J. Przewoźnik

Solid solutions TbFe1−xAlxO3 (0 ⩽ x ⩽ 1): Structure and magnetic behaviour☆

Abstract Magnetic X-ray, neutron diffraction and DSC measurements for a solid solution of the TbFe 1− x Al x O 3 system have been carried out. The results obtained indicate an essential role for Al substitutions on the magnetic behaviour of the compounds examined. For low Al concentration, a radical reduction of magnetic susceptibility of the compounds has been observed. The increase in Al concentration ( x = 0.4−0.7) generates a compensation temperature (∼35 K) in the system. This effect is responsible for the change in the type of Tb-Fe coupling (from ferromagnetic to antiferromagnetic).

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.

X-Ray diffraction and 155Gd-Mössbauer effect study of GdMn2Hx (0≤x≤4.3)

Abstract X-Ray diffraction and 155Gd-Mossbauer effect were applied to study the structural, electronic and magnetic properties of GdMn2Hx with x = 0, 0.5, 1.0, 2.0, 2.5, 3.4 and 4.3. The XRD studies performed between 12 and 300 K reveal the existence of defined phases with cubic or rhombohedrally distorted C15 structure. The 155Gd isomer shift, quadrupole interaction and hyperfine field clearly reflect the electronic and magnetic modifications of the Gd site by the hydrogen uptake.

Magnetic and structural properties of DyMn2Hx (0≤x≤4.2)

Abstract The magnetic properties of Dy( 57 Fe 0.01 Mn 0.99 ) 2 H x compounds were investigated by means of 57 Fe Mossbauer spectroscopy and temperature dependent magnetic susceptibility (DC, AC) and magnetisation measurements. Their structural properties in the temperature range 70 K≤ T ≤400 K were studied by means of powder X-ray diffraction. It was found that, at room temperature, the lattice parameters increase continuously upon hydrogen absorption in the 0.8≤ x ≤3.5 range and the cubic C15 crystal structure is preserved. At 70 K the system differentiates into several distinct hydride phases and two-phase ranges. The lattice expansion together with the chemical effect of hydrogen results in dramatic changes in the properties of the hydrides as compared to the host compound. By means of 57 Fe Mossbauer spectroscopy, values of the average isomer shifts at 4.2 and 300 K and the average hyperfine fields at 4.2 K were determined. From isomer shift changes at room temperature, the relative importance of the volume expansion and band effects due to hydrogen absorption were deduced. A nonlinear increase of the magnetic ordering temperatures T M versus x and an abrupt increase of the average hyperfine fields for x ≥2.5 were also found. Based on T M values for Y( 57 Fe 0.005 Mn 0.995 ) 2 H x as reference the magnitude of the 4f–3d indirect interaction was inferred. In addition, a strong decrease of this interaction with increasing x (resulting in its cancellation for x >2.8) and a weak dependence on the Dy–Mn distance are clearly shown.

Magnetostructural transition and magnetocaloric effect in highly textured Ni-Mn-Sn alloy

Ni49.4Mn38.5Sn12.1 near single crystal was obtained by the Bridgman method. At room temperature, it consisted of a mixture of the parent austenite phase with the cubic L21 Heusler structure (ac = 5.984 A) and modulated, tetragonal martensite phase 4M (at = 4.337 A, ct = 5.655 A). Under the application of a magnetic field, the specimen undergoes field induced reverse martensitic transformation, which combined with the Curie transition in austenite leads to the coexistence of direct and inverse magnetocaloric effects. The maximum entropy change at 280 K and under 5 T amounts to 3.4 J·kg−1·K−1 for the structural transition and at 316 K reaches −2.7 J·kg−1·K−1 for the magnetic transformation. The magnetic entropy change occurs over a wide temperature span leading to improved refrigerant capacity of 101 J·kg−1 (5 T). Hysteretic losses are considerably reduced, which is promising with respect to improved cyclic stability of such a material.

Spin reorientation in the Er2−xFe14+2xSi3 single crystal studied by the Fe57 Mössbauer spectroscopy and magnetic measurements

Spin reorientation in the single crystal of Er2−xFe14+2xSi3 with x=0.25(5) has been studied in the temperature range of 4–300K by means of the magnetic measurements and Mossbauer spectroscopy on Fe57 by using the 14.41keV resonant transition. The bulk magnetic moment has been measured versus applied field up to ±8.9T along the c axis of the P63∕mmc cell at 4K. The hysteresis loop has been measured at 300K for the external field applied along the c axis. The bulk moment has been measured versus temperature in the moderate external field of 0.1T applied along the c axis. The ac susceptibility has been measured for several frequencies and amplitudes of the ac field applied along the c axis versus temperature either in the null external field or in the external field of 0.1T along the c axis. Mossbauer measurements were performed versus temperature on the powder sample and single crystal with the radiation beam oriented along the c axis. The spin reorientation from the [a−b] plane onto the c axis occurs for a...

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.

Thermodynamic Properties of RZnSn2 (R = Y, Er, Lu) Compounds with HfCuSi2 Structure Type

The results of magnetic and specific heat studies are reviewed and discussed for the series of RZnSn2 (R = Y, Er and Lu) compounds crystallizing in the same tetragonal HfCuSi2 - type of structure. A sharp peak in the specific heat of ErZnSn2 compound is indicative for magnetic ordering of Er moments at 5.0 K, being in agreement with its established antiferromagnetic nature. The estimated magnetic entropy Smagn contribution is less than that expected for the ground state J = 15/2 multiplet of Er3+.

Magnetic Properties of the Bi6Fe2Ti3O18 Aurivillius Phase Prepared by Hydrothermal Method

The multiferroic Aurivillius phases in the Bi-Fe-Ti-O system are built from alternate (Bi2O2)2+ and (Bin-1XnO3n+1)2 layers, where X = Fe3+, Ti4+ and “n” refers to the number of perovskite-like layers between Bi2O2 layers. Detailed magnetic studies should be done to understand electromagnetic interactions and multiferroic coupling effects. In the present paper, a powder composed of the Aurivillius phase with n = 5, Bi6Fe2Ti3O18, was successfully prepared by the hydrothermal method. The powder was sintered, obtaining dense polycrystalline materials. It was stated that both powder and sintered bodies were paramagnets with a possible antiferromagnetic ordering or a spin-glass state at the liquid helium temperatures.

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.