Large Room-temperature Magnetoresistance Research Articles

Electrically Controlled All-Antiferromagnetic Tunnel Junctions on Silicon with Large Room-Temperature Magnetoresistance.

Antiferromagnetic (AFM) materials are a pathway to spintronic memory and computing devices with unprecedented speed, energy efficiency, and bit density. Realizing this potential requires AFM devices with simultaneous electrical writing and reading of information, which are also compatible with established silicon-based manufacturing. Recent experiments have shown tunneling magnetoresistance (TMR) readout in epitaxial AFM tunnel junctions. However, these TMR structures are not grown using a silicon-compatible deposition process, and controlling their AFM order required external magnetic fields. Here are shown three-terminal AFM tunnel junctions based on the noncollinear antiferromagnet PtMn3, sputter-deposited on silicon. The devices simultaneously exhibit electrical switching using electric currents, and electrical readout by a large room-temperature TMR effect. First-principles calculations explain the TMR in terms of the momentum-resolved spin-dependent tunneling conduction in tunnel junctions with noncollinear AFM electrodes.

High room temperature magnetoresistance in La0.9Sr0.1Mn1-yZnyO3 epitaxial films

Developing large room temperature magnetoresistance materials has been a major hotspot for a few last decades due to its importance in the practical applications in magneto-resistive random access memory, and it remains a challenge. Here, La0.9Sr0.1Mn1-yZnyO3 (LSMZO) films have been grown on SrTiO3 substrates by magnetron sputtering, showing excellent quality of epitaxy. Upon increasing Zn content, the reduction of Curie temperature (TC) and metal-insulator transition temperature (TMI) is observed, accompanied by the increase of coercive field and room-temperature resistivity. Analysis on the fraction of Mn3+ and Mn4+ indicates that Zn2+ substitution at Mn site results in a higher Mn4+ fraction departing from the optimum value and hence a weaker double-exchange interaction by replacing more Mn3+. Besides that, ionic radius mismatch induced internal strain and substrate induced tensile strain also play a part. Most significantly, the enhanced magnetic disorder gives rise to an increase of intrinsic magnetoresistance around room temperature in LSMZO (y = 10%) film, and a large magnetoresistance of 18.4% is obtained under 0.3 T at 280 K in this sample. Our research provides a simple and effective approach to achieve a large room temperature magnetoresistance in Mn site doped manganite epitaxial films.

Room-temperature magnetoresistance in an all-antiferromagnetic tunnel junction.

Antiferromagnetic spintronics1-16 is a rapidly growing field in condensed-matter physics and information technology with potential applications for high-density and ultrafast information devices. However, the practical application of these devices has been largely limited by small electrical outputs at room temperature. Here we describe a room-temperature exchange-bias effect between a collinear antiferromagnet, MnPt, and a non-collinear antiferromagnet, Mn3Pt, which together are similar to a ferromagnet-antiferromagnet exchange-bias system. We use this exotic effect to build all-antiferromagnetic tunnel junctions with large nonvolatile room-temperature magnetoresistance values that reach a maximum of about 100%. Atomistic spin dynamics simulations reveal that uncompensated localized spins at the interface of MnPt produce the exchange bias. First-principles calculations indicate that the remarkable tunnelling magnetoresistance originates from the spin polarization of Mn3Pt in the momentum space. All-antiferromagnetic tunnel junction devices, with nearly vanishing stray fields and strongly enhanced spin dynamics up to the terahertz level, could be important for next-generation highly integrated and ultrafast memory devices7,9,16.

Room-temperature magnetoresistive and magnetocaloric effect in La1−xBaxMnO3 compounds: Role of Griffiths phase with ferromagnetic metal cluster above Curie temperature

