• Journal of Magnetics
• /
• v.11 no.1
• /
• pp.51-54
• /
• 2006

Variation of magnetic properties through Cr substitution for Co in inverse-spinel $CoFe_2O_4$ has been investigated by vibrating-sample magnetometry (VSM) and conversion electron $M\ddot{o}ssbauer$ spectroscopy (CEMS). $Cr_{x}Co_{1-x}Fe_2O_4$ samples were prepared as thin films by a sol-gel method. The lattice constant of the $Cr_{x}Co_{1-x}Fe_2O_4$ samples was found to remain unchanged, explainable in terms of a reduction of tetrahedral $Fe^{3+}$ ion to $Fe^{2+}$ due to substitution of $Cr^{3+}$ ion into octahedral $Co^{2+}$ site. The existence of the tetrahedral $Fe^{2+}$ ions in $Cr_{x}Co_{1-x}Fe_2O_4$ was confirmed by CEMS analysis. Room-temperature magnetic hysteresis curves for the $Cr_{x}Co_{1-x}Fe_2O_4$ films measured by VSM revealed that the saturation magnetization $M_s$ increases by Cr doping. The $M_s$ is maximized when x = 0.1 and decreases for higher x but is still bigger than that of $CoFe_2O_4$. The increase of $M_s$ can be explained partly by the reduction of the tetrahedral $Fe^{3+}$ ion to $Fe^{2+}$.

• Journal of the Korean Magnetics Society
• /
• v.17 no.1
• /
• pp.30-33
• /
• 2007

The $FeIn_2S_4$ exhibits an inverse spinel which Fe ions are occupied to the octahedral(B) site, while In ions are occupied to both the tetrahedral(A) and the octahedral(B) site. The $N\'{e}el$ temperature($T_N$) is determined to be 13 K. The effective moment of $FeIn_2S_4$ found to be $5.094{\mu}_B$ from the fit of Curie-Weiss inverse susceptibility for the temperature range over $T_N$, implying angular momentum contribution. The angular momentum contribution is shown in $M\"{o}ssbauer$ spectra for the antiferromagnetic ordering region($T{\leq}\;13K$), too. A weak $Fe^{2+}(B)-S^2-Fe^{2+}(B)$ interaction is responsible for a low $N\'{e}el$ temperature($T_N$) in $FeIn_2S_4$ system. The temperature dependence of electric quadrupole interaction is explained by z-axial crystalline field energy.

• Journal of the Korean Magnetics Society
• /
• v.21 no.3
• /
• pp.88-92
• /
• 2011

We grew $Zn_{0.4}Fe_{2.6}O_4$ thin films using Pulsed Laser Deposition and studied their crystal structure and magnetical characteristics as a function of growth temperature ($T_g$). For the film with $T_g=300^{\circ}C$, X-ray reflections from ${\alpha}-Fe_2O_3$ and ZnO were observed. However, when $T_g$ was increased from 300 to $500^{\circ}C$, crystal structure of inverse spinel was stabilized with the crystal orientation of $Zn_{0.4}Fe_{2.6}O_4(111)/Al_2O_3(0001)$ without any detection of ${\alpha}-Fe_2O_3$ and ZnO phases. The surface morphology shows flattening behavior with increasing $T_g$ from 300 to $500^{\circ}C$. These observations indicate that Zn is substituted into tetrahedron A-site of the inverse-spinel $Fe_3O_4$. M-H curves exhibit clear ferromagnetism for the sample with $T_g=500^{\circ}C$ whereas no ferromagnetism is observed for the film with $T_g=300^{\circ}C$.

• Journal of the Korean Magnetics Society
• /
• v.17 no.2
• /
• pp.51-54
• /
• 2007

By substituting Cr in inverse-spinel $Fe_3O_4,\;Cr_xFe_{3-x}O_4$ thin film samples were prepared by sol-gel spin-coating method and their structural electronic, and magnetic properties were analyzed. X-ray diffraction indicates that the lattice constant decrease with increasing Cr composition (x). This result can be explained in terms of occupation of octahedral sites by $Cr^{3+}$ ions with smaller ionic radius than that of $Fe^{3+}$ Vibrating sample magnetometry measurements on the samples at room temperature revealed that saturation magnetization ($M_s$) decrease by Cr substitution, explainable by comparing spin magnetic moment among the related transition-metal ions. A decrease of magnetoresistence effect with x was observed, similar to that of $M_s$. The coercivity of the $Cr_xFe_{3-x}O_4$ films was found to increase with x, attributed to the increase of magnetic anisotropy by the existence of octahedral $Cr^{3+}(d^3)$.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.318.2-318.2
• /
• 2016

