Chin Mo Kim

Investigation of magnetic properties of non-magnetic ion (Al, Ga, In) doped Ba2Mg0.5Co1.5Fe12O22

Ba2Mg0.5Co1.5Fe12O22 (non-doped) and non-magnetic ion (Al, Ga, In) doped Ba2Mg0.5Co1.5(Fe0.99M0.01)12O22 (M-doped) polycrystalline samples were prepared by the solid-state reaction method. The crystal structures and magnetic properties of samples were investigated with x-ray diffractometer (XRD), vibrating sample magnetometer (VSM), and Mossbauer spectroscopy. The crystal structures of non-doped and M-doped samples were determined as hexagonal structures with R-3m space group by the Rietveld refinement. The unit cell volume (Vu) of non-doped sample was Vu = 1298.0 A3, while those of M-doped samples (M = Al, Ga, In) were Vu = 1295.7, 1296.7, and 1299.9 A3, respectively. From the magnetic hysteresis curves at room temperature, the saturation magnetization (Ms) and coercivity (Hc) of non-doped sample were found to be Ms = 28.0 emu/g and Hc = 255.4 Oe, but those of M-doped samples (M = Al, Ga, In) were Ms = 24.7, 28.4, 28.6 emu/g, and Hc = 222.0, 215.9, 190.7 Oe, respectively. From the temperature dependence ...

Site Preference for Fe in Zn-Doped Y-Type Barium Hexaferrite

Polycrystalline Ba₂Zn_xCo_2-xFe₁₂O₂₂ samples were prepared by solid state reaction method. The crystallographic structure and magnetic properties of the Zn-doped Y-type hexaferrite samples were investigated by X-ray diffraction, magnetization, and Mössbauer spectroscopy measurements. The crystal structure was found to be hexagonal with space group of <i>R</i>-3/<i>m</i>. The lattice constants of the samples increased as Zn contents increase. From the temperature dependence of magnetization, measured from 50 to 700 K, the magnetic transition temperature (<i>T</i>_S,<i>T</i>_C) of Ba₂Zn_xCo_2-xFe₁₂O₂₂ decreased with increasing Zn concentration. Mössbauer spectra of Ba₂Zn_xCo_2-xFe₁₂O₂₂(x=0,1) were obtained at various temperature ranging from 4.2 to 300 K. Based on the observed spectra, the site occupancies in six interstitial sites of Co, Zn and Fe ions were calculated from the average of the relative sub-spectra absorption areas. Increasing Zn contents, the Debye temperature of the samples decreased. The isomer shift values of the samples at various temperatures were 0.1 <; δ <; 0.45mm/s, relative to the Fe metal, which were consistent with the Fe³⁺ valance state.

Structural and magnetic phase transition of mixed olivines LixFe1−yNiyPO4 by lithium deintercalation

The structural and magnetic phase transitions of LixFe1–yNiyPO4 were investigated by x-ray diffraction (XRD), superconducting quantum interference device magnetometry, and Mossbauer spectroscopy. Rietveld refinement of XRD patterns of LiFe1–yNiyPO4 (0.0 ≤ y ≤ 0.6) revealed that the lattice parameters a0 = 10.328, b0 = 6.007, and c0 = 4.692 A for LiFePO4 changed linearly to a0 = 10.154, b0 = 5.923, and c0 = 4.687 A for LiFe0.4Ni0.6PO4 with the substitution of Ni ions. Also, the fully lithium-deintercalated Fe1–yNiyPO4 (0.0 ≤ y ≤ 0.6) series had enhanced lattice distortions along the c axis compared to LiFe1-yNiyPO4 because the Jahn–Teller distortion changed as the unit cell volume decreased due to lithium ion deintercalation. LiFe1–yNiyPO4 has an antiferromagnetic order; the magnetic Neel temperature (TN) decreased from 51 K for LiFePO4 to 36 K for LiFe0.4Ni0.6PO4. Fully deintercalated Fe1–yNiyPO4 has strong antiferromagnetic order; TN decreased from 114 K for FePO4 to 62 K for Fe0.4Ni0.6PO4 due to the cha...

