• Journal of Magnetics
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• v.16 no.2
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• pp.173-176
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• 2011

Fe-Cr alloys with different Cr contents were prepared by an arc melting technique. The alloys were isochronally aged in the range from $400^{\circ}C$ to $900^{\circ}C$ with $50^{\circ}C$ steps with a holding time of 100 hours. The ageing produced embrittlement in the alloys due to either the formation of a Cr-rich ${\alpha}'$ phase or a $\sigma$ phase at high temperatures. Magnetic Hysteresis Loop (MHL) and Micro-Vickers hardness were measured at each step to correlate the magnetic and mechanical properties. Coercivity and hardness of the alloys were increased and remanence decreased up to 500-$550^{\circ}C$ due to formation of a Cr-rich ${\alpha}'$ phase. Beyond 500-$550^{\circ}C$ range, the coercivity and hardness decreased and remanence increased due to the coarsening or dissolution of the Cr-rich ${\alpha}'$ phase. In the Fe-48% Cr alloy, formation of the $\sigma$ phase at $700^{\circ}C$ reduced the maximum induction of the alloy significantly.

• Journal of the Korean Magnetics Society
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• v.13 no.5
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• pp.211-215
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• 2003

We fabricated the synthetic ferrimagnetic layers (SyFL) of permalloy/X (X=Ru, V)/permalloy by varying the X thickness, and investigated the changes of coercivity (H$\sub$c/), spin flopping field (H$\sub$sf/), and saturation magnetization field (H$\sub$s/) with a superconducting quantum interference device (SQUID). We also observed the microstructure with a cross sectional transmission electron microscope (TEM). Permalloy SyFL had less than 10 Oe coercivity, and H$\sub$sf/ and H$\sub$s/ could be tuned by varying ruthenium and vanadium layer thickness. The comparatively small exchange coupling in permalloy-V SyFL was caused by the intermixing of permalloy and vanadium decreasing the effective exchange coupling thickness.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1475-1477
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• 2001

In odor to set high saturation magnetization and coercivity, it had need to orient axis of easy magnetization of CoCr-based thin film perpendicular direction(c-axis) to the substrate plane. It was known that crystalline orientation of CoCr-based thin film was improved by introducing underlayer like Ti, Ge. We prepared singlelayer and double layer with Si underlayer by Facing Targets Sputtering System. As a result, intensity and c-axis dispersion angle ${\Delta}{\theta}_{50}$ of singlelayer were improved with increasing film thickness. Also, it was found that CoCr/Si and CoCrTa/Si double layer showed good c-axis dispersion angle due to introducing Si.

• Journal of Magnetics
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• v.16 no.2
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• pp.145-149
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• 2011

The coercivity $H_c$ of $Nd_2Fe_{14}B$ magnets and $Nd_2Fe_{14}B/(Nd_{0.7}Dy_{0.3})_2Fe_{14}B$ composite magnets were calculated by computer simulation based on the micromagnetic theory under assumptions that $Nd_2Fe_{14}B$ and $(Nd_{0.7}Dy_{0.3})_2Fe_{14}B$ grains have magnetically deteriorated layers on their surfaces and diffusion of Dy from $(Nd_{0.7}Dy_{0.3})_2Fe_{14}B$ grains to $Nd_2Fe_{14}B$ ones through the contacting boundaries recovers the magnetic anisotropy of the deteriorated layers of $Nd_2Fe_{14}B$ grains. $H_c$ of $Nd_2Fe_{14}B/(Nd_{0.7}Dy_{0.3})_2Fe_{14}B$ composite magnets increased by the diffusion of Dy from $(Nd_{0.7}Dy_{0.3})_2Fe_{14}B$ grains to $Nd_2Fe_{14}B$ ones and the resultant recovery of the anisotropy field of deteriorated layers of $Nd_2Fe_{14}B$ grains. The $H_c$ vs fraction of $(Nd_{0.7}Dy_{0.3})_2Fe_{14}B$ grains curve were convex for the magnets with the degree of alignment between 0.94 and 0.99, which suggests that the above composite magnets have larger $H_c$ values than the alloy-magnets with the same Dy content, and that we can save the consumption of Dy by using these composite magnets.

• Journal of the Korean Magnetics Society
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• v.6 no.4
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• pp.199-203
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• 1996

To study the magnetization reversal behavior of Co/Pd multilayers, we first demagnetized the samples by the field-demagnetized method and then measured initial curves and minor loops. The coercivity and the perpendicular magnetic anisotropy were obtained from the perpendicular and parallel magnetization curves measured at different temperatures. We interpret our experimental results by applying several qualitative and semiquantative approaches. From these study, we found that the magnetization reversal behavior is dominated by the domain wall pinning for all samples and the coercivity incremental tendency can be explained by Kronmuller's formula $H_c(T)\;{\propto}\;r_0.K_u$.

