Nai-li Di

Mössbauer spectra of CoZn-substituted Z -type barium ferrite Ba 3 Co 2 − x Zn x Fe 24 O 41

Mossbauer spectra of powder and aligned Ba3Co2-xZnxFe24O41 samples with x=0-2.0 have been obtained and analyzed at room temperature and at T=7 K with applied magnetic fields of 0 and 60 kOe. The relationship between Mossbauer parameters and magnetic properties has been studied. The magnetocrystalline anisotropy of Ba3Co2-xZnxFe24O41 is modified from the c plane to the c axis at Zn concentration x=1.2-1.6, based on the dependence of the quadrupole splitting and hyperfine field on Zn substitution for powder samples, and the values of the angle factor b for aligned samples. Zn ions occupy only sites with down spin, while Co ions prefer sites with up spin. As the Zn substitution increases, the increase in saturation magnetization is attributed to the occupation of Zn ions at sites with down spin, which decreases the negative magnetization, thus increasing the net magnetization.

Applied field Mossbauer study of shape anisotropy in Fe nanowire arrays

In order to investigate the magnetic anisotropy of Fe nanowire arrays from microscopic point of view, Fe57 Mossbauer spectra were measured at various magnetic fields along and perpendicular to the nanowire axis, respectively. On the basis of the absorption intensities of the second and the fifth lines of sextet, the orientation of Fe magnetic moments can be detected. It was found that the shape anisotropy dominates the overall magnetic anisotropy in the Fe nanowires. Furthermore, the longitudinal and transverse demagnetizing fields of Fe nanowire, respectively, were deduced from the effective hyperfine field at Fe57 nuclei as a function of applied field. The chain-of-spheres model in conjunction with symmetric fanning mechanism was adopted to interpret the domain structure and the parallel coercivity of magnetic nanowire arrays.

Mössbauer effect probe of local Jahn-Teller distortion in Fe-doped colossal magnetoresistive manganites

The local structure of the Fe-doped La1−xCaxMnO3 (x=0.00–1.00) compounds has been investigated by means of Mossbauer spectroscopy. 57Fe Mossbauer spectra provide direct evidence of Jahn–Teller distortion in these manganites. On the basis of the Mossbauer results, the Jahn–Teller coupling was estimated. It is noteworthy that the Ca-concentration dependence of the Jahn–Teller coupling strength is very consistent with the magnetic phase diagram. Our results reveal that Mossbauer spectroscopy cannot only detect the local structural distortion, but also provide a technique to investigate the Jahn–Teller coupling of Fe-doped La1−xCaxMnO3 colossal magnetoresistive perovskites.

Mössbauer effect probe of field-induced magnetic phase transitionin LaFe13−xSix intermetallic compounds

Direct evidence of a field-induced magnetic phase transition in LaFe13−xSix intermetallics with a large magneticaloric effect was provided by Fe57 Mossbauer spectra in externally applied magnetic fields. Moreover, Mossbauer spectra demonstrate that a magnetic structure collinear to the applied field is abruptly achieved in LaFe11.7Si1.3 compound once the ferromagnetic state appears, showing a metamagnetic first-order phase transition. In the case of LaFe11.0Si2.0, the Fe magnetic moments rotate continuously from a random state to the collinear state with increasing applied field, showing that a second-order phase transition is predominant. The different types of phase transformation determine the magnetocaloric effects in response to temperature and field in these two samples.

Low-field-induced magnetic entropy change in single-crystal Nd0.47Sr0.53MnO3

In this work, the discovery of a large low-field-induced magnetic entropy change in single-crystal Nd0.47Sr0.53MnO3 with A-type layered antiferromagnetic structure is reported. The magnetic entropy changes reach values of 11.0 and 11.5?J?kg?1?K?1 for field changes of 20?kOe along the ab-plane andc-axis, respectively. The large magnetic entropy change occurring near TN was attributed to a low-field-induced antiferromagnetic ferromagnetic phase transition. Our results provide a possibility for development of magnetic refrigerant substances that are operable with a permanent magnet rather than a superconducting one as the magnetic field source.

Atomic occupancy preference of Ga and Ti and its effect on the Mn spin arrangements in YMn6Sn6: Evidence from119Sn Mossbauer spectroscopy

Abstract The effects of Ga and Ti substitutions for Sn on the Mn spin arrangements in the YMn6Sn6 compound have been investigated by means of X-ray diffraction (XRD), magnetization measurement and Mössbauer spectroscopy. XRD refinement indicates that Ga and Ti atoms prefer to occupy 2d and 2e sites, respectively. Mössbauer spectra indicate incommensurate magnetic structures for the YMn6Sn6, YMn6Sn5.4Ga0.6 and YMn6Sn5.4Ti0.6 compounds. The substitution of Ga for Sn at the 2d sites is found to significantly decrease the turn angle in the Mn–Sn3–Sn2–Sn3–Mn layer and to subsequently increase the net magnetization. On the other hand, the substitution of Ti for Sn at 2e sites increases the turn angles in the Mn–(Y,Sn1)–Mn and Mn–Sn3–Sn2–Sn3–Mn layers, and consequently decreases the exchange coupling of Mn–Mn between different layers. The resulting ferromagnetic and ferrimagnetic behavior, as has been observed for YMn6Sn5.4Ga0.6 and YMn6Sn5.4Ti0.6, respectively, can be explained in terms of these spin interactions.

Mössbauer Studies of Fe-doped La-Ca-Mn-O Colossal Magnetoresistive Perovskites

The discovery of colossal magnetoresistance (CMR) in the manganite perovskites La1-xCaxMnO3 has recently attracted significant scientific attention[1,2]. A local structural distortion of MnO6 octahedron resulting from the Mn Jahn-Teller effect was assumed to play an important role in determining the resistivity behavior and the magnetic transition temperature[3]. Since the longrange structural distortion decreases rapidly in La1-xCaxMnO3 compounds with increasing Ca concentration, a local structural probe is required to analyze the distortion of the MnO6 octahedron. Mössbauer spectroscopy is a powerful technique for investigating the hyperfine interactions. One of the hyperfine parameters, the quadrupole splitting (∆) is very sensitive to the distribution of surrounding electrons of resonant nuclei. A few percent of Fe, which substitutes for Mn in La1xCaxMnO3 compounds, can be used as a micro-probe to detect the symmetry of the nearest-neighbor O ions in the Mn(Fe)O6 octahedron. Since Mn 3+ ions are mainly replaced by Fe ions in this Fedoping range and both ions have identical ionic radii in six-fold octahedral coordination [4], the substitution of Fe for Mn does not change the tolerance factor, and consequently, the Jahn-Teller effect can be investigated separately. In this work, we summarized the application of Mössbauer spectroscopy in La-Ca-Mn-O CMR pervoskites. The local structural distortion and Jahn-Teller coupling have been determined by Mössbauer spectroscopy on the basis of quadrupole splitting. Furthermore, the connection between Jahn-Teller coupling and CMR effect has been discussed.