• Journal of the Korean Magnetics Society
• /
• v.6 no.6
• /
• pp.361-366
• /
• 1996

$NdFe_{10.7}Ti_{1.3}$ has been studied with X-ray diffraction, Mossbauer spectroscopy and vibrating sample magnet-ometer(VSM). The alloys were prepared by arc-melting under an argon atmosphere. The $NdFe_{10.7}Ti_{1.3}$ contains some $\alpha-Fe$, from X-ray and Mossbauer measurements. The $NdFe_{10.7}Ti_{1.3}$ has the $ThMn_{12}$-type tetragonal struc-ture with $a_{0}=8.607{\AA}\;and\;c_{0}=4.790{\AA}$. The Curie temperature ($T_c$) of the $NdFe_{10.7}Ti_{1.3}$ is 590 K from $M\"{o}ssbauer$ spectroscopy performed at various temperatures ranging from 13 to 800 K. Each spectrum below $T_c$ was fitted with six subspectra of Fe sites in the structure$(8i_{1},\;8i_{2},\;8j_{2},\;8j_{1},\;8f\;and\;{\alpha}-Fe)$. The area fractions of the subspectra at room temperature are 13.8%, 15.4%, 17%, 16.4%, 34.1% and 3.3%, respectively. Magenetic hyperfine fields for the Fe sites decrease in the order, $H_{hf}(8i)>H_{hf}(8j)>H_{hf}(8f)$. The abrupt changes in the magnetic hyperfine field, isomer shift and magnetic moment observed at about 180 K in $NdFe_{10.7}Ti_{1.3}$ are attributed to spin reorientation.

• Journal of the Korean Magnetics Society
• /
• v.19 no.3
• /
• pp.106-112
• /
• 2009

$Ni_{1-x}Mg_xFe_2O_4$ ferrite system was studied by using X-ray diffraction and $M{\ddot{o}}ssbauer$ spectroscopy. The samples were prepared by ceramic sintering method with Mg content x. The X-ray diffraction patterns of samples show phase of cubic spinel structure. There are no remarkable changes of lattice constants in $Ni_{1-x}Mg_xFe_2O_4$ ferrite system. The $M{\ddot{o}}ssbauer$ spectra were consisted of two sets of six lines, respectively, corresponding to $Fe^{3+}$ at tetrahedral and octahedral sites. The magnetic hyperfine field of samples was decreased as increasing Mg contents x in both sites and it was shown Yafet-Kittel magnetic structure. $NiFe_2O_4$ was shown complete inverse spinel, but $NiFe_2O_4$ was shown partial inverse spinel which absorption area ratio (oct/tet) was 1.449 in $M{\ddot{o}}ssbauer$ spectrum.

• Journal of the Korean Magnetics Society
• /
• v.9 no.3
• /
• pp.136-142
• /
• 1999

$Ni_{0.65}Zn_{0.35}Cu_{0.3}Fe_{1.7}O_4$ has been studied with x-ray diffraction, Mossbauer spectroscopy, and vibrating sample magnetometer. The crystal structure is found to be a cubic spinel with the lattice constant $a_0=8.403{\AA}$. Mossbauer spectra of have been taken at various temperatures ranging from 12 K to 665 K. as the temperature increases toward $T_N$ a systematic line broadening effect in the Mossbauer spectrum is observed and interpreted to originate from different temperature dependencies of the magenetic hyperfine fields at various iron sites. Also, by using binomial distribution equation we obtained the hyperfine fields of tetrahedral[A] and octahedral sites[B], $H_{hf}(A)=470\;kOe,\; H_{hf}(B0)=495 \;kOe,\; H_{hf}(B1)=485\;kOe, \;H_{hf}(B2)=453\;kOe,\; H_{hf}(B3)=424\;kOe,\; H_{hf}(B4)=390\;kOe,\; H_{hf}(Bavr)=451\;kOe$ respectively at room temperature. The isomer shift indicates that the iron ions are ferric at tetrahedral[A] and octahedral sites[B], respectively. The Neel temperature is determined to be $T_N=665\;K$. The results of the VSM data gave the magnetic moment and coercivity values of $M_S=66\; emu/g\;and\;H_C=36\;Oe$.

