Coexistence Of Weak Ferromagnetism Research Articles

Observation of Exchange Bias in Antiferromagnetic Cr0.79Se Due to the Coexistence of Itinerant Weak Ferromagnetism at Low Temperatures.

We report on the structural, electrical transport, and magnetic properties of antiferromagnetic transition-metal monochalcogenide Cr0.79Se. Different from the existing off-stoichiometric compositions, Cr0.79Se is found to be synthesized into the same NiAs-type hexagonal crystal structure as that of CrSe. Resistivity data suggest Cr0.79Se to be a Fermi-liquid-type metal at low temperatures, while at intermediate temperatures, the resistivity depends sublinearly on the temperature. Eventually, at elevated temperatures, the rate of change of resistivity rapidly decreases with increasing temperature. Magnetic measurements suggest a transition from the paramagnetic phase to an antiferromagnetic phase at a Néel temperature of 225 K. Further reduction of the sample temperature results in the coexistence of weak ferromagnetism along with the antiferromagnetic phase below 100 K. As a result, below 100 K, we identify a significant exchange bias due to the interaction between the ferro- and antiferromagnetic phases. In addition, from temperature-dependent X-ray diffraction measurements, we observe that the NiAs-type structure is stable up to as high as 600 °C.

Effect of Transition Metal Ion Doping on the Microstructure, Defect Evolution, and Magnetic and Magnetocaloric Properties of CuFeO2 Ceramics

The polycrystalline CuFeO2 (CFO) and CuFe1-xMxO2 (M = Ti, Hf, Zr, M-CFO) samples are synthesized by solid-state reaction method. The doping effect of tetravalent nonmagnetic transition metal M4+ ions on the microstructure, defect evolution, and magnetic and magnetocaloric properties of the CFO system are comparatively investigated. The substitution of M4+ for Fe3+ increases lattice parameters, changes the bond length of Fe/Cu-O and bond angle of Fe-O-Fe, and improves the microstructure to some extent. Positron annihilation spectroscopy results indicate that M4+ doping induces the agglomeration of small-sized vacancy defects manifested as the increase in vacancy-type defect size and the suppression of inherent defect concentration. Magnetic measurements show that the antiferromagnetic stability of CFO system is clearly affected by M4+ doping, and Ti4+ doping has a more noticeable impact than Hf4+ and Zr4+ doping. Meanwhile, the coexistence of weak ferromagnetism and antiferromagnetism is detected in all doped samples, while Ti-doped system exhibits extraordinary magnetic properties. Especially for Ti-CFO2 (x = 0.03) sample, the maximum magnetization reaches as high as 11.81 emu/g at 0.5 T, which enhanced one order of magnitude than that of undoped CFO. Isothermal M-H data at different temperatures show that entropy change (ΔSM) and refrigerant capacity (RC) for CFO and M-CFO2 samples are significantly weakening with M4+ substitution in bulk CFO. The maximum ΔSM = 4.79 J·kg−1 K−1 and RC = 12.79 J·kg−1 for undoped CFO are obtained near the transition temperature TN2 = 12 K, with the applied fields up to 6 T. The possible reasons for the above observations are discussed in detail.

Investigations of Ti-substituted CuFeO2 ceramics on the structure, defects, the local electron density and magnetic properties

Abstract CuFe1−xTixO2 (0 ≤ x ≤ 0.08) ceramics are synthesized by solid state reaction method to investigate the effect of Ti substitution on the microstructure, vacancy-type defects, the local electron density, and magnetic properties. The XRD and Raman spectra results show that all experimental samples possess the characteristic peak of CuFeO2 ceramics. SEM observations indicate that Ti substitution has obvious influence on the morphologies of experimental ceramics, and the microvoids increases significantly with increasing Ti content. Positron annihilation lifetime and Doppler broadening spectra results indicate that the vacancy concentration increases rapidly and then reaches a higher platform (>35%) as x > 0.01, and Ti substitution does not change the defects species in CuFe1-xTixO2 ceramics. The electron density decreases with increasing x and then reaches a low plateau (≈5.7) at x = 0.08. The χ - T curves reveal that the TN1 is independent of Ti content, while, the TN2 decreases with increasing x at x = 0.00–0.02 and even disappears in the magnetization curves as x > 0.02. The M-H curves indicate that the coexistence of weak ferromagnetism and antiferromagnetism for all the samples could be found. The possible reasons for the above observations are discussed in detail.

