Showing papers on "Spin canting published in 1998"

Structural and magnetic properties of ball milled copper ferrite

Abstract: The structural and magnetic evolution in copper ferrite (CuFe2O4) caused by high-energy ball milling are investigated by x-ray diffraction, Mossbauer spectroscopy, and magnetization measurements. Initially, the milling process reduces the average grain size of CuFe2O4 to about 6 nm and induces cation redistribution between A and B sites. These nanometer-sized particles show superparamagnetic relaxation effects at room temperature. It is found that the magnetization is not saturated even with an applied field of 9 T, possibly as the result of spin canting in the partially inverted CuFe2O4. The canted spin configuration is also suggested by the observed reduction in magnetization of particles in the blocked state. Upon increasing the milling time, nanometer-sized CuFe2O4 particles decompose, forming α-Fe2O3 and other phases, causing a further decrease of magnetization. After a milling time of 98 h, α-Fe2O3 is reduced to Fe3O4, and magnetization increases accordingly to the higher saturation magnetization va...

Phase diagram of manganese oxides

Abstract: We study theoretically the phase diagram of perovskite manganites taking into account the double degeneracy of the ${e}_{g}$ orbitals in a ${\mathrm{Mn}}^{3+}$ ion. A rich phase diagram is obtained in the mean-field theory at zero temperature as functions of $x$ (hole concentration) and ${J}_{S}$ (antiferromagnetic interaction between ${t}_{2g}$ spins). The global features of the phase diagram are understood in terms of the superexchange and double-exchange interactions, which strongly depend on the types of occupied ${e}_{g}$ orbitals. The strong electron correlation induces the orbital polarization, which controls the dimension of the conduction band. A sequential change of the spin and orbital structures with doping holes is consistent with the recent experiments. In particular, a metallic $A$-type (layered) antiferromagnetic state is found for $x\ensuremath{\sim}0.5$ with the uniform ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital ordering. In this phase, calculated results suggest two-dimensional conduction and absence of the spin canting, which are observed experimentally. The effects of the Jahn-Teller distortion are also studied.

Spin Canting in γ-Fe 2 O 3 Nanoparticles

Abstract: Dispersions of γ-Fe2O3 particles in a polymer were investigated by Mossbauer spectroscopy with a longitudinal magnetic field of 60 kOe. Spin canting effects as a function of the mean particle size varying from 3 to 10 nm, the interparticle distance, and the temperature are reported.

High-Pressure Synthesis and Magnetic Properties of Layered Double Perovskites Ln2CuMO6 (Ln = La, Pr, Nd, and Sm; M = Sn and Zr)

Abstract: Ln{sub 2}CuSnO{sub 6} (Ln = Pr, Nd, and Sm) and La{sub 2}CuZrO{sub 6} have been stabilized in the same layered double perovskite structure as La{sub 2}CuSnO{sub 6} at high pressures of 6--8 GPa. Their crystal structures and magnetic properties were investigated. Replacement of La{sup 3+} by smaller lanthanide ions and Sn{sup 4+} by larger Zr{sup 4} increased the buckling of the Cu-O-Cu bonds in the CuO{sub 2} layers. In Nd{sub 2}CuSnO{sub 6}, both the Cu and Nd sublattice were found to exhibit weak ferromagnetism owing to spin canting. The magnetization data showed an anomalous transition at 110 K.

Some aspects of the theory of magnets with competing double exchange and superexchange interactions

Abstract: In colossal magnetoresistance materials, ferromagnetic double exchange presumably coexists with a direct nearest-neighbor antiferromagnetic interaction. We construct a single-site mean-field theory that explicitly takes into account the different nature of carrier-mediated ferromagnetism vs Heisenberg-like superexchange. We find, in contrast to previous results in the literature, that the competition between these two exchange interactions leads to ferromagnetic or antiferromagnetic order with incomplete saturation of the magnetization (or sublattice magnetization), rather than spin canting. The associated experimental implications are discussed. {copyright} {ital 1998} {ital The American Physical Society}

Unidirectional anisotropy in ultrathin transition-metal films

Abstract: Unidirectional magnetic anisotropies in low-symmetry magnetic thin films such as cobalt on vicinal copper surfaces are investigated. Possible explanations of the observed uniaxial anisotropies are competing anisotropy (CA) coefficients and Dzyaloshinskii-Moriya (DM) interactions. Unidirectional CA is an interesting mechanism occurring in low-symmetry magnets and involves neither antiferromagnetic exchange nor spin canting. It is visible in the easy-cone regime and decides, for example, whether the preferential magnetization direction points up or down a stepped surface. In the case of $\mathrm{C}\mathrm{o}/\mathrm{C}\mathrm{u}(11n)$ films, however, the anisotropy direction speaks in favor of DM-type interactions.

Structure and magnetic properties of BaCoTiFe10O19 thin films with an easy-axis in-plane orientation

Abstract: BaCoTiFe10O19 hexaferrite thin films with an easy-axis in-plane orientation were prepared by crystallization of amorphous films deposited by rf magnetron sputtering. The structure and magnetic properties were investigated. It is shown that CoTi-doping leads to a reduction of spontaneous magnetization and magnetic moment, which is caused by non-collinear magnetic structure and surface spin canting of small particles. The substitution of CoTi for Fe can adjust coercivity and Curie temperature over a very wide range, while still maintaining the room temperature magnetization. It is found that BaCoTiFe10O19 films exhibit a large squareness of hysteresis loop, Sq = 0.68. Thus, this film is desirable for high-density longitudinal recording systems.