The evolution of the Griffiths phase (GP) with a ferromagnetic metal (FMM) cluster above the Curie temperature (TC) and its effect on the magnetic properties, electrical transport, magnetoresistance (MR), and magnetocaloric effect (MCE) is studied comprehensively, using bulk compounds of La1−xBaxMnO3 (0.15 ≤ x ≤ 0.25) with different lattice distortions but with the same structural symmetry and space group. These La1−xBaxMnO3 samples show ferromagnetic transition at TC increasing from 229 K for x = 0.15–300 K for x = 0.25, in addition to the presence of GP with FMM clusters in the paramagnetic (PM) region, which have been confirmed by the combination of magnetization (susceptibility) measurements, the GP theory, and electron paramagnetic resonance technology. With increasing the Ba2+ ion doping, GP temperature (TG) and TC of La1−xBaxMnO3 are increased, and the GP regime is strengthened. The GP ratio in the PM region reached 27.7% for the sample with x = 0.20. The resistivity decreases and the FMM phase increases with increasing x from 0.15 to 0.25, which can be explained by the decrease in the bandgap (Eg) and the enhancement of the double-exchange effect. Remarkably, large room-temperature MR (∼44.7%) can be observed in the sample with x = 0.25 under 60 kOe, which is related to the presence of the GP regime. Furthermore, the MCE is also affected by the GP regime, and it is deduced that the magnetic transition is of second order. The value of magnetic entropy change (|ΔSM|) reaches 3.04 J/kg K near room temperature for the sample with x = 0.25 under 50 kOe. This value is associated with a relative cooling power (RCP) of 248.1 J/kg. For the sample with x = 0.15, the value of RCP reaches 307.6 J/kg under 50 kOe. The discovery of the MR and MCE near room temperature is of great significance from the practical application of perovskite manganites in magnetic sensors and magnetic refrigerants.

Facile magnetoresistance adjustment of graphene foam for magnetic sensor applications through microstructure tailoring

Abstract Graphene foam is becoming a material of choice for magnetoelectronic devices due to its large, linear and unsaturated room temperature magnetoresistance. However, the magnetoresistance of graphene foam is not as large as that of monolayer graphene. Herein, we describe how magnetoresistance ~ 100% was detected at room temperature under a magnetic field of 5 T that is comparable to the magnetoresistance in monolayer graphene; the highest magnetoresistance of ~158% was detected at 5 K under a magnetic field of 5 T. Unlike monolayer graphene, graphene foam is far more comfortable with producing in gram scale and utilizing in magnetoelectronic devices.

Exchange bias and large room temperature magnetoresistance in ion beam-synthesized Co nanoparticles in SiO2

Magnetic nanogranular materials have shown promising magnetic and electron transport properties, offering key advantages for a range of applications from spintronics components to magnetic field sensors. In this paper, the properties of Co nanoparticles synthesized using low-energy ion implantation and electron beam annealing (EBA) on SiO2 were investigated. EBA leads to the growth of crystalline face-centred cubic Co nanoparticles from small nanoparticles within a Co-rich region in the near surface. The as-implanted and EBA samples are ferromagnetic with Curie temperatures above 300 K. The saturated magnetic moment per implanted Co atom was measured to be as high as 4.25 ± 0.5 μB. The moment per Co atom decreases and approaches that of bulk Co with increased EBA time. This suggests that there may be a ferromagnetic Co1-xSixOy phase that has not been previously reported. An exchange bias is observed and proposed to arise from a thin antiferromagnetic CoO layer surrounding the Co nanoparticles. We find a room temperature magnetoresistance as high as 22.8% at 8 T with linear behaviour above ~ 3 T. The linear magnetoresistance is likely to be due to a geometric magnetoresistance that is observed in inhomogeneous nanomaterials containing metallic nanoparticles in a semiconducting matrix. Thus, EBA leads to Co nanoparticles that are expected to be electronically spin polarized but there is no evidence for spin-dependent tunnelling. These unique characteristics could provide the base for novel devices.

Large room temperature magnetoresistance in La0.9Sr0.1MnO3 thin films

Epitaxial La0.9Sr0.1MnO3 thin films were crystallized using post-annealing after deposited at room temperature, and the effect of sputtering pressure on the structural, magnetic and electrical properties was investigated. It is interesting to note that the out-of-plane lattice parameter decreases with decreasing sputtering pressure, which is attributed to the reduction of Mn3+/Mn4+ ratio. Differing from the corresponding bulk material, all the films show metal-insulator (MI) transition with a significantly enhanced Curie temperature (TC). And the film deposited at 1.0 Pa shows the maximum TMI and TC resulted from the strongest double exchange interaction. Most significantly, the largest magnetoresistance around room temperature (−53% at 3 T and 295 K) is also observed in this film, showing great potential in application.

