Magnetism of Fe in SrFe 2 As 2 : Local investigation by time differential perturbed angular distribution (TDPAD) spectro
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Magnetism of Fe in SrFe2 As2 : Local investigation by time differential perturbed angular distribution (TDPAD) spectroscopy S. K. Mohanta · S. N. Mishra · S. M. Davane · Neeraj Kumar · A. Thamizhavel · S. Layek · Z. Hossain · S. K. Srivastava
© Springer Science+Business Media Dordrecht 2012
Abstract Employing the γ -ray perturbed angular distribution technique, we have measured the magnetic hyperfine field of 54 Fe in tetragonal and orthorhombic structural phases of SrFe2 As2 . In the tetragonal phase, the magnetic response of 54 Fe shows Curie-Weiss type local susceptibility, indicating the presence of localized moment on Fe. The temperature dependence of the hyperfine field of 54 Fe reflects quasi-two dimensional first order magnetic transition at 200 K. Our data indicate that Fe moments in the magnetically ordered phase of SrFe2 As2 may be canted out of the ab-plane. Keywords Pnictides · Hyperfine field · TDPAD · Critical phenomenon
1 Introduction Ferro-pnictides with chemical formula unit XFe2 As2 (X = Ca, Sr, Ba, and Eu), in recent years, have been in the fore front of research because of their intriguing structural and magnetic and structural properties [1–3]. These compounds with tetragonal unit cell at room temperature, show concomitant first order structural and magnetic phase transitions at temperature T0 varying from 138 K for BaFe2 As2
S. K. Mohanta · S. N. Mishra (B) · S. M. Davane · N. Kumar · A. Thamizhavel Tata Institute of Fundamental Research (TIFR), Homi Bhabha Road, Mumbai 400005, India e-mail: [email protected] S. K. Mohanta · S. K. Srivastava Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur 721302, India S. Layek · Z. Hossain Department of Physics, Indian Institute of Technology, Kanpur 208016, India
S.K. Mohanta et al.
to 200 K in SrFe2 As2 . Below T0 the compounds have orthorhombic structure and exhibit spin density wave (SDW) antiferromagntism (AF) [1–3]. Interest in these materials has grown many folds because they show superconductivity upon doping or application of external pressure [1–3]. It is widely believed that magnetic interactions play an important role on the electron pairing mechanism in these compounds [1–3]. In this regard, it is important to understand the magnetism of Fe, above and below the structural transition. The magnetism of Fe in the low temperature orthorhombic phase of these compounds has been studied in great details using variety of experimental techniques including nuclear methods like neutron diffraction, NMR, μSR and Mossbauer spectroscopy. While, many of the studies suggest a columnar antiferromagnetic structure commensurate with the crystal lattice [4–6], several others report an incommensurate AF ordering [7, 8]. As far the paramagnetic tetragonal phase, it is not clear whether Fe atoms carry local moment or not. Conventionally, local moment in paramagnetic state is determined from Curie-Weiss behavior of bulk magnetic susceptibility. However, determination of Fe local moment in paramagnetic state of 122 pnictides from
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