K. Krop

Mössbauer study of magnetic ordering in GdMn2 and YMn2

Abstract The magnetic properties of GdMn 2 and YMn 2 were investigated by means of Mossbauer Spectroscopy at 57 Fe nuclei which substituted 0.5% of Mn atoms. Measurements were performed in the temperature range between 4.2 and 300 K. Gadolinium sublattice was monitored by 155 Gd(86.5 keV)-resonance at 4.2 K. Results show an evidence for two magnetic transitions at 40 and 100 K for GdMn 2 , but only one for YMn 2 , around 100 K. For both compounds B hf shows thermal hysteresis. A new Yafet-Kittel-type magnetic ground state ordering for GdMn 2 is proposed, which came out from the numerical solution of a set of coupled Brillouin equations written in terms of the molecular field approximation. Mossbauer effect results however are too compounded to be explained in details within the frame of this type of ordering.

Magnetism of DyMn2 and HoMn2 - 57Fe and 119Sn Mössbauer studies

Abstract Mossbauer spectra were measured for two Laves phase compounds DyMn 2 and HoMn 2 in which manganese was substituted to 0.5% with 57 Fe and to 0.2% with 119 Sn. At 4.2 K the 57 Fe and 119 Sn spectra of the Dy compound were unambiguously fitted each with two Zeeman patterns (with relative contributions to the spectra 3:1) corresponding to two different Mn sites — magnetic and nonmagnetic. Transferred hyperfine fields at 119 Sn were found to be proportional to the magnetic moment of Dy and its ferromagnetic component, corroborating the magnetic structure found in neutron diffraction (ND) experiment. The same procedure was carried on with the spectra measured for the Ho compound, but the above mentioned proportionality was not found.

Electronic states of La1−xCaxMnO3 from photoelectron spectroscopy

Abstract The electron photoemission spectra from core-levels as well as from the valence bands of the manganese perovskites La 0.67 Ca 0.33 MnO 3 , La 0.63 Ca 0.37 Mn 0.92 Fe 0.08 O 3 and (La 0.57 Tb 0.10 )Ca 0.33 MnO 3 have been measured in insulating paramagnetic state at 300 K. The valence band spectra show a two-peak structure at about 3.0 and 5.7 eV below the upper edge of the valence band. Comparing the spectra with the high-resolution spectra measured at 110 eV synchrotron radiation the strong hybridisation of Mn 3d–O 2p states contributing to the valence band has been confirmed. The higher binding energy part of valence band spectrum of Tb-doped specimen shows a third feature whose physical origin is discussed. The values of the on-site Coulomb correlation energies in Mn 3d states U dd , in O 2p states U pp , the charge transfer energy Δ and the hybridisation energy between Mn 3d and O 2p states T were estimated from the Mn 2p spectra and Auger spectra analysed together with the relevant valence band spectra. Some results are compared with the 55 Mn nuclear magnetic resonance data.

Mössbauer effect study of the magnetic order in YMn2Hx

Abstract By means of Mossbauer spectroscopy, values of magnetic ordering temperatures (TN,C), average isomer shift (S) at 300 K and average hyperfine field (Bhf) at 4.2 K were established for Y(57Fe0.005Mn0.995)2Hx (0 ≤ × ≤ 4.2). A perfect linear dependence of TN,C and S on the MnMn distance for x ≥ 1 and sharp increase of Bhf for x ≥ 2.6 was revealed. A tentative magnetic phase diagram is proposed.

Spin reorientation in Er2Fe17−xMnx - Mössbauer effect study

The polycrystalline samples of Er2Fe17−xMnx compounds have been studied by57Fe Mossbauer spectroscopy in the temperature range between 4.2K and 200K. A reorientation of the easy axis of magnetization has been evidenced for compound with x=4 in the measurements on magnetically oriented powdered sample. Spin reorientation from the c-axis to the basal plane is observed when temperature is increased above 105K.

The influence of hydrogen on55Mn hyperfine fields in YMn2 hydrides

The NMR spin ccho measurements at 4.2 K for YMn2Hx (x=1, 2, 3) compounds are reported. The obtained values of55Mn hyperfine fields are analysed in dependence on the by hydrogen atoms and flips of neighbouring manganese moments. The strong increase of hyperfine field with increasing number of the nearest hydrogen atoms is explained by the change of orbital contribution to hyperfine field.

Magnetism of hexagonal RMn2: 57Fe Mössbauer studies

Abstract RMn 2 compounds (R = Nd, Sm, Ho, Er, Tm and Th) with the Mn atoms substituted by 57 Fe were studied at 4.2 K. The nonmagnetic character of Mn in TmMn 2 and ErMn 2 and the existence of a mixed phase in HoMn 2 were confirmed. The absence of a self-magnetic moment on the 57 Fe probe at nonmagnetic Mn sites was found.

Mössbauer effect study of Y(57FeMn)2

YMn2 compound doped with57Fe was investigated using57Fe Mössbauer resonance in the temperature range 4.2–400 K. The magnetically split spectra were analyzed assuming two magnetically nonequivalent Fe sites with relative population dependent on iron concentration. In the transition temperature region a coexistence of the magnetic and nonmagnetic components was observed in the temperature span of about 50 K. A thermal hysteresis (of about 25 K) of the magnetic component confirms the first-order type magnetic transition. Temperature dependence of the hyperfine field of the magnetic component could be interpreted in terms of spin-fluctuation theory.

Magnetic and transport properties of Fe-substituted manganites La0.67Ca0.33Mn1−xFexO3

Abstract Specific heat, magnetic susceptibility and magnetoresistivity measurements have been performed on the polycrystalline samples of Fe-substituted manganites. The transition temperatures derived from the specific heat anomalies for x=0,0.01,0.06 were in agreement with the position of the maximum slope of AC susceptibility. For compositions with x=0.10 and 0.15 no transition was observed in the specific heat. A sharp increase in resistivity below 135 and 125 K was observed in zero field for x=0.10, and 0.15, respectively.

Moment formation in Y(57FeMn)2

Abstract X-ray diffraction and Mossbauer spectroscopy investigations are reported on YMn 2 doped with 1% Fe. Even at 4.2 K a part of the sample, where the Fe atoms are nonmagnetic, remains with the cubic structure. Fe atoms within the distorted structure exhibit antiferromagnetic exchange interaction.