Large Magnetoresistance in Silicon at Room Temperature Induced by Onsite Coulomb Interaction

Magnetoresistance (MR), as a key property in magnetic‐field sensing and magnetic storage, has been a long‐term focus. In particular in silicon, which is the mainstream semiconductor of information technology, the MR phenomenon has attracted a lot of attention because of its fundamental interest and broad application potential. Here, a large MR in silicon, which is associated with impurity onsite Coulomb interaction and space charge limited current (SCLC), is observed at room temperature. In the presence of SCLC, delocalization of electrons in doubly occupied traps with a strong onsite Coulomb interaction leads to an S‐shape negative differential conductance (SNDC). A large room temperature MR (>103% at 0.05 T) appears around the SNDC region. These findings will help to design high‐performance silicon‐based magnetic device (e.g., magnetic switch devices, magnetic logic devices) and pave the way for magnetoelectronics in silicon.

Theory of magnetoresistance of organic molecular tunnel junctions with nonmagnetic electrodes

Large room-temperature magnetoresistance observed for devices composed of self-assembled monolayers of different oligophenylene thiols sandwiched between gold contacts has recently been reported [Z. Xie, S. Shi, F. Liu, D. L. Smith, P. P. Ruden, and C. D. Frisbie, ACS Nano 10, 8571 (2016)]. The transport mechanism through the organic molecules was determined to be nonresonant tunneling. To explain this kind of magnetoresistance, we develop an analytical model based on the interaction of the tunneling charge carrier with an unpaired charge carrier populating a contact-molecule interface state. The Coulomb interaction between carriers causes the transmission coefficients to depend on their relative spin orientation. Singlet and triplet pairing of the tunneling and the interface carriers thus correspond to separate conduction channels with different transmission probabilities. Spin relaxation enabling transitions between the different channels, and therefore tending to maximize the tunneling current for a given applied bias, can be suppressed by relatively small magnetic fields, leading to large magnetoresistance. Our model elucidates how the Coulomb interaction gives rise to transmission probabilities that depend on spin and how an applied magnetic field can inhibit transitions between different spin configurations.

Self-magnetism induced large magnetoresistance at room temperature region in graphene nanocrystallited carbon film

We report large positive magnetoresistance (MR) of over 12% at 273 K in graphene nanocrystallited pure carbon film. MR behaviors at different temperatures implied that low temperature MR was from carrier diffusive scattering and room temperature MR was from spin arrangement effect. Temperature dependences of the film resistance and magnetization recognized that as temperature decreased from 300 to 200 K, transitions occurred on the electrical transporting process from conductive mode to semi-conductive mode, and the nanocrystallited structure showed competition of ferromagnetic and antiferromagnetic interactions. The large room temperature MR was ascribed to the ferromagnetic order of spin magnetic moment arrangement at the of graphene layer edges.

Hydrogen Treatment for Superparamagnetic VO2 Nanowires with Large Room-Temperature Magnetoresistance.

One-dimensional (1D) transition metal oxide (TMO) nanostructures are actively pursued in spintronic devices owing to their nontrivial d electron magnetism and confined electron transport pathways. However, for TMOs, the realization of 1D structures with long-range magnetic order to achieve a sensitive magnetoelectric response near room temperature has been a longstanding challenge. Herein, we exploit a chemical hydric effect to regulate the spin structure of 1D V-V atomic chains in monoclinic VO2 nanowires. Hydrogen treatment introduced V(3+) (3d(2) ) ions into the 1D zigzag V-V chains, triggering the formation of ferromagnetically coupled V(3+) -V(4+) dimers to produce 1D superparamagnetic chains and achieve large room-temperature negative magnetoresistance (-23.9 %, 300 K, 0.5 T). This approach offers new opportunities to regulate the spin structure of 1D nanostructures to control the intrinsic magnetoelectric properties of spintronic materials.

