In this study, we performed the first-principles electronic structure calculations within the density functional theory for the two-dimensional monolayer of 1T CrSe₂ based compounds to show that a substitution of Cr with heavier transition metals induces the stabilization of ferromagnetic phase and it’s closely related to the lattice constant increase. The structural optimization and total energy comparison of the paramagnetic, ferromagnetic (FM), and antiferromagnetic (AFM) phases of the pristine CrSe₂ single layer reveals that (1) the in-plane stripe AFM is the ground state while the energy difference between AFM and FM phases is relatively small (~0.03 eV/unit cell) and (ii) an in-plane strain inducing the increase of lattice constant by 2.7% can result in a magnetic phase transition stabilizing the FM state. In fact, we introduce a lattice increase by substituting 50% of 3d Cr with 4d and 5d transition metals, Zr and W, to make Cr_0.5Zr_0.5Se₂ and Cr_0.5W_0.5Se₂ and show that the FM magnetic phase is stabilized. Our calculation indicates that the substitutional doping by Zr results in the in-plane lattice constant increased by 6.8%, being more efficient in using the in-plain strain effect not only to stabilize the ferromagnetic phase but also to increase spin magnetic moment of Cr atom which plays critical role in determination of the magnetic property of the present material.

We grew TbMn₂O₅ thin films on Nb doped TiO₂(110) substrates at different temperatures and studied the influence of growth temperature on their physical properties. When the growth temperature was 700 ℃, the preferred crystal orientation perpendicular to the film surface was TbMn₂O₅(002) whereas it was turned to (211) with increasing the growth temperature to 950 ℃. For the sample with the growth temperature of 750 ℃, the domains with the crystal orientations of TbMn₂O₅(002) and TbMn₂O₅(211) were mixed. For magnetic properties, the phase transition from paramagnetic to ferromagnetic was observed at about 43K for all samples studied. However, the larger the coercive field and magnetic hysteresis were observed with decreasing the growth temperature. These observations indicate that the growth temperature is an important parameter in determining the crystal orientation and magnetic property of TbMn₂O₅ thin film.

It is very important to isolate soft magnetic particles electrically in order to reduce an eddy current loss of compressed cores. In this study, iron powders were oxidized in a mixed gas of N₂+H₂O at 600 ℃ in order to encapsulate the powders completely by iron oxide and compressed into cores. The oxide film was analyzed to be Fe₃O₄ by XRD as well as its color and grew linearly through oxidation. With increasing oxidation time, its permeability increased whereas the density decreased. The core, eddy current and hysteresis losses of the oxidized cores were much lower than those of the cores with insulating powders. It was confirmed that the Fe₃O₄ film formed in a damp atmosphere could encapsulate the iron particles completely and ensured lower eddy current loss.

We measured the permeability of amorphous CoFeB thin film by using second harmonic signals of planner Hall resistance (PHR) sensor. The permeability of amorphous CoFeB thin film measured using PHR sensor was constant value in the low frequency range of 10 Hz~50 kHz. The measured high frequency permeability of amorphous CoFeB thin film was analyzed by complex permeability equation in order to compare with the low frequency permeability. We confirmed that the constant value of low frequency permeability was correspond to the initial permeability of amorphous CoFeB thin film. Thus the PHR sensor could be used to the low frequency permeameter.

Planar hole resistance (PHR) and planar hole voltage (PHV) characteristics of circular IrMn-based giant magnetoresistance-spin valve (GMR-SV) type Ta/NiFe/CoFe/Cu/CoFe/IrMn/Ta multilayer films were investigated. The interlayer exchange coupling field, coerciviy, and magnetoresistance ratio of the GMR-SV multilayer were 12.0 Oe, 5.0 Oe, and 5.4%, respectively. The magnetoresistance ratio obtained from the PHR curve was 12.56% and the magnetic sensitivity was 0.63%/Oe. In the PHV curve, the linear slope (sensitive PHV, SPHV) was 120 μV/Oe due to the voltage difference of 2.4 mV in the external magnetic field ± 12 Oe. As the current value increased from 1.6 mA to 15.0 mA, both PHV and SPHV increased linearly. As a method of improving the sensitivity of the PHR sensor, it is proposed to control the thickness of the Cu layer which can reduce the interchange coupling force in the GMR-SV multilayer.

Z-type Sr-hexaferrites (Sr₃Co₂Fe_24+xO₄₁, x = -1.0, -0.5, 0.0, 0.5, 1.0) were prepared by solid-state reaction processes. XRD analysis revealed that almost single Z-type hexaferrite phase could be obtained at the Fe-deficient composition of x = -1.0. In SEM analysis, it is found that the grain size gradually decreases with increase of x. For the single phase Sr₃Co₂Fe_24+xO₄₁ (x = -1.0) powder samples, the Sr₃Co₂Z powder-epoxy-graphite composites were prepared with varying graphite amount (0.00, 1.25, 2.50, 3.75, 5.00 wt%). The height of real and imaginary part of permittivity spectra gradually increases with increasing the graphite amount, whereas the permeability spectra does not show significant variation with the graphite amount. The peak of imaginary part of permeability at ~3 GHz corresponds to the ferromagnetic resonance of the Z-type hexaferrites. The reflection loss (RL) which reflects the electromagnetic wave absorption performances was calculated as functions of frequency and thickness. The minimum RL values are in range of -53 dB~-38 dB and the frequency of minimum RL decreased from 3.18 GHz to 2.49 GHz with the increase of graphite addition.