V.I. KRYLOV
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Resumo IPEN-doc 27087 Magnetic hyperfine field at 119Sn and 111Cd probes in Gd5Ge4 studied by Mössbauer and PAC spectroscopy2019 - KRYLOV, V.I.; BOSCH-SANTOS, B.; CABRERA-PASCA, G.A.; CARBONARI, A.W.; SAXENA, R.N.; LEITE NETO, O.F.S.The magnetic structure of Gd5Ge4 belonging to the family of giant magnetocaloric Gd5(Si1-xGex)4 alloys [1] has been examined by magnetization measurements in single crystal [2, 3], X-ray resonant magnetic scattering (XRMS) [4], and neutron powder diffraction (NPD [5]. Gd5Ge4 crystallizes in the orthorhombic structure (space group Pnma) having three non-equivalent Ge-sites. At low temperatures, the Gd magnetic moments are ferromagnetically (FM) aligned within the slabs along the c-direction, while their stacking in the b-direction is antiferromagnetic (AFM) below 127 K [2, 4]. In this work, the temperature dependence of the magnetic hyperfine field (HF) and electric quadrupole interaction on 119Sn and 111Cd probe nuclei in Gd5Ge4 compound have been investigated by Mössbauer and perturbed angular correlation (PAC) spectroscopy. At the saturation, the HF magnitudes reach of Bhf =28.0(5) T and Bhf= 12.6(5) T for 119Sn and 111Cd, respectively, which correspond to the FM local magnetic environment for these probes. It was found that 119Sn probes are placed in two Ge positions, whereas 111Cd probes are located in only one of the three Ge positions in Gd5Ge4. Temperature dependence of Bhf for both 119Sn and 111Cd probes in Gd5Ge4 present anomalous behavior. In the range from 20 K to 120K, the HF decreases almost linearly when temperature increases. These anomalous behavior of Bhf(T) for 119Sn and 111Cd probes are in agreement with the temperature variation of the magnetic (070) and (010) peak intensities that have been found in XRMS [3] and NPD [4] studies. The AFM ordering temperature of Gd5Ge4, TN=129(1) K, found from the Bhf (T) is in agreement with previous results of [2 - 5]. Changes of the values and sign of the quadrupole shift of Mössbauer spectra for 119Sn atoms with the increase of temperature from 30 to 50 K confirm the spin-flop transition in Gd5Ge4 [2, 4].Resumo IPEN-doc 23309 Temperature anomalies of the hyperfine magnetic fields on 111Cd probe nuclei in ferro- and antiferromagnetic phases of the ordered FeRh alloys2016 - KRYLOV, V.I.; BOSCH-SANTOS, B.; CABRERA-PASCA, G.A.; CARBONARI, A.W.; SAXENA, R.N.; MESTNIK-FILHO, J.FeRh ordered alloy crystallizes in the bcc B2 structure [1], presents first order phase transition from antiferromagnetic (AF) ordering at low temperature to ferromagnetic (F) state above 350 K [2], and shows significant magnetocaloric effect near RT [3]. Recently, FeRh alloy has also been considered as an interesting material for spintronics applications [4]. In the AF state, FeRh has compensated AFII-type magnetic structure with μFe=3.3 μB and μRh=0. In the F state of FeRh both Fe and Rh atoms have magnetic moments of μFe=3.2 μB and μRh=0.9 μB, respectively [5]. The Fe – Rh compounds were studied by Mössbauer spectroscopy (MS) on 57Fe [6, 7] and 119Sn probe nuclei [8]. In this work, we have, for the first time, investigated the HFs for 111Cd probe atoms in two FeRh samples of different composition by perturbed γ-γ angular correlation (PAC) spectroscopy in the range from 40 K to a temperature above the TC. The alloy Fe0.48Rh0.52 (A1 sample) is AF at low temperatures. At the temperature Tt = 345 K the first order phase transition is observed, and this compound becomes F at the temperatures lower than TC = 685 K. The alloy Fe0.52Rh0.48 (A2 sample) is only ferromagnetic below TC = 800 K. It was established that in both alloys 111Cd probes substitute only Fe ions. The HFs values extrapolated to 0 K were found to be B1(0) =8.70(5) T and B2(0) =5.53(5) T for AF and F ordering of A1 and A2 samples, respectively. The HF in the AF state is almost 60% higher than the HF in the F alloy. The dependences B1 (T) and B2 (T) show anomalous behavior. At Tt = 345 K, phase transition AF-F is accompanied by a sharp decrease in the HF at 111Cd probe nuclei. Earlier, an increase of the corresponding HFs was observed for 57Fe atoms and 119Sn impurity atoms in the region of AF-F transition by MS in [6] and [8]. Analysis of B1(T) and B2(T) has allowed to obtain the temperature dependences of the competing contributions BFe (T) and BRh (T) to the HFs on 111Cd probe nuclei in FeRh alloys.