Ferromagnetism In Mn Research Articles

Stabilization of ferromagnetism in Mn doped ZnO with C co-doping

We present a method for stabilizing ferromagnetism in Mn doped ZnO. We find that Mn doped ZnO show anti-ferromagnetic order in the absence of additional carriers. When Mn doped ZnO is co-doped with C atom at O sites ferromagnetic state gets stabilized. The C doping creates holes which leads to stabilization of ferromagnetic state via hole mediated double exchange mechanism.

Ferromagnetism in Mn and Sb co-doped ZnO films

Zn0.99Mn0.01O and Zn0.985(Mn0.01,Sb0.005)O thin films were prepared on sapphire(0001) by reactive radio-frequency (rf) magnetron sputtering.Zn0.99Mn0.01O showed no obvious ferromagnetic behavior whileZn0.985(Mn0.01, Sb0.005)O exhibited robust ferromagnetic signals with a saturation magnetization of0.92 μB/Mn2+,and Zn0.985(Mn0.01, Sb0.005)O film grown in an oxygen rich condition exhibited a larger saturation magnetization of1.76 μB/Mn2+. The results are most consistent with the bound magnetic polaron model, in whichlocalized p-type defects mediate the ferromagnetic ordering.

Observation of room temperature ferromagnetism in Mn–Fe doped ZnO

A room temperature ferromagnetic Fe doped ZnO bulk sample has been synthesized by co-doping 2 at% Mn with 2 at% Fe in ZnO. The final firing temperature for the preparation of the Zn0.96Mn0.02Fe0.02O sample is the same as the final firing temperature for the preparation of the Zn0.98Mn0.02O sample and in this case it is found to be 490 °C. It has been found that room temperature ferromagnetism in Zn0.96Mn0.02Fe0.02O is a factor of 1.6 times more than that observed in Zn0.98Mn0.02O samples. The size of the saturation magnetic field for the Zn0.96Mn0.02Fe0.02O sample is, however, only a factor of 7 times more than that observed for nanocrystalline undoped ZnO.

High Temperature Ferromagnetism in Mn Based Multilayers of Wide Gap Semiconductors: Mn/ZnO and Mn/SnO2: The Role of Interfaces

High Temperature Ferromagnetism in Mn Based Multilayers of Wide Gap Semiconductors: Mn/ZnO and Mn/SnO2: The Role of Interfaces

Room temperature ferromagnetism in Mn- and Fe-doped indium tin oxide thin films

Undoped and transition-metal doped indium tin oxide films have been grown by pulsed laser deposition technique, on single crystalline c-plane (0001) and r-plane (1102) sapphire substrates maintained at 500–850°C. Magnetization measurements of films deposited at different temperatures indicate that ferromagnetism appears for deposition temperatures, Tdep>600°C, with the highest moment for films deposited around 750°C. Qualitative different ferromagnetic behavior has been observed at room temperature in Fe- and Mn-doped thin films. The stable, hysteretic ferromagnetism of the Fe-doped films is due to the presence of magnetite, as seen in transmission Mössbauer spectra. The Mn-doped films show anhysteretic ferromagnetism which decays over time. It is somehow intrinsic, but not due to the Mn ions, which remains paramagnetic down to 4K. No anomalous Hall effect is observed.

Surface effects on the energetic and spintronic properties of InP nanowires diluted with Mn: First-principles calculations

First-principles calculations have been used to investigate the impurity stability and the magnetic properties of Mn doped InP nanowires. The results reveal that the surface of the nanocrystals play a fundamental role on the impurity stability and on the magnetic properties of InP nanowires diluted with Mn. The formation energy of pairs of Mn impurities in unpassivated nanowires are lower than that of the bulk InP. Most of the Mn pair configurations present FM coupling and they prefer to be inside the nanowire and not on the surface. The origin of the ferromagnetic interaction in the nanowire is different from that of the bulk, and the ferromagnetic coupling is energetically more stable than the ferromagnetism in Mn doped bulk InP, making this nanostructure promising for spintronic applications.

Tuning the ferromagnetism in Mn–Zn–O by intrinsic defects

In this work we employ density-functional theory (DFT) within the generalized-gradientapproximation (GGA) to study the structural and electronic properties of Mn-doped ZnOin the presence and absence of vacancies. We find that pure Mn-doped ZnO exhibitsanti-ferromagnetic behaviour for Mn concentrations smaller than 8.3%. We also show thatoxygen vacancies in Mn-doped ZnO favour anti-ferromagnetism, whereas Zn vacanciesstabilize the ferromagnetic behaviour.

Room temperature ferromagnetism in Mn+-implanted Si nanowires

Room temperature ferromagnetism of Mn+-implanted Si nanowires (NWs) has been discovered. The saturation magnetization was found to increase with the Mn concentration. Healing the damages in crystallinity at 600°C led to an increase in magnetization, while the ferromagnetism disappeared upon annealing at 800°C as Mn atoms segregated to the surface of NWs. The results indicate that Mn+-implanted Si NWs are potentially useful for nanoscale spintronics applications.

