J. Hamrle

Improvement of structural, electronic, and magnetic properties of Co2MnSi thin films by He+ irradiation

The influence of 30 keV He+ ion irradiation on structural, electronic, and magnetic properties of Co2MnSi thin films with a partial B2 order was investigated. It was found that room temperature irradiation with light ions can improve the local chemical order. This provokes changes of the electronic structure and element-specific magnetization toward the bulk properties of a well-ordered Co2MnSi Heusler compound.

Theory of the radiation of dipoles placed within a multilayer system

A rigorous theory of radiation from dipoles embedded inside an arbitrary multilayer system is presented. In particular, we derive explicit expressions for the angular distribution of the electromagnetic field and the intensity radiated by the dipole into the surrounding media. Under the assumptions of mutual incoherence of the dipole radiation the calculations are extended to a layer of radiating dipoles. Special configurations corresponding to (i) a single dipole near a dielectric interface, (ii) a dipole layer surrounded by semi-infinite dielectric media, and (iii) a dipole layer placed on top of a waveguide layer are discussed in detail. This theoretical analysis has important consequences for the optimization of optical chemical sensors and biosensors that are based on fluorescence emission.

Spin-dependent boundary resistance in the lateral spin-valve structure

We report the detection of clear spin-valve signal without any spurious magnetoresistive signal in a lateral spin-valve structure consisting of Cu∕Ni−Fe ohmic junction using local current injection. The obtained spin-valve signal is much larger than that of the nonlocal spin-valve configuration because of the efficient spin accumulation. The local current injection experiments with different probe configurations proved that the spin-valve signal is caused by the spin-dependent boundary resistance at the interface between the ferromagnetic voltage probe and the spin-polarized nonmagnetic wire.

Huge quadratic magneto-optical Kerr effect and magnetization reversal in the Co2FeSi Heusler compound

Co2FeSi(1 0 0) films with L21 structure deposited onto MgO(1 0 0) were studied using both the longitudinal and quadratic (QMOKE) magneto-optical Kerr effect. The films exhibit a huge QMOKE signal with a maximum contribution of up to 30 mdeg, which is the largest QMOKE signal in reflection that has been measured thus far. This large value is a fingerprint of an exceptionally large spin–orbit coupling of second or higher order. The Co2FeSi(1 0 0) films exhibit a rather large coercivity of 350 Oe and 70 Oe for film thicknesses of 22 nm and 98 nm, respectively. Despite the fact that the films are epitaxial, they do not provide an angular dependence of the anisotropy and the remanence in excess of 1% and 2%, respectively.

Transport and optical properties of the gapless Heusler compound PtYSb

This work presents a systematic study on the optical and transport properties of the Heusler compound PtYSb. The optical properties were investigated in a wide spectral range from 10 meV to 6.5 eV and compared to ab-initio calculations. For photon energies below 2.5 eV, the optical absorption increases linearly with photon energy. This is related with the conical shape of the electronic structure in the vicinity of the Fermi energy. The optical spectra reveal a maximum band gap of about 60 meV. Furthermore, the temperature dependence of thermal conductivity, electrical resistivity, Seebeck coefficient and Hall mobility were investigated. PtYSb exhibits very good thermoelectric properties with a high figure of merit ZT of 0.2 and a Hall mobility μh of 300 cm2/Vs at 350 K, which is the highest value obtained for Heusler compounds up to now. The carrier concentration ranges from 5 × 1018 at low temperature to 1019 cm−3 at 400 K.

Influence of the L21 ordering degree on the magnetic properties of Co2MnSi Heusler films

We report on the influence of the improved L21 ordering degree on the magnetic properties of Co2MnSi Heusler films. Different fractions of the L21 phase are obtained by different postgrowth annealing temperatures ranging from 350 °C to 500 °C. Room temperature magneto-optical Kerr effect measurements reveal an increase of the coercivity at an intermediate annealing temperature of 425 °C. This is probably a result of an increasing number of pinning centers on the one hand and a drop of the cubic anisotropy constant K1 by a factor of 10 on the other for an increasing amount of the L21 phase. Furthermore, Brillouin light scattering studies show that the improvement of the L21 order in the Co2MnSi films is correlated with a decrease of the saturation magnetization by about 7%. The exchange stiffness constant of Co2MnSi, however, increases by about 8% when the L21 order is improved.

Determination of exchange constants of Heusler compounds by Brillouin light scattering spectroscopy: application to Co2MnSi

Brillouin light scattering spectroscopy from so-called standing spin waves in thin magnetic films is often used to determine the magnetic exchange constant. The data analysis of the experimentally determined spin-wave modes requires an unambiguous assignment to the correct spin wave mode orders. Often additional investigations are needed to guarantee correct assignment. This is particularly important in the case of Heusler compounds where values of the exchange constant vary substantially between different compounds. As a showcase, we report on the determination of the exchange constant (exchange stiffness constant) in Co

Determination of magnetic vortex chirality using lateral spin-valve geometry

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Suppression of spin accumulation in nonmagnet due to ferromagnetic ohmic contact

MnSi, which is found to be

Current distribution inside Py/Cu lateral spin-valve devices

A=2.35\pm0.1