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Magnetic Frustration Effects in the New Colossal Magnetoresistance Oxide NaCr2O4
Hikaru Takeda,Yasuhiro Shimizu,Masayuki Itoh,Hiroya Sakurai,Eiji Takayama-Muromachi 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
We have investigated the magnetic properties of the new colossal magnetoresistance oxideNaCr2O4 with the calcium-ferrite-type structure by using 23Na, 53Cr nuclear magnetic resonance(NMR) and magnetization measurements. This chromate is found to show an antiferromagneticorder with the spin moments slightly canted from the b axis at temperatures below TN=125 K. The spin structure may be governed by the competition between double-exchange ferromagneticand superexchange antiferromagnetic interactions in the double chains. The origin of the largemagnetoresistance is discussed for several scenarios such as phase separation, rearrangement of thespin structure induced by the magnetic field, and domain walls.
Kawada Hiroshi,Goshima Satoshi,Sakurai Kota,Noda Yoshifumi,Kajita Kimihiro,Tanahashi Yukichi,Kawai Nobuyuki,Ishida Narihiro,Shimabukuro Katsuya,Doi Kiyoshi,Matsuo Masayuki 대한영상의학회 2021 Korean Journal of Radiology Vol.22 No.4
Objective: To assess the noncontrast two-dimensional single-shot balanced turbo-field-echo magnetic resonance angiography (b-TFE MRA) features of the abdominal aortic aneurysm (AAA) status following endovascular aneurysm repair (EVAR) and evaluate to detect endoleaks (ELs). Materials and Methods: We examined four aortic stent-grafts in a phantom study to assess the degree of metallic artifacts. We enrolled 46 EVAR-treated patients with AAA and/or common iliac artery aneurysm who underwent both computed tomography angiography (CTA) and b-TFE MRA after EVAR. Vascular measurements on CTA and b-TFE MRA were compared, and signal intensity ratios (SIRs) of the aneurysmal sac were correlated with the size changes in the AAA after EVAR (AAA prognoses). Furthermore, we examined six feasible b-TFE MRA features for the assessment of ELs. Results: There were robust intermodality (r = 0.92–0.99) correlations and interobserver (intraclass correlation coefficient = 0.97–0.99) agreement. No significant differences were noted between SIRs and aneurysm prognoses. Moreover, “mottled high-intensity” and “creeping high-intensity with the low-band rim” were recognized as significant imaging findings suspicious for the presence of ELs (p < 0.001), whereas “no signal black spot” and “layered high-intensity area” were determined as significant for the absence of ELs (p < 0.03). Based on the two positive features, sensitivity, specificity, and accuracy for the detection of ELs were 77.3%, 91.7%, and 84.8%, respectively. Furthermore, the k values (0.40–0.88) displayed moderate-toalmost perfect agreement. Conclusion: Noncontrast MRA could be a promising imaging modality for ascertaining patient follow-up after EVAR.