Temperature Dependence of the Magnetic Hyperfine Field at 140Ce on Gd Sites in GdAg Compound

Perturbed gamma–gamma angular correlation technique was used to measure the magnetic hyperfine field at Gd sites in the intermetallic compound GdAg using the ¹⁴⁰La→¹⁴⁰Ce nuclear probe. A major and well-defined magnetic interaction is observed at ¹⁴⁰Ce substituting Gd sites in GdAg below 130 K, corresponding to a ferromagnetic ordering of Gd moments. The temperature dependence of magnetic hyperfine field, however, shows a sharp deviation from an expected Brillouin-like behavior for temperatures below 75 K. This additional magnetic interaction is believed to result from the polarization of Ce spin moments induced by the magnetic field from Gd atoms.     

Magnetoresistances and magnetic entropy changes associated with negative lattice expansions in NaZn13-type compounds LaFeCoSi

Magnetoresistances and magnetic entropy changes in NaZn13-type compounds La（Fel-xCox）11.9Si1.1 （x=0.04, 0.06, and 0.08） with Curie temperatures of 243 K, 274 K, and 301 K, respectively, are studied. The ferromagnetic ordering is accompanied by a negative lattice expansion. Large magnetic entropy changes in a wide temperature range from ～230 K to ～320 K are achieved. Raising Co content increases the Curie temperature but weakens the magnetovolume effect, thereby causing a decrease in magnetic entropy change. These materials exhibit a metallic character below Tc, whereas the electrical resistance decreases abruptly and then recovers the metal-like behaviour above Tc. Application of a magnetic field retains the transitions via increasing the ferromagnetic ordering temperature. An isothermal increase in magnetic field leads to an increase in electrical resistance at temperatures near but above Tc, which is a consequence of the field-induced metamagnetic transition from a paramagnetic state to a ferromagnetic state.     

Helicoidal magnetic structure of Ru2FeSi

Magnetic susceptibility, X-ray and neutron diffraction measurements have been performed on Ru₂FeSi intermetallic compound, which was found to be antiferromagnetic below 280 K. Neutron diffraction data obtained at 300 K indicate that Ru₂FeSi exhibits a chemically ordered structure with some admixture of L2₁ type of ordering. The magnetic ordering observed at 4.2 and 78 K consists of two components: - a collinear one formed by ferromagnetic (111) planes coupled antiferromagnetically, - an antiferromagnetic cone spiral with propagation vector k = 0.6a^*, parallel to the [001] direction. The total magnetic moment of 3.7μ_B at 4.2 K was found to be localized on iron ions only.     

New magnetic states in copper metaborate CuB<Subscript>2</Subscript>O<Subscript>4</Subscript>

The static and resonance properties of copper metaborate CuB₂O₄ were experimentally studied in a magnetic field applied in the crystal tetragonal plane. The field-induced second-order phase transition to a weakly ferromagnetic state was observed in the temperature range 10–20 K. The low-field state is characterized by the absence of spontaneous moment, and it represents, presumably, a long-period helicoid. At temperatures below 2 K, two sequential first-order phase transitions were observed. They were accompanied by jumps in resonance absorption with a hysteresis upon changing field-scan direction. These transitions can be caused by the transformation of the incommensurate spin structure into the helicoidal states with periods commensurate with the lattice translation period.     

Raman Spectroscopy and Magnetic Properties of Mn-Doped ZnO Bulk Single Crystal

Mn doped ZnO bulk single crystals are grown by the modified Bridgman method. The as-grown crystals are red in eolour. The additional Raman mode observed at 524cm^-1 is attributed to the Mn ions incorporating into ZnO crystal. The crystal exhibited paramagnetie under lower applied field below 2280 Oe. Then diamagnetism is observed in the crystal when the magnetic field rises up and becomes dominant under applied field above 5270 Oe. The magnetic susceptibility dependence on the temperature follows a Curie law indicating a typical paramagnetie characteristic under an applied field of 2kOe. No ferromagnetic ordering is observed in the as-grown Mn-doped ZnO crystal.     

