be useful for RS and magnetic multifunctional device applications.

Current-Induced Magnetization Switching of CoFeB/Ta/[Co/Pd (Pt)]-Multilayers in Magnetic Tunnel Junctions With Perpendicular Anisotropy

We investigate magnetic properties of CoFeB/Ta/[Co/Pd (Pt)] multilayers and properties of magnetic tunnel junctions (MTJs) with the structures as a recording layer. CoFeB/Ta/[Co/Pd] multilayer shows a lower damping constant $\alpha $ than that of CoFeB/Ta/[Co/Pt] multilayer. We evaluate current-induced magnetization switching (CIMS) properties of the MTJs with CoFeB/Ta/[Co/Pd (Pt)] multilayers with the junction diameter of 15 (13) nm that show similar thermal stability factor. CIMS is observed for the MTJ with a CoFeB/Ta/[Co/Pd] multilayer at zero magnetic field, whereas it is observed for the MTJ with the CoFeB/Ta/[Co/Pt] multilayer only in the presence of an external field.

Magnetic switching of nanoscale antidot lattices.

We investigate the rich magnetic switching properties of nanoscale antidot lattices in the 200 nm regime. In-plane magnetized Fe, Co, and Permalloy (Py) as well as out-of-plane magnetized GdFe antidot films are prepared by a modified nanosphere lithography allowing for non-close packed voids in a magnetic film. We present a magnetometry protocol based on magneto-optical Kerr microscopy elucidating the switching modes using first-order reversal curves. The combination of various magnetometry and magnetic microscopy techniques as well as micromagnetic simulations delivers a thorough understanding of the switching modes. While part of the investigations has been published before, we summarize these results and add significant new insights in the magnetism of exchange-coupled antidot lattices.

Micromagnetic Structure of Co Stripe Arrays With Tuned Anisotropy

An interwire magnetostatic coupling is one of the most important effects in the micro- and nanowire arrays, because of it strongly influences on the magnetization switching, spin-wave dynamics and magneto-transport properties. Manipulation of the magnetostatic coupling is possible not only by variation of a dimension of nanowires and geometry of arrays, but also by changing the magnetic anisotropy. In this paper, we report on an investigation of the magnetic behavior of arrays consisting of finite number of Co microstripes with two mutually perpendicular induced anisotropies. We have studied an effect of the interwire coupling on the switching field of magnetization and analyzed the domain structure of the arrays under an impact of the induced anisotropies.