Ferromagnetism in Mn doped half-Heusler NiTiSn: Theory and experiment

In this letter, the authors show by ab initio density functional calculations and experiments that Mn doped semiconducting half-Heusler compound NiTiSn can exhibit room-temperature ferromagnetism. Curie temperatures were calculated by Monte Carlo simulations using calculated Heisenberg exchange parameters in an ab initio Green’s function approach. The calculated temperature exceeds room temperature for a Mn doping concentration of 22%. Magnetic measurements confirm the presence of possible intrinsic ferromagnetism in these systems. This brings up the possibility of considering this system as a potential candidate for use in room-temperature spintronic devices.

Structural and magnetic properties of manganese and phosphorus codoped ZnO films on (0001) sapphire substrates

ZnO films doped with manganese (Mn) and phosphorus (P) are grown on (0001) sapphire substrates by pulsed laser deposition at different temperatures and oxygen pressures. The structural and magnetic properties of the codoped ZnO films are carefully investigated. Experimental results demonstrate that p-type conduction is necessary for the observation of ferromagnetism in Mn+P codoped ZnO films at room temperature. A distinct aging effect is observed, which is likely due to the instability of p-type conduction of Mn+P codoped ZnO films.

On the room temperature ferromagnetism of Mn doped ZnO

Room temperature ferromagnetism was observed in polycrystalline samples of Mn doped ZnO synthesized by low temperature solid-state reaction of MnO 2 and ZnO. Co-doping it with Li did not improve its ferromagnetic characteristics. By studying the products obtained by reacting MnO 2 and ZnO, using simple experimental techniques like XRD analysis and DC magnetization, we show that the observed room temperature ferromagnetism in Mn doped ZnO can be attributed to the substitutional incorporation of Mn at Zn-sites rather than due to the formation of segregated secondary phases.

No ferromagnetism in Mn doped ZnO semiconductors

Polycrystalline Zn 1 − x Mn x O was synthesized by co-precipitation method with xvarying between 0.01 and 0.10. Although X-ray diffraction patterns show a typical würtzite structure with no additional peaks for all samples, Raman spectroscopy indicates the appearance of an additional mode in correlation with the absorption edge shift observed by UV–Vis spectroscopy and which is an indicator for incorporation of Mn ions into the ZnO matrix. The magnetic properties have been studied by both EPR spectroscopy and SQUID magnetometry. Their temperature dependence follows a Curie law indicating a typical paramagnetic behavior for x ⩽ 0.05 and no indication of ferromagnetism nor antiferromagnetism.

Structure and ferromagnetism of Mn + ion-implanted ZnO thin films on sapphire

Slow Positron Implantation Spectroscopy (SPIS), based on the generation, implantation and subsequent annihilation of mono-energetic positrons in a sample, has been used to study depth dependent vacancy-type damage in three ZnO films grown by pulsed laser deposition on c-plane sapphire. Doping was achieved by implantation of 250 keV Mn + ions at 300 ∘C with three different fluences— 10 16, 3×10 16, and 6×10 16 cm −2, and subsequent thermal annealing in air. Evolution of the open volume damage, its depth distribution, and the magnetic behavior was investigated by SPIS and Magnetic Force Microscopy. No indication of magnetic domain formation was found in any of the three films after implantation and the first annealing at 500 ∘C, whereas after the second annealing at 750 ∘C the two samples having the higher fluence showed stripe-like magnetic domains.

Ferromagnetism in Mn and Cr doped GaN by thermal diffusion

Doping of magnetic element Mn and Cr in GaN was achieved by thermal diffusion. The conductivity of the samples, which were all n-type, did not change significantly after the diffusion doping. X-ray diffraction measurements revealed no secondary phase in the samples. Experiments using superconducting quantum interference device (SQUID) showed that the samples were ferromagnetic at 5 and 300 K, implying the Curie temperature to be around or over 300 K, despite their n-type conductivity.

Room-temperature ferromagnetism in Mn-doped SnO2 diluted magnetic semiconductor

Using the solid_state diffusion method, a series of Sn1-xMnxO2(x=002—006) diluted magnetic semiconductors(DMSs) are fabricated.By u sing x_ray diffraction(XRD) measurements and Fouier transform infrared spectrosc opic(NEXUS870) analyses,a uniform Mn distribution in the SnO2 is conf irmed. An obvious ferromagnetism in Mn_doped SnO2 DMS at room temperature is f ound and the ferromagnetism is weak with the increase of Mn concentration.

