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External Field Dependence of Fe57 NMR in Pure Iron
Joonghoe Dho,Mincheol Kim,Soonchil Lee,Wonjong Lee,Yoonbae Kim 한국자기학회 1996 Journal of Magnetics Vol.1 No.1
The NMR spin echo in pure iron was measured as a function of external magnetic field up to 10 kgauss at room temperature. We observed the signal coming from a single domain formed over 7.5 kgauss which has not been detected in previous works. The resonance frequency shift with external field confirmed that the hyperfine field in iron is - 330.2 kgauss. From the comparison of the magnetization curve with the domain wall signal and the resonance frequency in external field, we showed that NMR could give the useful qualitative information on the magnetization process. The extent of the internal strain removed by annealing, which can be hardly seen in hysteresis curves, was clearly shown up in the NMR line-width.
Joonghoe Dho 한국자기학회 2005 한국자기학회 학술연구발표회 논문개요집 Vol.15 No.2
The resilience of the exchange bias (H_(Ex)) in ferromagnet / antiferromagnet bilayers is generally studied in terms of repeated hysteresis loop cycling or by protracted annealing under reversed field (training and long-term relaxation respectively). The stability of H_(Ex) is fundamental for practical application of exchange bias systems. In this paper we report measurements of training and relaxation in FeNi films coupled with the antiferromagnet FeMn. We show that H_(Ex) suppressed both by training and relaxation was partially recovered as soon as a field cycling for consecutive hysteresis loop measurement was stopped or the magnetization of the ferromagnet was switched back to the biased direction.
Dho, Joonghoe,Kim, Byeonggeon,Ki, Sanghoon IEEE 2016 IEEE transactions on magnetics Vol.52 No.7
<P>(100) Fe3O4 films were grown on five different (100)-oriented substrates: MgO, MgAl2O4 (MAO), (PbMg0.33Nb0.67)(1-x):(PbTiO3)(x) (PMNT), SrTiO3 (STO), and (LaAlO3)(0.3)(Sr2AlTaO6)(0.7) (LSAT), to investigate the substrate effects on structural, magnetic, and transport properties of the films. The X-ray diffraction measurements suggested that the epitaxial (100) Fe3O4 films were grown, although the lattice mismatch between the Fe3O4 and the substrates varied from +0.25% to -7.8%. Remarkably, the (100) Fe3O4 films grown on MAO, PMNT, and STO substrates exhibited a distinctive in-plane magnetic anisotropy with the magnetic easy axis along the [010] and [001] directions. In contrast, the (100) Fe3O4 films on the MgO and LSAT substrates showed a very weak anisotropy in the [011] easy direction. The Verwey transition temperature of the (100) Fe3O4 film was found to have a minimum value of similar to 110 K for MgO and a maximum value of similar to 122 K for STO. These results suggest that the magnetic anisotropy and Verwey transition behaviors of the (100) Fe3O4 film can be tuned by film growth on a specific substrate.</P>
Joonghoe Dho 한국자기학회 2008 Journal of Magnetics Vol.13 No.4
A very simple a.c. magnetic susceptometer for use in a helium closed cycle cryostat is reported in this paper. This simple setup has only a single bobbin-less copper coil, instead of the primary coil and two secondary coils typically used in mutual-inductance types. The single bobbin-less copper coil is directly mounted on the cryostat cold head. A sample is attached on the inside wall of the copper coil using a thermal contact material and its a.c. magnetic susceptibility is obtained from the measurement of the self-inductance of the sample coil using an LCR meter or an impedance analyzer. Experimental details are described and illustrative measurements on magnetic and superconducting materials as a function of temperature are included. The performances and limitations of this simple a.c. magnetic suceptometer are also discussed.