Li-gang Zhang

Bio: Li-gang Zhang is an academic researcher from Wuhan University of Science and Technology. The author has contributed to research in topics: Magnetization & Antiferromagnetism. The author has an hindex of 8, co-authored 25 publications receiving 150 citations.

Large coercivity in nanocrystalline TbMn6Sn6 permanent magnets prepared by mechanical milling

Abstract: Isotropic TbMn6Sn6 was prepared by mechanical milling and subsequent annealing. Although the crystalline grain size was a little larger than 15 nm, no remanence enhancement resulting from intergrain exchange coupling was observed. The coercivity μ0Hc = 0.96 T at 293 K was much larger than that expected from magnetocrystalline anisotropy. The smallest effective anisotropy constant is suggested to be 0.25 MJ m−3 when the coercivity mechanism is controlled by coherent rotation of magnetization in a single-domain grain. The contributions of shape anisotropy and magnetoelastic anisotropy are considered in order to explain the large coercivity in the magnets.

Magnetic phase in LaFe11.4Al1.6 with very low interstitial carbon content

Abstract: NaZn13-type LaFe11.4Al1.6C delta (delta=0-0.08) compounds were prepared by arc melting. At low temperature, the ground state is antiferromagnetic and ferromagnetic for delta=0 and 0.04, respectively. Although the ground state remains antiferromagnetic for delta=0.02, the ferromagnetic state can be induced by a magnetic field at about 100 K. During the transition between antiferromagnetic and ferromagnetic states, the magnetization exhibits a sharp discontinuity, indicating the formation of a homogeneous phase by intersitial carbon in spite of the very small delta. The transition from low-temperature antiferromagnetic state (AFI) to ferromagnetic state induced by a magnetic field is irreversible. On the contrary, the transition from high-temperature antiferromagnetic state (AFII) to ferromagnetic state is reversible. Considering the magnetization behaviors and the variation of heat capacity with temperature, we can deduce that the AFI is different from the AFII.

Multiple magnetic transitions and large magnetoresistance of the Y0.5Ho0.5Mn6Sn6 compound

Abstract: Magnetic transitions and magnetoresistance of the HfFe6Ge6-type Y05Ho05Mn6Sn6 compound have been investigated in the temperature range of 5–380 K It was found that the compound displays paramagnetism, ferrimagnetism, antiferromagnetism, and reentrant ferrimagnetism with decreasing temperature The temperature range of the antiferromagnetic state can be narrowed by increasing the magnetic field, and the metamagnetic transition from the antiferro- to ferrimagnetic state can be induced by a fairly small threshold field (<6 kOe) The antiferro-ferrimagnetic transition is accompanied by a large magnetoresistance effect of about −16% at 100 K The magnetic transitions with temperature and magnetic field are both of the second order

Structure and magnetic properties of ( x = 0-3) compounds with R = Y and Pr

Abstract: The influence of Si substitution for Co on the structure and magnetic properties of and (x = 0-3) compounds were investigated by means of x-ray diffraction and magnetization measurements. X-ray diffraction patterns demonstrate that all samples are single phase with the hexagonal -type structure for and the rhombohedral -type structure for compounds, except for with a small amount of impurity phases. The unit-cell volume is found to decrease linearly with increasing Si concentration in both series. The Curie temperature decreases monotonically with increasing Si concentration at an approximate rate of 205 and 175 K per Si atom for the and compounds, respectively. The saturation magnetic moments of (R = Y, Pr) decrease with increasing Si content and the decline rates are larger than that expected as a simple dilution. For , the substitution of Si has a significant effect on the magnetocrystalline anisotropy of the Co sublattice, and changes the easy magnetization direction from the basal plane to the c-axis at room temperature. For , the Si substitution has not changed the easy magnetization direction at room temperature. However, the spin-reorientation transitions from the basal plane to the c-axis for this series with were observed above room temperature with increasing temperature. The spin-reorientation temperature first decreases with increasing Si content and then increases at higher x values (x > 2). The origin of this spin reorientation is interpreted by the competition between the Pr sublattice anisotropy and the Co sublattice anisotropy. This has been confirmed by the magnetocrystalline anisotropy measurements on .

Unusual magnetic and transport properties of layered compound ErMn6Sn6

Abstract: The magnetic and magnetotransport properties of the polycrystalline ErMn6Sn6 compound have been investigated in the temperature interval of 5–380 K. The compound shows paramagetism, antiferromagnetism, and ferrimagnetism with decreasing temperature. In the antiferromagnetic state (67–362 K), the transition from antiferromagnetism to ferrimagnetism can be induced by an applied field, and the metamagnetic transition field increases from 0.2 kOe at 80 K to 15 kOe around 200 K and then decreases monotonously to 5 kOe at 330 K. The large magnetoresistance {MR=[R(H)−R(0)]×100%/R(0)} effect is observed with the metamagnetic behavior, such as −9.8% at 135 K under a field of 50 kOe. It is worth noting that ErMn6Sn6 displays the positive MR in the ferrimagnetic state and the negative one in the antiferromagnetic state, respectively, and the origin of the MR anomalies has been discussed.