• Journal of the Korean Magnetics Society
• /
• v.5 no.5
• /
• pp.864-873
• /
• 1995

Amorphous $Fe_{73.5}Cu_{1}Nb_{3}Si_{16.5}B_{6}$ ribbons were annealed for different time at $500^{\circ}C$ and $552^{\circ}C$, just before and after the exothermic reaction in DSC curve. The development of nanocrystalline phase was investigated by means of $M\"{o}ssbsuer$ spectroscopy. The crystalline phase consists mainly of $DO_{3}Fe-Si$. Though slight in amount (5%), another ferromagnetic phase which could be presumed $t-Fe_{3}B$ was detected Si content of $DO_{3}Fe-Si$, Si/(Fe+Si), was 0.218 under the heat treatment at $500^{\circ}C$ for 60 min and 0.222 at $552^{\circ}C$ for 10 min. Since then both of those values decreased with time until 120 min and finally these two values remained constant at 0.210. The variation in Si content with annealing time results in the variation in the hyperfine field and the isomer shift. The increase in the mean hyperfine fields and the decrease in the mean isomer shifts of Fe-Si are caused by the increase in Si content. The volume fractions of residual amorphous phase rapidly decrease during the early stage of annealing and come nearer to saturation after 120 min both at $500^{\circ}C$ and $552^{\circ}C$. The decrease in the mean hyperfine field of residual amorphous. in spite of slight changes in the volume fractions of Fe-Si and of residual amorphous after 120 min. is caused by the increase in the content of Nb and B in residual amorphous phase. The saturated volume fraction of the crystalline phase was 81% for $500^{\circ}C$ (180 min) and 77% for $552^{\circ}C$ (960 min), different from expectation.

• Korean Journal of Materials Research
• /
• v.21 no.8
• /
• pp.439-443
• /
• 2011

The crystal structure and magnetic properties of a new solid solution type ferrite $(Fe_2O_3)_5-(Al_2O_3)_{3.4}-(Ga_2O_3)_{0.6}-SiO$ were investigated using X-ray diffraction and M$\"{o}$ssbauer spectroscopy. The results of the X-ray diffraction pattern indicated that the crystal structure of the sample appears to be a cubic spinel type structure. The lattice constant (a = 8.317 ${\AA}$) decreases slightly with the substitution of $Ga_2O_3$ even though the ionic radii of the Ga ions are larger than that of the Al ions. The results can be attributed to a higher degree of covalency in the Ga-O bonds than in the Al-O and Fe-O bonds, which can also be explained using the observed M$\"{o}$ssbauer parameters, which are the magnetic hyperfine field, isomer shift, and quadrupole splitting. The drastic change in the magnetic structure according to the Ga ion substitution in the $ (Fe_2O_3)_5(Al_2O_3)_{4-x}(Ga_2O_3)_xSiO$ system and the low temperature variation have been studied through a M$\"{o}$ssbauer spectroscopy. The M$\"{o}$ssbauer spectrum at room temperature shows the superpositions of two Zeeman patterns and a strong doublet. It shows significant departures from the prototypical ferrite and is comparable with the diluted ferrite. The doublet of spectrum at room temperature appears to originate from superparamagnetic clusters and also the asymmetry of the doublet appears to be caused by the preferred orientation of the crystallites. The M$\"{o}$ssbauer spectra below room temperature show various complicated patterns, which can be explained by the freezing of the superparamagnetic clusters. On cooling, the magnetic states of the sample were various and multi critical.

• Journal of the Korean Magnetics Society
• /
• v.10 no.1
• /
• pp.16-21
• /
• 2000

Magnetic properties and crystallographic properties of $Cu_{0.95}Ge_{0.95}Fe_{0.1}O_3$ were studied by using x-ray diffraction, superconducting quantum interference device (SQUID) and Mossbauer spectroscopy. Our sample has orthorhombic structure and the lattice constants are a = 4.795 $\AA$, b = 8.472 $\AA$, c = 2.932 $\AA$. The spin-Peierls (SP) transition temperatures of our sample is 13 K. The Mossbauer spectra consisted with two Zeeman sextets and one doublet due to $Fe^{3+}$ions. The Zeeman sextets come from tetrahedral $Fe^{3+}$ions and the doublets come from octahedral $Fe^{3+}$ions. The jump up of magnetic hyperfine field of 2nd Zeeman sextet and the increasing of the values of quadrupole splitting and isomer shift of doublet below SP transition temperature could be interpreted related with the atomic displacements. The N el temperature is 715 K, the Debye temperature are 540 K for octahedral site and 380 K for tetrahedral site, respectively.