Ferromagnetic Multilayers: Magnetoresistance, Magnetic Anisotropy, and Beyond

Obtaining highly sensitive ferromagnetic, FM, and nonmagnetic, NM, multilayers with a large room-temperature magnetoresistance, MR, and strong magnetic anisotropy, MA, under a small externally applied magnetic field, H, remains a subject of scientific and technical interest. Recent advances in nanofabrication and characterization techniques have further opened up several new ways through which MR, sensitivity to H, and MA of the FM/NM multilayers could be dramatically improved in miniature devices such as smart spin-valves based biosensors, non-volatile magnetic random access memory, and spin transfer torque nano-oscillators. This review presents in detail the fabrication and characterization of a few representative FM/NM multilayered films—including the nature and origin of MR, mechanism associated with spin-dependent conductivity and artificial generation of MA. In particular, a special attention is given to the Pulsed-current deposition technique and on the potential industrial applications and future prospects. FM multilayers presented in this review are already used in real-life applications such as magnetic sensors in automobile and computer industries. These material are extremely important as they have the capability to efficiently replace presently used magnetic sensors in automobile, electronics, biophysics, and medicine, among many others.

Large room-temperature magnetoresistance in epitaxial La0.7Ca0.25Sr0.05MnO3 thin films prepared by sol–gel method

Epitaxial La0.7Ca0.25Sr0.05MnO3 (LCSMO) thin films were successfully prepared on LaAlO3 (LAO) substrates by ordinary aqueous sol–gel method. X-ray diffraction result shows that the films have perfect crystalline orientation. The HRTEM results confirm that the films have epitaxial structure and the interface is very sharp and no misfit dislocations. The selected area electron diffraction patterns and fast Fourier transformation patterns mean that there exist three domains in the thin film. The single-particle spin-flip excitations are dominant for the metallic ferromagnets in low-temperature range. In paramagnetic range, the temperature dependence of resistivity can be well analyzed using a small polaron theory. The magnetoresistance value for the films reaches maximum about 65 % with 7 T magnetic field at 285 K which is promising for highly demanding applications. The conventional sol–gel method produces the lanthanum manganese oxide thin films with excellent epitaxial structure and large magnetoresistance at room temperature which can be used for either fundamental studies or real applications. The conventional sol–gel method produces the lanthanum manganese oxide thin films with excellent epitaxial structure and giant magnetoresistance at room temperature which can be used for either fundamental studies or real applications.

Impact ionization and large room-temperature magnetoresistance in micron-sized high-mobility InAs channels

We report on hot electron induced impact ionization and large room-temperature magnetoresistance (MR) in micron-sized channels of $n$-type high-mobility InAs $(\ensuremath{\mu}=3.3{\mathrm{m}}^{2}{\mathrm{V}}^{\ensuremath{-}1}{\mathrm{s}}^{\ensuremath{-}1}$ at $T=300\mathrm{K})$: the MR reaches values of up to 450% in magnetic fields of 1 T and applied voltages of \ensuremath{\sim}1 V and is weakly dependent on temperature. We present Monte Carlo simulations of the hot electron dynamics to account for the large MR and its dependence on the sample geometry and applied electric and magnetic fields. Our work demonstrates that the impact ionization of electrons at room temperature, under small applied magnetic fields (1 T) and small voltages (1 V), can provide an extremely sensitive mechanism for controlling the electrical resistance of high-mobility semiconductors.

Organic magnetoresistance from deep traps

We predict that singly occupied carrier traps, produced by electrical stress or irradiation within organic semiconductors, can cause spin blockades and the large room-temperature magnetoresistance known as organic magnetoresistance. The blockade occurs because many singly occupied traps can only become as doubly occupied in a spin-singlet configuration. Magnetic-field effects on spin mixing during transport dramatically modify the effects of this blockade and produce magnetoresistance. We calculate the quantitative effects of these traps on organic magnetoresistance from percolation theory and find a dramatic nonlinear dependence of the saturated magnetoresistance on trap density, leading to values ∼20%, within the theory's range of validity.

GIANT MAGNETO-ELECTROLUMINESCENCE FROM HYBRID SPIN-ORGANIC LIGHT EMITTING DIODES

An important application that may boost the use of magnetic-field controlled organic devices is significant magnetically modulated electroluminescence (MEL) at room temperature (RT). Whereas inorganic magnetic tunnel junctions show RT magneto-resistance (MR)> 80%, these devices do not exhibit electroluminescence. In contrast, organic light-emitting diodes (OLED) show substantive electroluminescence. Alas, at RT both organic spin valves and spin-OLEDs have shown rather small MR and MEL. We report here a hybrid organic/inorganic magnetic-field controlled device (h-OLED) which comprises of an inorganic magnetic tunnel junction with large room temperature MR, and OLED having efficient electroluminescence. At RT the h-OLED devices exhibit up to 80% giant MEL in the red, green, and blue spectral ranges. Moreover studies of "white" h-OLED devices show a surprising magnetic-field controlled color manipulation. The h-OLED devices may open a new avenue in the application of multifunctional organic displays.