Investigation of electrical and magnetic properties of triangular antiferromagnets

We have synthesized magnetic Fe-doped NiGa2S4 and investigated its electrical and magnetic properties with a superconducting quantum-interference device magnetometer, Mossbauer spectroscopy, and a physical property measurement system. X-ray diffraction analysis at room temperature shows that the prepared samples are single phase with trigonal structure (P-3m1). From zero-field-cooled (ZFC) and field-cooled magnetization curves under 100 Oe between 4.2 and 200 K, we have measured the temperature-dependent susceptibility χ of Ni1−xFexGa2S4. A cusp is observed in the ZFC measurement for the samples with x ≥ 0.1, which is due to the spin-freezing effect in the spin-glass system. Moreover, with increasing Fe concentration, the sample shows the antiferromagnetic behavior and the increase in freezing temperature Tf. This, in turn, suggests that the spin-averaged value of the sample increases and antiferromagnetic spin–spin interaction becomes stronger with Fe concentration. The temperature-dependent resistance o...

Mössbauer Study of the Dynamics in BaFe 12 O 19 Single Crystals

Mossbauer spectra of hexagonal BaFe12O19 single crystals were studied at various temperatures (4-300 K). It was found that the spin states in Fe atoms were parallel to the γ-rays direction into a single crystal along the caxis. The location of the Fe ion in the 2b site is unusual in an oxide structure and has strong anisotropic lattice vibrations. Moreover, at room temperature, the zero absorption lines of the Fe ions at the 2b site were observed due to fast diffusion motion in a double well atomic potential. The two Fe ions of the single crystal mainly enter into the sites in the mirror plane of the trigonalbipyramidal structure.

Magnetic properties of the ferrimagnetic FeCr2−xMxS4 (M=In,Al)

The polycrystalline samples of ferrimagnetic FeCr2−xMxS4 (M=In,Al; x=0.1,0.3) have been studied with x-ray diffraction, magnetization, and Mossbauer spectroscopy measurements. The crystal structure was found to be cubic spinel with Fd-3m space group. The lattice constants (a0) of the samples were linearly increased with Al and In concentration. Mossbauer spectra of FeCr2−xMxS4 (M=In,Al; x=0.1,0.3) were obtained at various temperatures ranging from 4.2 to 300 K. Magnetic hyperfine field and electric quadrupole interactions for FeCr2−xMxS4 (M=In,Al; x=0.1) at 4.2 K have been fitted, yielding the following results: for M=Al, Hhf=139 kOe, ΔEQ=2.54 mm/s, θ=30°, φ=0.0°, η=0.9, and R=2.7; and for M=In, Hhf=126 kOe, ΔEQ=2.64 mm/s, θ=30°, φ=0.0°, η=1.0, and R=3.1. The isomer shift (δ) value of the FeCr2−xMxS4 (x=0.1) samples for both M=Al and In at 300 K was 0.50 mm/s, relative to the Fe metal, which is consistent with the Fe2+ valence state. The Debye temperatures (ΘD) of the FeCr2−xAlxS4 (x=0.1,0.3) sample were ...

A Study on the Magnetic Properties of Al-Doped Sulphur Spinel

FeCr_2-xAl_xS₄ ( x=0.1, 0.3, and 0.5) samples were prepared by solid state reaction method. The crystallographic structure and magnetic properties of the fabricated compounds were investigated by X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometer, and Mo¿ssbauer spectroscopy. The crystal structure is determined to be a cubic spinel with the space group of Fd-3m and the lattice constants <i>a</i> ₀= 9.998, 10.004, and 10.010 A¿ , respectively. The temperature dependence of magnetization, measured from 5 to 300 K, suggests that FeCr_2-xAl_xS₄ (x=0.1, 0.3, and 0.5) samples show ferrimagnetic behavior. The decrease of Ne¿el temperature compared with FeCr₂S₄ could be interpreted by weakening of the exchange interaction by substitution of nonmagnetic Al ions. Mo¿ssbauer spectra of FeCr_2-xAl_xS₄ ( x= 0.1, 0.3, and 0.5) were obtained at various temperatures ranging from 4.2 to 300 K. Isomer shift values of the samples at various temperatures for FeCr_2-xAl_xS₄ (x=0.1 , 0.3, and 0.5) were 0.50 ¿ ¿ ¿ 0.73 mm/s, relative to the Fe metal, which are consistent with the Fe²⁺ valence state.