Search

Magnetic systems exhibiting spin-canted states have garnered much attention recently for their promising rich exotic properties driven by the real-space spin textures and competing magnetic orders. In this study, we present the structural and magnetic properties of hexagonal 60 nm MnPtGa epitaxial thin films grown by magnetron sputtering on Al2O3(0001) single-crystalline substrates. The MnPtGa film crystallizes in the centrosymmetric P63/ mmc (No. 194) space group, showing perpendicular magnetic anisotropy along the c-axis, with a Curie temperature TC = 263 K. In addition, the MnPtGa film undergoes a spin reorientation transition at Tsr = 160 K. We investigated the MnPtGa magnetic ground states using single-crystal neutron diffraction. A structurally forbidden (001) magnetic Bragg reflection emerges below Tsr, indicating the existence of a spin-canted state, where the magnetic moments align ferromagnetically perpendicular to the basal plane, and a non-zero in-plane component exhibits an antiferromagnetic ordering along the c-axis. At 2 K, the refined magnetic moments of Mn are μz = 4.2(4) μB and μx = 1.5(3) μB, projected onto the c-axis and basal plane, respectively. Hence, we determined a 20° Mn spin canting angle off from the c-axis.

We report the observation of room temperature spin Seebeck effect (SSE) in a weak ferromagnetic normal spinel Zinc Ferrite (ZFO). Despite the weak ferromagnetic behavior, the measurements of the SSE in ZFO show a thermoelectric voltage response comparable with the reported values for other ferromagnetic materials. Our results suggest that SSE might possibly originate from the surface magnetization of the ZFO.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. Magnetic silica-aerogel composites have been synthesized by dispersing hard magnetic Nd2Fe14B particles in a sol during a fast sol-gel process and subsequently supercritically drying the resulting gels. The composites are found to retain most of the outstanding properties of their constituents: the large coercivity and moderate remanence of the magnetic powders and the transparency and low density of silica aerogels. Moreover, aerogels synthesized in the presence of a magnetic field exhibit the alignment of the particles, forming needle-like structures along the direction of the applied magnetic field, which results in optical and magnetic anisotropies. Due to their unique combination of properties, these types of materials may be appealing for magneto-optics and magnetic actuator applications.

We show that the polycrystalline perovskite antiferromagnet Pr0.5Sr0.5MnO3 exhibits a giant anisotropic magnetostriction (λt=1.5×10−3 at T=25 K and H=14.2 T) contrary to much smaller λt (

The composition dependence of magnetic and structural transformations, as well as the temperature and composition dependence of the magnetocrystalline anisotropy, were studied in the martensitic Ni2+xMn1+yGa1+z (x+y+z=0) Heusler alloys. Moving away from the stoichiometric composition, a slight variation, a large reduction, and a marked enhancement, were, respectively, observed for the Curie temperature, the magnetic anisotropy, and the structural (martensitic–austenitic) transformation temperatures.

Large low-field magnetoresistance (LFMR) together with high Curie temperatures (TC) are requirements for some applications in magnetoelectronics. In order to optimize both parameters, we have investigated double perovskites (Ba0.8Sr0.2)2−xLaxFeMoO6 (0⩽x⩽0.4). High-temperature neutron diffraction measurements indicate a strong increase in TC with La doping (from ≈345 K for x=0 to ≈405 K for x=0.4). The LFMR is very large for x=0 (at 10 KOe≈27% at 10 K and ≈7% at 290 K) and decreases with La doping. This decrease cannot be attributed to a substantial enhancement of Fe/Mo antisite disorder, which is small as tracked by means of x-ray and high-resolution neutron diffraction, but to grain boundaries modifications.