Absence of ferromagnetism in Mn- and Co-doped ZnO

Following the theoretical predictions of ferromagnetism in Mn- and Co-doped ZnO, several workers reported ferromagnetism in thin films as well as in bulk samples of these materials. While some observe room-temperature ferromagnetism, others find magnetization at low temperatures. Some of the reports, however, cast considerable doubt on the magnetism of Mn- and Co-doped ZnO. In order to conclusively establish the properties of Mn- and Co-doped ZnO, samples with 6 percent and 2 percent dopant concentrations, have been prepared by the low-temperature decomposition of acetate solid solutions. The samples have been characterized by x-ray diffraction, EDAX and spectroscopic methods to ensure that the dopants are substitutional. All the Mn- and Co-doped ZnO samples (prepared at 400 deg C and 500 deg C) fail to show ferromagnetism. Instead, their magnetic properties are best described by a Curie-Weiss type behavior. It appears unlikely that these materials would be useful for spintronics, unless additional carriers are introduced by some means.

Synthesis of Colloidal Mn2+: ZnO Quantum Dots and High‐Tc Ferromagnetic Nanocrystalline Thin Films.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of colloidal Mn2+:ZnO quantum dots and high-TC ferromagnetic nanocrystalline thin films.

We report the synthesis of colloidal Mn(2+)-doped ZnO (Mn(2+):ZnO) quantum dots and the preparation of room-temperature ferromagnetic nanocrystalline thin films. Mn(2+):ZnO nanocrystals were prepared by a hydrolysis and condensation reaction in DMSO under atmospheric conditions. Synthesis was monitored by electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. Zn(OAc)(2) was found to strongly inhibit oxidation of Mn(2+) by O(2), allowing the synthesis of Mn(2+):ZnO to be performed aerobically. Mn(2+) ions were removed from the surfaces of as-prepared nanocrystals using dodecylamine to yield high-quality internally doped Mn(2+):ZnO colloids of nearly spherical shape and uniform diameter (6.1 +/- 0.7 nm). Simulations of the highly resolved X- and Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic susceptibilities, confirmed that the manganese is substitutionally incorporated into the ZnO nanocrystals as Mn(2+) with very homogeneous speciation, differing from bulk Mn(2+):ZnO only in the magnitude of D-strain. Robust ferromagnetism was observed in spin-coated thin films of the nanocrystals, with 300 K saturation moments as large as 1.35 micro(B)/Mn(2+) and T(C) > 350 K. A distinct ferromagnetic resonance signal was observed in the EPR spectra of the ferromagnetic films. The occurrence of ferromagnetism in Mn(2+):ZnO and its dependence on synthetic variables are discussed in the context of these and previous theoretical and experimental results.

Ferromagnetism in Mn/X/Si (X = B, BN, B4C, SiC) trilayers

The ferromagnetism in Mn(6 nm)/X(0.5 nm)/Si(6 nm) (X = B, BN, B4C,SiC) trilayers was investigated. The as-deposited trilayers did not exhibit ferromagnetism, but the trilayers annealed around 700 K did exhibit ferromagnetism at 77 K. The annealed Mn/B4C/Si trilayer has a Curie temperature above 300 K. The Mn/B/Si, Mn/BN/Si and Mn/SiC/Si trilayers have Curie temperatures around 260 K.

Ferromagnetism in Mn-doped GaAs due to substitutional-interstitial complexes

While most calculations on the properties of the ferromagnetic semiconductor GaAs:Mn have focussed on isolated Mn substituting the Ga site (Mn$_{Ga}$), we investigate here whether alternate lattice sites are favored and what the magnetic consequences of this might be. Under As-rich (Ga-poor) conditions prevalent at growth, we find that the formation energies are lower for Mn$_{Ga}$ over interstitial Mn (Mn$_i$).As the Fermi energy is shifted towards the valence band maximum via external $p$-doping, the formation energy of Mn$_i$ is reduced relative to Mn$_{Ga}$. Furthermore, under epitaxial growth conditions, the solubility of both substitutional and interstitial Mn are strongly enhanced over what is possible under bulk growth conditions. The high concentration of Mn attained under epitaxial growth of p-type material opens the possibility of Mn atoms forming small clusters. We consider various types of clusters, including the Coulomb-stabilized clusters involving two Mn$_{Ga}$ and one Mn$_i$. While isolated Mn$_i$ are hole killers (donors), and therefore destroy ferromagnetism,complexes such as Mn$_{Ga}$-Mn$_i$-Mn$_{Ga}$) are found to be more stable than complexes involving Mn$_{Ga}$-Mn$_{Ga}$-Mn$_{Ga}$. The former complexes exhibit partial or total quenching of holes, yet Mn$_i$ in these complexes provide a channel for a ferromagnetic arrangement of the spins on the two Mn$_{Ga}$ within the complex. This suggests that ferromagnetism in Mn doped GaAs arises both from holes due to isolated Mn$_{Ga}$ as well as from strongly Coulomb stabilized Mn$_{Ga}$-Mn$_i$-Mn$_{Ga}$ clusters.