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Spin reorientation has been observed in CoFe 2 O 4 thin single crystalline films epitaxially grown on ͑100͒ MgO substrate upon varying the film thickness. The critical thickness for such a spin-reorientation transition was estimated to be 300 nm. The reorientation is driven by a structural transition in the film from a tetragonal to cubic symmetry. At low thickness, the in-plane tensile stress induces a tetragonal distortion of the lattice that generates a perpendicular anisotropy, large enough to overcome the shape anisotropy and to stabilize the magnetization easy axis out of plane. However, in thicker films, the lattice relaxation toward the cubic structure of the bulk allows the shape anisotropy to force the magnetization to be in plane aligned. The importance of magnetic anisotropy is well recognized in many technical applications such as magnetic and magneto-optic recording. The large interest for high anisotropies is motivated by technological demands such as increasing the magnetic recording density. With large anisotropy, the superparamagnetic limit can be pushed down, and a stable magnetization can be promoted in ultrasmall nanosized magnetic structures, which are needed in advanced media for ultrahigh density recording. Besides the intrinsic anisotropy of the bulk, other sources of anisotropy may be enhanced in artificial structures and contribute to their magnetic properties. Depending on their relative orientations and magnitudes, the involved anisotropies may compete between each other, leading to spin-reorientation phenomena in the system. For example, the broken symmetry at the interfaces in ultrathin films generates a perpendicular anisotropy, which overcomes the shape anisotropy.1 However, increasing the layer thickness reduces the ratio between the surface and the volume atoms, leading to an in-plane alignment of the easy axis.2 In obliquely sputtered metallic thin films, we established the existence of an in-plane reorientation of magnetic anisotropy.3 Depending on the film thickness and due to the shadow effect during the growth, the layer can develop columns or nuclei able to confine the anisotropy parallel or perpendicular to the longitudinal direction ͑projection of the incident beam in the film plane͒.Ferrites cover a large family of oxides, including soft as well as hard magnetic materials. Hard ferrites such as the hexagonal ͑BaFe 12 O 19 ͒ and the spinel ͑CoFe 2 O 4 ͒ are particularly attractive for magnetic and magneto-optic recording applications due to their large magnetocrystalline anisotropy and high chemical stability. Recent studies demonstrated that integrating cobalt ferrite as a pinning layer in the spin valve architecture can strongly enhance the magnetoresistance effect of the sandwiched structure. 4 In epitaxial hexaferrite thin films, the uniaxial magnetocrystalline anisotropy is strong enough to dominate all the other sources of anisotropy and to keep the spin alignment constant regardless the film thickness and the preparation conditions. 5 However, cobalt ferrite rep...

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The crystal structure, magnetic ground state, and the temperature dependent

We report the structural and magnetic properties of polycrystalline ferriferricyanide, Fe͓Fe͑CN͒ 6 ͔ •4H 2 O. The room temperature neutron diffraction pattern of the sample was refined with space group Fm3m by the Rietveld refinement technique. The Mössbauer spectrum of the sample at room temperature reveals the presence of low spin Fe 3+ ͑Fe LS , S =1/2͒ and high spin Fe 3+ ͑Fe HS , S =5/2͒ ions. The compound undergoes a paramagnetic to ferromagnetic phase transition at 17.4 K. Saturation magnetization at 2.3 K corresponds to parallel ordering of Fe HS and Fe LS spin only moments in Fe͓Fe͑CN͒ 6 ͔ •4H 2 O. Neutron diffraction study at 1.5 K shows the ordered site moments of 5.0͑2͒ and 0.8͑2͒ B for Fe HS and Fe LS ions, respectively, in Fe HS ͓Fe LS ͑CN͒ 6 ͔ •4H 2 O. The coercive field of the compound is an order of magnitude higher than that of many other compounds in the Prussian Blue analog family. The observed branching between field-cooled and zero field-cooled magnetization below T C ͑=17.4 K͒ is ascribed due to magnetic domain kinetics under different cooling conditions and the presence of available vacant sites in the lattice for the water molecules.