Comment on magnetism and superconductivity in rutheno cuprates: RuSr2GdCu2O8 and RuSr2Gd1.5Ce0.5Cu2O10

Both RuSr₂GdCu₂O_8-δ (Ru-1212) and RuSr₂Gd_1.5Ce_0.5Cu₂O_10-δ (Ru-1222) exhibits magnetism and superconductivity, as seen by magnetization vs. temperature behavior measured in 5 Oe field. Zero-field-cooled (ZFC) and field-cooled (FC) magnetization data show branching at around 140 K and 100 K with a cusp at 135 K and 80 K and a diamagnetic transition around 20 K and 30 K in the ZFC part, for Ru-1212 and Ru-1222, respectively. The isothermal magnetization possesses a non-linear contribution due to a ferromagnetic component at low temperatures below 50 K for both samples. The resistance vs. temperature behavior of the samples in applied fields of 0, 3 and 7 T confirmed superconductivity, with a different type of broadening of the superconductivity transition under magnetic fields for Ru-1212 from that known for conventional high-T _c superconductors. The magnetoresistance (MR) is negative above the Ru magnetic ordering temperature at 135 K. Below the Ru magnetic ordering temperature, MR displays a positive peak at low fields and becomes negative at higher fields for Ru-1212. For Ru-1222, MR remains negative both above and below the ordering temperature. A maximum of 2% is observed for the negative MR value at the Ru magnetic ordering temperature. An electron diffraction pattern obtained for the Ru-1212 sample shows two types of superstructure: one has a weak spot at the centre of the a–b rectangle, and the other only along the b direction. Interestingly, Ru-1222 shows only clean a–b and a–c planes, without any superstructures.     

Rearrangement of crystallographic domains driven by magnetic field in antiferromagnetic CoO

The rearrangement was investigated of crystallographic domains in the antiferromagnetic pseudo-tetragonal phase in CoO (Néel temperature: 293 K) when the domains were driven by a magnetic field. A rearrangement is generally observed in ferromagnetic shape-memory alloys. The rearrangement was found to occur at temperatures between 170 K and 293 K, but not at temperatures below 170 K. In order to determine the reason for such a difference, the shear stress driven by a magnetic field, τ _mag, was calculated and compared with the shear stress required for twinning plane movement, τ _req. It was found that τ _mag is equal to or larger than τ _req whenever the rearrangement of crystallographic domains occurs due to the application of a magnetic field, and vice versa. This observation is similar to past observations in the case of many ferromagnetic shape-memory alloys.     

Ultrasonic study of dysprosium in a magnetic field

The ultrasonic attenuation of longitudinal waves propagating along the c axis of single crystal dyprosium is reported, as a function of the applied basal plane field in the paramagnetic region, and as a function of the temperature, at constant applied basal plane field, in the spin-spiral region. In the paramagnetic region, anomalous attenuation behavior is explained on the basis of competing spin-polarization and spin-fluctuation effects. Two anomalous maxima in the temperature dependence of the attenuation were observed: one near T_N is attributed to spin fluctuations associated with short range ferromagnetic ordering; another one at 130 K is attributed to a magnetic phase transition from a fanstructure phase, intermediate between the spin-spiral and ferromagnetically ordered phase     

Large variations in the magnetic ordering behavior of EuCu(2)As(2) with the application of external pressure and magnetic field

The influence of external pressure on the electrical transport and magnetic properties of EuCu(2)As(2), crystallizing in a ThCr(2)Si(2)-type structure, is reported. The system is known to be an antiferromagnet below T(N) ≈ 15 K in the absence of external magnetic fields. We find that there is a gradual reduction of T(N) with the application of a magnetic field with an extrapolated value of the critical field of around 18 kOe which can drive T(N) to zero. Electrical resistivity under pressure (<11 GPa) reveals that the magnetic ordering temperature is pushed up dramatically to higher temperatures which is quite interesting if compared with the behavior in isostructural FeAs-based systems containing Eu. Above 7 GPa, the pressure-induced state appears to be ferromagnetic. The results thus reveal interesting changes in the magnetic ordering behavior of this compound with increasing pressure and magnetic fields.     

Effect of magnetic field on Nd0.7Pb0.3MnO3 single crystal

Magnetization and specific heat of Nd_0.7Pb_0.3MnO₃ single crystal are studied at applied magnetic field. Magnetization measurement at 0.3 T shows ferromagnetic phase below 150 K (T_C) and below 20 K displays an antiferromagnetic component. The latter appears to be destroyed at 4.8 T. This anomalous increase below 50 K is probably due to reorientation of Nd moments at high magnetic field. Heat capacity has been measured at 0-10 T at low temperature. The data have been fitted to contributions from free electrons (γ), ferromagnetic spin excitations (β_3/2), lattice and a Schottky-like anomaly related to the rare-earth magnetism of the Nd ions. Fitting yields that β_3/2 term is very small at 6 and 10 T because of introducing paramagnetic component in ferromagnetic phase at applied magnetic field. Peak due to Schottky anomaly is observed to be broadened with application of magnetic field and the magnitude of Schottky gap(Δ_Sch) also increases accordingly.