Electrical and magnetic properties of Aurivillius phase Bi5Fe1-xNixTi3O15 thin films prepared by chemical solution deposition

The Aurivillius Bi5Fe1-xNixTi3O15 (BFNT-x) (0≤x≤0.5) thin films were deposited by chemical solution deposition route. The microstructures, electrical and magnetic properties were systematically investigated in BFNT films. It has been found that the c-orientation of the films increases with the increase of Ni content. The coexistence of weak ferromagnetism and ferroelectricity at room temperature were observed in BFNT films except the x = 0.5 sample. The BFNT-0.1 sample exhibits a maximum remnant polarization 2Pr ∼49.3 μC/cm2, which is enhanced by 12.6% compared with that of the Ni-free thin film. The leakage current is decreased evidently with Ni content less than 0.3. The BFNT-0.1 film also shows the highest remnant magnetization 2Mr ∼2.14 emu/cm3. The origins of weak ferromagnetism in the BFNT films are attributed to the spin canting of the antiferromagnetic (AFM) coupling caused by Dzyaloshinskii-Moriya (DM) interaction based the Fe-O and Ni-O octahedral and affected by other causes as discussed. The saturation magnetization values of in-plane loops are smaller than that of the out-of-plane loops, indicating obvious anisotropic magnetism. These results demonstrate that partial substitution of Ni for Fe is an effective way for improving the multiferroic properties of Aurivillius compounds.

Coexistence of weak ferromagnetism with magnetoelectric coupling in Fe substituted Co4Nb2O9

Co4Nb2O9 (CNO) having Co chains along c-direction shows gigantic magnetoelelctric coupling below antiferromagnetic ordering temperature of 27.3 K but above a spin flop field of 1.6 T. We have investigated the effect of substitution of 20% of isovalent magnetic Fe2+ on magnetic and magnetoelectric properties. With Fe substitution, magnetization with temperature has shown a weak ferromagnetic behavior at low magnetic fields and antiferromagnetic like behavior at higher fields. Interestingly, linear magnetoelelctric and ferroelectric behaviors are evidenced in the Fe substituted samples but for an electric field as small as 5 kV/m and the magnetoelelctric coupling is ensured for magnetic fields as low as 0.25 T, which is far below the spin flop field. The reduction in single ion anisotropy of Co and modified Dzyaloshinkii-Moriya interactions with Fe appear to be important in inducing low field ME effect.

A series of anionic host coordination polymers based on azoxybenzene carboxylate: structures, luminescence and magnetic properties.

A series of coordination polymers {[Ln(aobtc)(H2O)4]·Hbipy·H2O}n (H4aobtc = azoxybenzene-2,2',3,3'-tetracarboxylic acid, bipy = 4,4'-bipyridine, and Ln = Sm(1), Eu(2), Gd(3), Tb(4), Dy(5), Er(6)) have been synthesized and characterized systematically. The cationic Hbipy+ guest incorporated polymers are isostructural sets, featuring a one-dimensional (1D) zigzag double chain edifice composed of binuclear clusters [Ln2(H4aobtc)2], with the Hbipy+ guest being located on two sides. These 1D chains are further interlinked into a 2D layer structure, and further extended into a 3D framework through hydrogen bonding interactions. The luminescence emission spectra of polymers 2 and 3 are based on the H4aobtc acid ligands, while 1 and 4 display the characteristic f-f transitions of Ln(iii) ions. Magnetic measurements revealed the presence of ferromagnetic behavior in polymer 3. The magnetic behaviors of 4 and 6 are ascribed to the depopulation of the Stark levels and/or weak antiferromagnetic interactions within MOFs at lower temperature. Slow relaxation is observed through the alternating-current susceptibility measurements for 5 at lower temperature, and the coexistence of weak ferromagnetism corresponding to the spin-canting-like behavior.

Coexistence of weak ferromagnetism and polar lattice distortion in epitaxial NiTiO3 thin films of the LiNbO3-type structure

The authors report the magnetic and structural characteristics of epitaxial NiTiO3 films grown by pulsed laser deposition that are isostructural with acentric LiNbO3 (space group R3c). Optical second harmonic generation and magnetometry demonstrate lattice polarization at room temperature and weak ferromagnetism below 250 K, respectively. These results appear to be consistent with earlier predictions from first-principles calculations of the coexistence of ferroelectricity and weak ferromagnetism in a series of transition metal titanates crystallizing in the LiNbO3 structure. This acentric form of NiTiO3 is believed to be one of the rare examples of ferroelectrics exhibiting weak ferromagnetism generated by a Dzyaloshinskii–Moriya interaction.

Orientation dependence of proximity effect in ferromagnet/$\mathsf{d}$-wave superconductor junctions

The Nambu spinor Green’s function approach is applied to studying the proximity effect in ferromagnet/d-wave superconductor (FM/d-wave SC) junctions. It is found that the magnitude of the proximity effect depends to a great extent on the orientation of the SC crystal with respect to the interface normal. On the FM side, near the interface there are two different types of density of states (DOS) with superconducting features. On the SC side, the DOS near the interface is spin dependent, indicating a local coexistence of weak ferromagnetism and d-wave superconductivity.

Weak ferromagnetic ordering in the superconducting state of ErNi 211B 2C

Recently a possible coexistence of weak ferromagnetism and superconductivity was proposed for ErNi 2B 2C. We have performed unpolarized neutron diffraction experiments on a large single crystal, and demonstrate that such an exotic phase is realized in this system below T WF=2.5 K. However, the virgin magnetization curve shows diamagnetic behavior even below T WF, indicating that there is no spontaneous vortex phase in a ZFC process. In addition, we also discuss future prospects of our project based on the results presented in this paper.