We have grown thin films of the Heusler compound Co2FeSi by RF magnetron sputtering. On (100)-oriented MgO substrates we find fully epitaxial (100)-oriented and L21 ordered growth. On Al2O3 (1120) substrates, the film growth is (110)-oriented, and several in-plane epitaxial domains are observed. The temperature dependence of the electrical resistivity shows a power law with an exponent of 7/2 at low temperatures. Investigation of the bulk magnetic properties reveals an extrapolated saturation magnetization of 5.0 µB/fu at 0 K. The films on Al2O3 show an in-plane uniaxial anisotropy, while the epitaxial films are magnetically isotropic in the plane. Measurements of the X-ray magnetic circular dichroism of the films allowed us to determine element specific magnetic moments. Finally we have measured the spin polarization at the surface region by spinresolved near-threshold photoemission and found it strongly reduced in contrast to the expected bulk value of 100%. Possible reasons for the reduced magnetization are discussed.

Strained coherent film growth is commonly either limited to ultrathin films or low strains. Here, we present an approach to achieve high strains in thicker films, by using materials with inherent structural instabilities. As an example, 50 nm thick epitaxial films of the Fe70Pd30 magnetic shape memory alloy are examined. Strained coherent growth on various substrates allows us to adjust the tetragonal distortion from c/a{bct}=1.09 to 1.39, covering most of the Bain transformation path from fcc to bcc crystal structure. Magnetometry and x-ray circular dichroism measurements show that the Curie temperature, orbital magnetic moment, and magnetocrystalline anisotropy change over broad ranges.

We investigated element-specific magnetic moments and the spin-resolved unoccupied density of states (DOS) of polycrystalline Co2TiZ (Z=Si, Ge, Sn, Sb), Co2MnxTi1−xSi and Co2MnGa1−xGex Heusler alloys using circular dichroism in x-ray absorption spectroscopy (XMCD). We find a small (<0.03μB) Ti moment oriented antiparallel and a large (>3μB) Mn moment oriented parallel to the Co moment of approximately 1μB per atom in the investigated compounds. Orbital magnetic moments are increased for quaternary compounds compared to the corresponding ternary compounds with x=0 or x=1. The unoccupied spin-resolved partial DOS at the Co atom was extracted from the XMCD data. In the case of Co2TiSi, Co2TiGe, and Co2TiSn, the Co minority DOS reveals a maximum at 0.5 eV above EF and very low values at EF in agreement with the expectation for half-metallic ferromagnetism. In contrast, Co2TiSb shows a large minority DOS at the Fermi energy like a normal metal. A substitution of Ti by Mn in Co2TiSi shifts the minority DOS maximum from 0.5 to 0.9 eV with respect to the Fermi energy. For the series Co2MnGa1−xGex we observe a gradual shift of the minority DOS maximum from 0.7 eV for x=1 to 1.0 eV for x=0, indicating half-metallic ferromagnetism for the whole series. Our results, revealing the distribution of magnetic moments and the relative position of the Fermi energy as a function of the number of valence electrons, confirm the predicted possibility of tailoring the minority band gap using substitutional quaternary Heusler compounds. The results maybe of general importance for the understanding of the electronic structures in complex intermetallic compounds

We investigate the martensitic transition of single crystalline Ni 2 MnGa͑110͒ /Al 2 O 3 ͑1120͒ and Ni 2 MnGa͑100͒ /MgO͑100͒ films using magnetometry, x-ray diffraction, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism. The martensitic transition from the cubic austenite phase to the low symmetry martensite phase depends strongly on the chosen substrate. For ͑110͒ oriented films on Al 2 O 3 , the martensitic phase is significantly more stable than for the ͑100͒ oriented films on MgO. A remarkable change of the Ni x-ray absorption spectra occurs at the transition, indicating specific changes of the electronic structure. The observed changes are in agreement with theoretical predictions. The orbital to spin momentum ratio of the Ni moment increases significantly on entering the martensite state, thus explaining the macroscopic increase of magnetic anisotropy.

In this work, the theoretical and experimental investigations of Co 2 TiZ (Z = Si, Ge or Sn) compounds are reported. Half-metallic ferromagnetism is predicted for all three compounds with only two bands crossing the Fermi energy in the majority channel. The magnetic moments fulfil the Slater-Pauling rule and the Curie temperatures are well above room temperature. All compounds show a metallic-like resistivity for low temperatures up to their Curie temperature, above the resistivity changes to semiconducting-like behaviour. A large negative magnetoresistance (MR) of 55 per cent is observed for Co 2 TiSn at room temperature in an applied magnetic field of m 0 H = 4T , which is comparable to the large negative MRs of the manganites. The Seebeck coefficients are negative for all three compounds and reach their maximum values at their respective Curie temperatures and stay almost constant up to 950 K. The highest value achieved is −52 mVK −1 for Co 2 TiSn, which is large for a metal. The combination of half-metallicity and the constant large Seebeck coefficient over a wide temperature range makes these compounds interesting materials for thermoelectric applications and further spincaloric investigations.