A crossover of the field-cooled magnetization from positive to negative has been observed below the magnetic ordering temperature (17.9 K) in a multimetal Prussian Blue analogue (PBA), Cu_{0.73}Mn_{0.77}[Fe(CN)_{6}].zH_{2}O. The reverse Monte Carlo (RMC) modeling (using the program RMCPOW) has been used to derive the various scattering contributions (e.g., nuclear diffuse, nuclear Bragg, magnetic diffuse, and magnetic Bragg) from the observed neutron diffraction patterns. The RMC analysis combined with the Rietveld refinement technique show an antiferromagnetic ordering of Mn moments with respect to the Cu as well as the Fe moments. Our study gives the first neutron magnetic structure evidence towards the microscopic understanding of the negative magnetization in the PBAs. This information can be effectively utilized to design suitable PBAs for making multifunctional devices.

The two-step process of transfer followed by breakup is explored by measuring a rather complete set of exclusive data for reaction channels populating states in the ejectile continua of the 7 Li+ 93 Nb system at energies close to the Coulomb barrier. The cross sections for α + α events from one proton pickup were found to be smaller than those for α + d events from one neutron stripping and α + t events from direct breakup of 7 Li. Coupled channels Born approximation and continuum discretized coupled channels calculations describe the data well and support the conclusion that the α + d and α + α events are produced by direct transfer to unbound states of the ejectile.PACS numbers: 25.70. Hi,25.70.Bc,24.10.Eq,25.70.Mn, Exploring the properties of weakly-bound stable/unstable nuclei via transfer reactions is a topic of current interest [1,2] and also a focus of the next generation of high-intensity isotope-separator on-line (ISOL) radioactive ion beam facilities. Due to the low breakup threshold of such nuclei, population of the continuum is probable and consequently a large coupling effect is expected at energies around the Coulomb barrier. This may take place directly through inelastic excitation of the projectile (prompt or resonant breakup) or by nucleon transfer leaving the ejectile in an unbound state (transferbreakup) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The large positive Q-values for the transfer of neutrons from light neutron-rich projectiles to heavy targets also emphasize the role of neutron evaporation following transfer [16,17]. Exclusive measurements are essential to disentangle these reaction channels. Also, complete measurements of different reaction channels as well as theoretical calculations are required to understand the interplay between them. Among the limited exclusive measurements aimed at studying different breakup processes, very few data on absolute cross sections are available for direct breakup [4][5][6][7][8]13], while for transfer-breakup absolute differential cross sections are only available for the neutron transfer channels at energies close to the Coulomb barrier [5,7].Among the processes discussed above, investigation of the two-step reaction mechanism, viz., one nucleon transfer followed by breakup, is of current interest for the weakly-bound stable nuclei 6,7 Li and 9 Be [5, 9-12, 14, 18]. This complex process needs the simultaneous understanding of both the breakup and transfer reactions. In an earlier measurement of the 7 Li+ 65 Cu system [5] it was observed that 1n-stripping leading to 6 Li in its unbound 3 + 1 excited state is more probable than inelastic excitation of 7 Li to its resonant states. In recent measurements with 7 Li [9, 10], the importance of * sanat@barc.gov.in 1p-pickup over the direct breakup of the projectile was highlighted while explaining the suppression of fusion at energies above the Coulomb barrier. Hence, understanding the mechanism of projectile breakup-whether direct or transfer breakup-is crucial while studying the reaction d...

A highly reversible (bipolar) switching of magnetization in a Prussian blue type molecular magnet Cu0.73Mn0.77[Fe(CN)6]⋅zH2O using low magnetic fields is demonstrated. The studied molecular compound also shows both positive and negative magnetocaloric effects below its magnetic ordering temperature. A molecular field theory calculation has also been done to explain the observed temperature dependent magnetization reversal behavior. Possible applications of the magnetic pole reversal phenomenon in magnetoelectronic and magnetocaloric devices such as magnetic memory and magnetic cooling/heating based constant temperature bath have been revealed.