FeM2X4 spinel structures, where M is a transition metal and X is oxygen or sulfur, are candidate materials for spin filters, one of the key devices in spintronics. Both the Fe and M ions can occupy tetrahedral and octahedral sites; therefore, these types of compounds can display various physical and chemical properties [1]. On the other hand, the electronic and magnetic properties of these spinel structures could be modified via the control of cation distribution [2, 3]. Among the spinel oxides, iron manganese oxide is one of promising materials for applications. FeMn2O4 shows inverse spinel structure above 390 K and ferrimagnetic properties below the temperature [4]. In this work, we report on the structural and magnetic properties of epitaxial FeMn2O4 thin film on MgO(100) substrate. The reflection high energy electron diffraction (RHEED) and X-ray diffraction (XRD) results indicated that films were epitaxially grown on MgO(100) without the impurity phases. The valance states of Fe and Mn in the FeMn2O4 film were carried out using x-ray photoelectron spectrometer (XPS). The magnetic properties were measured by vibrating sample magnetometer (VSM), indicating that the samples are ferromagnetic at room temperature. The structural detail and origin of magnetic ordering in FeMn2O4 will be discussed.

• Journal of Magnetics
• /
• v.19 no.2
• /
• pp.111-115
• /
• 2014

X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM) were used to investigate the influence of Ni ions on the structural, electronic, and magnetic properties of nickel-ferrites ($Ni_xFe_{3-x}O_4$). Spinel $Ni_xFe_{3-x}O_4$ ($x{\leq}0.96$) samples were prepared as polycrystalline thin films on $Al_2O_3$ (0001) substrates, using a sol-gel method. XRD patterns of the nickel-ferrites indicate that as the Ni composition increases (x > 0.3), a structural phase transition takes place from cubic to tetragonal lattice. The XPS results imply that the Ni ions in $Ni_xFe_{3-x}O_4$ substitute for the octahedral sites of the spinel lattice, mostly with the ionic valence of +2. The minority-spin d-electrons of the $Ni^{2+}$ ions are mainly distributed below the Fermi level ($E_F$), at around 3 eV; while those of the $Fe^{2+}$ ions are distributed closer to $E_F$ (~1 eV below $E_F$). The magnetic hysteresis curves of the $Ni_xFe_{3-x}O_4$ films measured by VSM show that as x increases, the saturation magnetization ($M_s$) linearly decreases. The decreasing trend is primarily attributable to the decrease in net spin magnetic moment, by the $Ni^{2+}$ ($2{\mu}_B$) substitution for octahedral $Fe^{2+}$ ($4{\mu}_B$) site.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2007.05a
• /
• pp.52.2-52.2
• /
• 2007

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.7 no.2
• /
• pp.244-252
• /
• 1997

The pseudo-spinel type solid solution, $LiAl_{2.5}/Fe_{2.5}O_8$ was prepared by reaction of $LiCO_3, Al_2O_3, Fe_2O_3$ mixture at 1620K, which can be used for cathode material in lithium batteries. Its structure was investigated by Rietveld profile-analysis of XRD in detail. The space group of solid solution is $P4_3$32(a=8.1293$\AA$) and the final residual index of structure refinement was about 5%. Cations $Al^{3+}, Fe^{3+}$ are located at both tetra- and octahedral-coordination and $Li^+$ ions are occupied in the octahedral 4b-, 12d-site of the inverse spinel.

• Bulletin of the Korean Chemical Society
• /
• v.30 no.6
• /
• pp.1305-1308
• /
• 2009

The experimental particle samples included ($Mn_{0.1}Fe_{0.9}$)O-$Fe_2O_3$ and FeO-($Gd_{0.1}Fe_{0.9}$)$_2O_3$ with $Mn^{2+}\;and\;Gd^{3+}$ substitutions in inverse spinel $Fe_3O_4$. A lecithin surfactant was adsorbed onto the magnetic particles by ultrasonication. The samples prepared showed excellent dispersibility at the mean size of 13 nm; their saturation magnetization values were 63 emu/g for the bare and Mn-substituted magnetites, and 56 emu/g for the Gd-substituted magnetite. The crystal structure of the substituted magnetites was very similar to that of the bare magnetite, due to a small amount of 0.1 mole fraction substituted in synthesizing the magnetite. The magnetite fluids, according to T2-weighted MR images, effectively diminished the signal intensity in the liver and spleen of Sprague-Dawley rats.

• Journal of the Korean Magnetic Resonance Society
• /
• v.22 no.4
• /
• pp.101-106
• /
• 2018

Magnetite is the oldest magnet material known to mankind. It is getting attention again from solid state physics researchers now a days because it is one of the most strongly correlated electron systems. Spin, charge, and orbital orders are interplaying with lattice and involved in the Verwey transition where magnetization, conductivity, and structure changes suddenly. The peculiar ordering states above and below the transition temperature mainly originate from the coexistence of $Fe^{2+}$ and $Fe^{3+}$ ions in the B site of the inverse spinel structure. In particular, the state of the charge and orbital order was the oldest and most intriguing problem. NMR has made significant contribution to the investigation of this question. A. Abragam stated that there is no doubt that NMR is a very powerful tool for the study of ferromagnetic and antiferromagnetic materials. In this mini-review, a short history of NMR investigation of magnetite is presented, providing a support to Abragam's claim.