A.R. Rodrigues

Spin-glass and random-field effects in exchange-biased NiFe film on a NiO single-crystal substrate

Magnetization (M) data on a ferromagnetic/antiferromagnetic (FM/AF) sample made of a permalloy thin film sputtered on a thick NiO single-crystal substrate reveal remarkable irreversibilities. The field, temperature (T), and time dependencies of M were measured after the sample was cooled in zero-field or in the presence of a field, keeping T below the Neel temperature, with the field applied in the plane, either perpendicular or parallel to the anisotropy direction. While the behavior observed in the perpendicular configuration is characteristic of spin glasses, in the parallel configuration it exhibits features of random-field systems. The observed metastabilities and thermal history dependencies are shown to result from frustrations and randomness due to the interface roughness.

Giant magnetoimpedance effect in a thin-film multilayer meander-like sensor

A meander-like magnetic sensing element based on the giant magnetoimpedance (GMI) effect was prepared by using optical lithography and sputtering deposition techniques. The structure of the sensing element consists of layers of Permalloy (Py = Ni81Fe19), titanium (Ti), and copper (Cu) with composition [Py(100 nm)/Ti(6 nm)]4/Cu(400 nm)/[Py(100 nm)/Ti(6 nm)]4. The GMI was investigated at room temperature under applied magnetic fields (H) varying in the range of ±4.0 kOe in both longitudinal and transversal geometries. The amplitude Iac and frequency f of the ac electrical current were varied in the range of 0.35–6.50 mA and 0.1–20 MHz, respectively. The overall dc electrical resistance of the sensing element was found to be 45.6 Ω. The sensing element yielded a GMI of 53.5% for H ≃ 5.0 Oe and f = 7.0 MHz, and the corresponding maximum average sensitivity of about 5 Ω/Oe. The sensing element was used for measuring the local Earth magnetic field ( H l o c a l = 0.26 ± 0.03 Oe) yielding a value close to the on...

The osmotic pressure of saturated3He−4He mixtures, polarized by dilution

Liquid3He has been cooled (T=10−15 mK)and polarized by means of a4He circulating dilution refrigerator. The polarization becomes stationary at 0.15, 7 times the equilibrium polarization in our external field of 7 T. Based on the behavior of the refrigerator as a polarizer, we claim that the molar susceptibilities of coexisting concentrated and dilute3He are equal at a pressure of 2.6±0.04 bar. We have measured the osmotic pressure in the dilute phase as a function of the polarization of the concentrated phase up to 0.15. Applying the Clausius-Clapeyron equation for the field dependence of the osmotic pressure gives the susceptibility of the saturated dilute phase. Our results agree with NMR experiments on the dilute phase by Ahonen et al. after multiplying their results by 0.9.

Low temperature magnetotransport properties of La0.55Ho0.15Sr0.3MnO3

Magnetotransport data measured in thin films of La 0.55 Ho 0.15 Sr 0.3 MnO 3 down to very low temperatures (0.25 K) are reported. The samples presented colossal magnetoresistance with a T C close to 200 K. A minimum in the resistance vs. T curve and a drop in the ZFC magnetization were also observed. It was also found a T-dependent relaxation effect after the magnetic field was either applied or removed. These results can be understood within the framework where electronic scattering occurs across magnetic domain walls in a reentrant spin-glassy-like phase.

Magnetic Properties of Organic Acid-Doped Polyaniline

Magnetization and magnetic susceptibility of pellets of polyaniline basic- EB and acid doped-ES(HCOOH) and ES(HCl) were measured as a function of the temperature and magnetic field. Few but large magnetic moments are responsible for the magnetism in these materials.