• Journal of Magnetics
• /
• v.10 no.1
• /
• pp.14-22
• /
• 2005

Precisely refined Mossbauer study and nano structure observation revealed that intergranular phase formed between a-Fe and Nd₂Fe₁₄B phase in NdFeNbB alloys plays a significant role on the magnetic properties. The intergranular interaction was characterized in term of Henkel Plot (δM plot), and hyperfine field, quardrupole splitting and isomer shift were refined to predict the presence and role of the intergranular phase. By the addition of Nb into Nd₈Fe₈₆B₆ composition, coercivity was found to increase by 25% due to the refinement of average grain size of both the soft and hard magnetic phases which was decreased from 50 nm of virgin Nd/sub 8/Fe/sub 86/B/sub 6/ to 25 nm in Nd₈Fe ₈₅Nb₁B₆ alloys. The role of Nb addition was confirmed to stabilize the Nd₂Fe₁₄B lattice preventing from thermal vibration of the corresponding sites substituted Fe by Nb atoms in all sites in the Nd₂Fe₁₄B lattice. The enhanced coercivity was originated from the exchange hardening of soft and amorphous phases surrounding the hard magnetic Nd₂Fe₁₄B crystal.

• Journal of the Korean Magnetics Society
• /
• v.9 no.3
• /
• pp.143-148
• /
• 1999

Magnetic properties and crystallographic properties of $Cu_{1-x}Ge_{1-y}Fe_{x+y}O_3$ system were studied by using x-ray diffraction, superconducting quantum interference device (SQUID) and Mossbauer spectroscopy. All the samples have orthorhombic structure and the lattice constants some decreased as the substituted iron contents increasing. The spin-Peierls (SP) transition temperature of our samples are about 12.5 K and these temperatures lowered as increasing substituted iron contents. The Mossbauer spectra consisted with two Zeeman sextets and one doublet due to $Fe^{3+}$ ions. The jump up of magnetic hyperfine field of 2nd Zeeman sextet and the increasing of the values of quadrapole splitting and isomer shift of doublet below SP transition temperature could be interpreted with the variation of the superexchange interaction, the symmetry of lattice sites and the covalency of bonds due to the atomic displacements.

• Journal of the Korean Magnetics Society
• /
• v.7 no.3
• /
• pp.140-145
• /
• 1997

The amorphous state of $NdFe_{10.7}TiB_{0.3}$ and its nanocrystallization have been studied by X-ray diffraction, 모스바우어 spectroscopy, and a vibrating sample magnetometer (VSM), $NdFe_{10.7}TiB_{0.3}$ amorphous ribbons were fabricated by a sigle-roll melt-spinning method. The average hyperfine field $H_{hf}$(T) of the amorphous state shows a temperature dependence of $[H_{hf}(T)-H_{hf}(0)]/H_{hf}(0)=-0.46(T/T_c)^{3/2}-0.34(T/T_c)^{5/2}$ for $T/T_c<0.7$ indicative of spin wave excitation. The quadrupole splitting just above the Curie temperature $T_c$ is 0.46 mm/s, whereas the average quadrupole shift below $T_c$ is zero. The Curie and crystallization temperatures are determined to be $T_c$=380K and $T_x=490K$, respectively, for a heating rate of 5 K/min. The occupied area of nanocrystalline phase at around 770K is about 65%. Above the Curie temperature, VSM data show magnetic moments increases again. The formation of $\alpha$-Fe is the main reason for the increasing moment as conformed with the 모스바우어 measurements.

• Korean Journal of Materials Research
• /
• v.11 no.1
• /
• pp.3-7
• /
• 2001

$M\"{o}ssbauer$ spectra of the $Ni_{1+x}Ti_xFe_{2-2x}O_4$ systems ($0{\leqq}x{\leqq}0.7$), which appear as single phase spinel structure, were examined at RT. The $M\"{o}ssbauer$ spectra reveal two sextet for $0{\leqq}x{\leqq}0.3$, two sextet and a doublet for $0.4{\leqq}x{\leqq}0.6$, and a doublet for x=0.7 As x increases, the area ratio of B-site and A-site($A_B/A_A$) of the sextet decreases, and the area ratio of the doublet and the total areas($A_{doublet}/A_{tot.}$) increases. The isomer shift(I.S.) of A-site slightly increases and magnetic hyperfine fields($H_{hf}$) of two sites decrease as the increasing x. From these results, we have obtained the cation distributions of the samples and concluded that the increasing x leads to the decrease of covalency of $Fe^{3+}-O^{2-}$ bond in A-sites and A-B superexchange interactions.eractions.