Enhanced magnetic and dielectric properties of Eu and Co co-doped BiFeO3 nanoparticles

Abstract: Bi1−xEuxFe1−yCoyO3 (x = 0, 0.01; y = 0, 0.01) nanoparticles, having an average size of 13 nm, were prepared by a simple sol gel route. Strong electronegativity of Eu3+ and smaller oxidation-reduction potential of Co3+/Co2+ (0.55 eV) than Fe3+/Fe2+ (1.3 eV) increase the concentration of Fe3+ ions with doping. Distinct magnetic hysteresis and complete saturation of magnetisation indicate the presence of ferromagnetic phase. The successful co-doping of Eu and Co into BiFeO3 (BFO) lattice dramatically enhances the saturation magnetization (Ms) and coercivity (Hc) by about 20 times than that of pure BiFeO3. A large value of dielectric constant of about 650, low loss (<0.001), and small leakage current density (1.79 × 10−8 A/cm2) are observed for the co-doped sample.

Magnetic and dielectric properties of Eu-doped BiFeO3 nanoparticles by acetic acid-assisted sol-gel method

Abstract: The BiFeO3 nanoparticles, having an average size of 13 nm, were synthesized by a simple sol-gel method. The samples possess single phase up to 2% Eu doping at the Bi site. The uncompensated spin moments on the surface and the modification of cycloidal spin structure due to the small size (13 nm) result in a ferromagnetic phase of the BiFeO3 nanoparticles. The successful doping of magnetically active Eu3+ ions in BiFeO3 nanoparticles improves the ferromagnetic property. The similar dependency of saturation magnetization, coercive field, and dielectric constant on Eu doping concentration reveals that a correlation between magnetic and dielectric properties exists in Eu-doped BiFeO3 nanoparticles.

Effect of In and Mn co-doping on structural, magnetic and dielectric properties of BiFeO 3 nanoparticles

Abstract: Bi1−xInxFe1−yMnyO3 (x = 0, y = 0; x = 0.1 y = 0; x = 0, y = 0.1; x = 0.05, y = 0.05) nanoparticles were prepared by a simple cost effective ethylene glycol based solution combustion route. The XRD analysis reveals the single phase rhombohedral structure for BiFeO3 (BFO) and In and Mn co-doped BFO (BIFMO) samples. Some structural distortion is observed for the In and Mn co-doped samples. The co-doping of In and Mn at A-B-site of BFO improves the particles’ surface morphology and reduces the average grain size to around 15nm which evidently affects the magnetic and electrical properties of these nanoparticles. The saturation magnetization enhances significantly from 0.20emug −1 for BFO to 3.50emug −1 for the co-doped sample. The enhanced saturation magnetization is attributed to the size effect. The co-doping decreases the coercivity to around 32Oe due to a decrease in the magneticrystalline anisotropy. The co-doping improves the dielectric constant and dielectric loss and results in the modification of dielectric behaviour with varying temperatures up to 250 ◦ C. All doped samples show high resistivity of the order of 10 9 � cm which further improves with co-substitution of In and Mn and is attributed to the presence of small grain size and reduction of oxygen ion vacancies. (Some figures may appear in colour only in the online journal)

Influence of cobalt doping on structural and magnetic properties of BiFeO 3 nanoparticles

Abstract: Nanocrystalline cobalt-doped bismuth ferrites with general formula of BiFe1−δ Co δ O3 (0 ≤ δ ≤ 0.1) have been synthesized using solution evaporation method. Structure and phase identification was performed with X-ray diffraction (XRD) technique. The results confirm the formation of rhombohedral-distorted Perovskite structure with R3c symmetry. A decrease in lattice parameters and an increase in X-ray density have been observed with increasing cobalt concentration in BiFeO3. Particle size determined by transmission electron microscope was in good agreement with XRD, i.e., 39 nm. Room-temperature coercivity and saturation magnetization of nanoparticles were increased up to 7.5 % of cobalt doping. Low-temperature magnetic measurements of selected sample showed increasing behavior in saturation magnetization, coercivity, effective magnetic moments, and anisotropy constant. An increase in coercivity with decrease in temperature followed theoretical model of Kneller’s law, while modified Bloch’s model was employed for saturation magnetization in temperature range of 5–300 K.