3 páginas, 3 figuras.-- et al., We present a detailed study on the magnetization under high magnetic fields of Tb5Si2Ge2 and Gd5Si2Ge2 compounds. From the Arrott plot construction (A. Arrott, Phys. Rev. 108, 1394 (1957)), we were able to estimate the TC of each structure (M and O(I)) experimentally and found that the TC of the O(I) phase can be directly obtained by extrapolating the TC curve of this phase in the respective phase diagram. Using a physical model based on free energy considerations, one explains the (de)coupling of the magnetic and structural transitions in R5(SixGe1−x)4 (R = Tb, Gd) compounds., Work partially supported by the projects FEDER/POCTI No. 155/94 and PTDC/CTM/NAN/115125/2009, from Fundacaçö para a Ciência e a Tecnologia (FCT), Portugal. A.M.P. and J.S.A. thank FCT for the Grant Nos. SFRH/BPD/63150/ 2009 and SFRH/BPD/63942/2009. C.M. acknowledges the support of the Fundacin ARAID. The financial support of the Spanish MEC (MAT2008-06567-C02) and DGA (Grant No. E26) is acknowledged. Part of this was supported by Euro- MagNET under the EU Contract No. 228043.

The magnetocaloric effect has been investigated in a series of the R5(SixGe1−x)4 pseudobinary alloys with R=Tb and x=0.0, 0.5, and 1.0. In Tb5Si4 and Tb5Ge4, a maximum magnetic entropy change of 9.8 and 3.7 J/kg K, respectively, has been found at their ordering temperatures for a magnetic field change of 50 kOe. In the case of Tb5Ge4, we have observed the existence of a previously unreported magnetic transition below the Neel temperature. Tb5(Si0.5Ge0.5)4 has been successfully synthesized, and a large entropy change of 21.8 J/kg K (ΔH=50 kOe) is achieved at a first-order para- to ferromagnetic transition, TC≅105 K. This study demonstrates that Tb5(SixGe1−x)4 alloys are good candidates for magnetic refrigeration and that very exciting phenomenology in these systems awaits further investigation.

We report the effect of hydrostatic pressure up to 8 kbar on magnetoelastic, magnetic, and transport properties in the temperature range 10–300 K. An increase of Curie temperature Tc with pressure ΔTc/Δp=2.6 K/kbar was determined from ac susceptibility measurements. The anomalies in resistivity and magnetovolume effects are significantly suppressed by pressure but the temperatures of these anomalies increased with pressure with the same slope as Tc. These results indicate that impurity state of yttrium rather than lattice parameter reduction is responsible for the large increase in the magnetoresistance observed in the doped compound.

The magnetoresistance of the FeRh alloy has been measured in the temperature range 200–300 K using high pulsed magnetic fields up to 36 T. This compound shows a first‐order magnetic transition from the antiferromagnetic (AF) low‐temperature state to the ferromagnetic (F) high‐temperature state at TAF–F=405 K. The F state is very close in energy to the AF state and can be reached by applying a magnetic field. The measurements made within the AF state show that the AF–F transition is accompanied by a giant magnetoresistance effect (ΔR/R≊50%).

We have measured the Hall effect and the magnetoresistance of epitaxial Fe3O4 thin films grown on MgO (001) in magnetic fields up to 30 T. Using such high fields, it is possible to magnetically saturate films thicker than 40 nm, providing access to intrinsic conduction properties. We find an effective electron density corresponding to 1 electron per f.u. A smaller value is obtained for thinner films, caused by the increasing density of antiphase boundaries defects. The magnetoresistance is not saturating at 30 T, showing linear dependence at high fields, and peaks at the Verwey transition.

Spin and orbital magnetic moments of Re in AA'FeReO6 double perovskites (A,A' = Ba, Sr, Ca) have been directly probed employing XMCD spectroscopy at the Re L2,3-edges. A considerable orbital magnetic moment is observed in all the studied compounds despite octahedral coordination. Relative orbital to spin contribution per Re atom rises with lattice distortion from mL/mS = -0.28 to -0.34 for AA'=Ba2FeReO6 and Ca2FeReO6, respectively. A preliminary XMCD measurements at the Fe L2,3-edges reveals also a significant orbital moment of iron in Ca2FeReO6. The relation of the results to the magnetic properties of the compounds is discussed.