Resistivity dependence of magnetoresistance in Co/ZnO films

We report the dependence of magnetoresistance effect on resistivity (ρ) in Co/ZnO films deposited by magnetron sputtering at different sputtering pressures with different ZnO contents. The magnitude of the resistivity reflects different carrier transport regimes ranging from metallic to hopping behaviors. Large room-temperature magnetoresistance greater than 8% is obtained in the resistivity range from 0.08 to 0.5 Ω · cm. The magnetoresistance value decreases markedly when the resistivity of the films is less than 0.08 Ω · cm or greater than 0.5 Ω · cm. When 0.08 Ω · cm < ρ < 0.5 Ω · cm, the conduction contains two channels: the spin-dependent tunneling channel and the spin-independent second-order hopping (N = 2). The former gives rise to a high room-temperature magnetoresistance effect. When ρ > 0.5 Ω · cm, the spin-independent higher-order hopping (N > 2) comes into play and decreases the tunneling magnetoresistance value. For the samples with ρ < 0.08 Ω · cm, reduced magnetoresistance is mainly ascribed to the formation of percolation paths through interconnected elongated metallic Co particles. This observation is significant for the improvement of room-temperature magnetoresistance value for future spintronic devices.

Significant magneto-resistive effects in boron carbide thin films

We have found large room temperature magneto-resistance in boron carbides fabricated via electron-induced cross-linking of icosahedral closo-1,2-dicarbadodecaborane (ortho-carborane; 1,2-B10C2H12) in the presence of the aromatic compound 1,4-diaminobenzene (DAB). X-ray photoemission spectroscopy confirms that the electron beam irradiation leads to site-specific cross-linking of the ortho-carborane, with cross-linking between B sites non-adjacent to icosahedral carbon sites on the carborane moiety, and carbon sites on the diaminobenzene moiety. The I–V curves, as a function of external magnetic field, demonstrate that significant room temperature negative magneto-resistance (>50%) is possible in the resulting dielectric thin films. Inclusion of 1,4-diaminobenzene (DAB) is not essential for significant negative magneto-resistance, as crosslinking of ortho-carborane (1,2-B10C2H12 ) results in large negative magneto-resistance, over 100%, depending on bias voltage.

Large positive room temperature magnetoresistance in nanogranular FeCo–Si–N thin films

A large positive room temperature magnetoresistance (MR) up to ~30% at 50kOe was obtained in nanogranular FeCo–Si–N thin film prepared by magnetron sputtering. The quasi-linear dependence of MR on the magnetic field is observed for the fields above 20kOe. The properties of the films depend on both the nonmagnetic component volume and film thickness. To achieve high MR, a proper Si–N content and a critical film thickness are required. The large positive MR may result from the combination of geometric effect as well as spin-dependent scattering. The FeCo–Si–N films with pronounced MR and linear MR-H behavior can be good candidates for future magnetoelectric devices.

Room temperature low field magnetoresistance in Sr2FeMoO6/ZnxFe1−xFe2O4 composites

Double perovskite Sr2FeMoO6/ZnxFe1−xFe2O4 (SFMO/ZFO) composite systems with varying zinc content in nanosized zinc ferrite were synthesized. Composites have been prepared by two phase sintering process of limited intermixing of the SFMO calcined powder and ZFO nanoparticles. The structural analysis confirms the coexistence of both the phases in the composites and revealed that the agglomerated ZFO nanoparticles segregated at the grain boundaries. It was found that the inclusion of low ZFO content (2 wt. %) increases the resistivity, magnetization, and low field magnetoresistance (LFMR), whereas it further decreases with increasing ZFO content. A large room-temperature tunnelling magnetoresistance (Δρ/ρ0) ratio 4.83% and 6.90% was observed for pristine SFMO and SFMO/ZFO (x = 0.7) composite samples respectively at low magnetic field of 2 kOe, which is 1.42 times larger than pure SFMO sample. The enhanced LFMR is highly desirable for room temperature magneto resistive applications.