• Journal of Magnetics
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• v.16 no.3
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• pp.225-228
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• 2011

Magnetic properties and Rockwell hardness of 1Cr-0.5Mo steel have been investigated as a function of isothermal aging time. Our results showed that coercivity, hysteresis loss and Rockwell hardness in the aged samples decreased as aging time increased. This phenomenon was analyzed using optical microscopy and scanning electron microscopy. A significant diffusion of Cr and Mo atoms formed $M_2C$ and $M_7C$ carbides, lowering the matrix strength. $M_2C$ and $M_7C$ carbides partially segregated inside grains, diffused into grain boundaries, and finally resulted in a soft ferrite matrix and a hard grain boundary. The magnetic and mechanical softening of the matrix is likely to govern the properties of the sample more than the hardening of the grain boundary by carbide precipitations.

• Journal of the Korean Magnetics Society
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• v.2 no.1
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• pp.15-21
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• 1992

Acicular ${\gamma}-Fe_{2}O_{3}$ particles were heated at $90^{\circ}C$ in alkaline solution containing mixed solution of dyadic metal with $Co^{+2}/Fe^{+2}$ ratio of 0.5. When cobalt content was increased, the coercivity of resultant product increased linearly, and surface area decreased. The cobalt ferrite was grown epitaxially on the surface ${\gamma}-Fe_{2}O_{3}$ crystal, and the increase of coercivity was attributed to the crystalline magnetic anisotropy of the cobalt ferrite which is conform to coating layer. We can expect superior magnetic properties above normal ratio of 2. The progress of reaction has an effect on coercivity of cobalt ferrite epitaxial iron oxide. The stability of temperature and the change om standin& of $Co-{\gamma}-Fe_{2}O_{3}$ was largely influenced by the composition of coating layer.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.203-206
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• 2001

The effects of SrTiO$_3$ addition and sintering temperature on the microstructure and magnetic properties of yttrium iron garnet (YIG) were investigated. The lattice Parameter increasing of sintered YlG with small amount of SrTiO$_3$ addition was supposed to be substituted $Y^{+3}$, Fe$^{+3}$ ions to Sr$^{+2}$,Ti$^{+4}$ ions which are relatively large in ionic ranius. A YIG specimen sintered at 142$0^{\circ}C$ with 0.2mol% SrTiO$_3$ showed above 98% densification of theoretical density. Saturation magnetization (M$_s$) at room temperature decreased a little bit with increasing SrTiO$_3$, addition but no great chance. In addition, the coercivity (H$_c$) was almost not changed by sintering temperature.

• Journal of the Korean Magnetics Society
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• v.18 no.3
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• pp.98-102
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• 2008

Dependence of the exchange bias and coercivity as surface magnetic anisotropy and ferromagnet materials for $[Pd/Co]_N$ and $[Pd/Co,(CoFe)]_N$/FeMn multilayers with perpendicular magnetic anisotropy were investigated. The coercivity was proportionally increased to 670 Oe by increasing stack number N in Ta(2.1 nm)/[Pd(3.1/N)/$Co(1.2/N)]_N$/Ta(2.1) multilayers with perpendicular magnetic anisotropy. Also, the coercivity in exchange biased multilayer was tend to increased by increasing stack number N. But coercivity of each materials have been in order of Co (600 Oe), $Co_5Fe_5$ (520 Oe) and $Co_8Fe_2$ (320 Oe) as function of the ferromagnet materials. The other side, exchange force of each materials is 300 Oe when the reiteration layer number N is 3. In over number of reiteration layer 3, they maintained coercivity between 200 Oe and 300 Oe.

• Journal of the Korean Magnetics Society
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• v.21 no.4
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• pp.132-135
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• 2011

The exchange bias field ($H_{EX}$) and the coercivity ($H_C$) variation and change depending on the thickness of intermediately super-soft magnetic NiFeCuMo layer with different thickness of the bottom NiFe layer were investigated. The $H_{EX}$ of triple pinned NiFe(4 nm)/NiFeCuMo($t_{NiFeCuMo}$= 1 nm)/NiFe(4 nm)/FeMn multilayer has the maximum value more less than one of single pinned NiFe(8 nm)/FeMn layer. If NiFeCuMo layer is inserted each into between the pinned and free NiFe layers, we can be used as GMR-SV device for a bio-sensor that has improved magnetic sensitivity.