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High-Temperature Superparamagnetism in Boron Substituted Fe–Zr–Mn Alloys
Ulyanov, A.N.,Yu, S.-C.,Kang, Y.-M.,Yoo, S.-I. IEEE 2005 IEEE transactions on magnetics Vol.41 No.10
A magnetization and electron spin resonance study of amorphous Fe <TEX>$_82$</TEX> Mn <TEX>$_8-x$</TEX> B <TEX>$_x$</TEX> Zr <TEX>$_10$</TEX> <TEX>$(x=6, 8)$</TEX> ribbons is presented and discussed. Curie temperature of an amorphous matrix increased with <TEX>$x$</TEX> and equaled 302 K and 368 K for <TEX>$x=6$</TEX> and <TEX>$x=8$</TEX> alloys, respectively. A single resonance peak in ferromagnetic resonance (FMR) spectra was observed below Curie temperature, <TEX>$T_ C$</TEX> , and at least two distinct resonance lines were well observed at temperatures higher than <TEX>$T_ C$</TEX> . The low and high field-resonance lines were attributed to the paramagnetic state of the amorphous matrix and superparamagnetic states of nanoparticles embedded into the matrix, respectively. These observations could be qualitatively understood in terms of a finite-spin cluster plus an infinite ferromagnetic matrix model.
Ulyanov, A N,Kim, J S,Shin, G M,Kang, Y M,Yoo, S I Institute of Physics [etc.] 2007 Journal of Physics. D, Applied Physics Vol.40 No.1
<P>A giant magnetocaloric effect was found in La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB> manganite at low magnetic fields. The magnetic entropy changes caused by a magnetic field change of 0.5 and 1.0 T were as large as 5.04 and 6.25 J kg<SUP>−1</SUP> K<SUP>−1</SUP>, respectively, which exceed those of perovskite-like magnetic refrigerants or elemental Gd by a factor of 2–3. The extremely high values of the magnetocaloric effect are attributed to a sharp drop in the magnetization at a first-order ferromagnetic–paramagnetic phase transition and <I>S</I>-shaped magnetization versus field dependence.</P>
Kang, Young-Min,Ulyanov, Alexander N.,Yoo, Sang-Im WILEY-VCH Verlag 2007 Physica status solidi. PSS. A, Applications and ma Vol.204 No.3
<P>FMR linewidths of Y<SUB>3</SUB>Fe<SUB>5</SUB>O<SUB>12</SUB> (YIG) films fabricated by ex situ post-annealing of amorphous films deposited by radio frequency magnetron sputtering are reported. Amorphous YIG films were deposited on both thermally oxidized Si(100) and Gd<SUB>3</SUB>Ga<SUB>5</SUB>O<SUB>12</SUB> (GGG) (111) substrates and subsequently crystallized by ex situ post-annealing (600–900 °C) in two different oxygen atmospheres (air and 500 ppm O<SUB>2</SUB>). The compositions of as-deposited films were very sensitive to the oxygen partial pressure (P<SUB>O<SUB>2</SUB></SUB>) of the sputtering gas. During the post-annealing process, crystalline YIG phase started to grow upward on the substrates. High-quality YIG films showing narrow FMR linewidths (ΔH) of 5.3 and 70 Oe for GGG and thermally oxidized Si substrates, respectively, could be grown from the amorphous films deposited in pure Ar gas, composed of the cation ratio (Y:Fe = 3.04:4.96) close to the stoichiometric YIG. A reduced oxygen annealing atmosphere was found more effective than air for obtaining narrower FMR linewidths. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>