In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

Author(s): Ahn, KH; Wu, XW; Liu, K; Chien, CL | Abstract: The effect of Fe doping (l20%) on the Mn site in the ferromagnetic ((Formula presented)) and the antiferromagnetic ((Formula presented)) phases of (Formula presented) has been studied. The same ionic radii of (Formula presented) and (Formula presented) cause no structure change in either series, yet conduction and ferromagnetism have been consistently suppressed by Fe doping. Colossal magnetoresistance has been shifted to lower temperatures, and in some cases enhanced by Fe doping. Doping with Fe bypasses the usually dominant lattice effects, but depopulates the hopping electrons and thus weakens the double exchange. © 1996 The American Physical Society.

Magnetic properties and colossal magnetoresistance of LaÑCaÖMnO3 materials doped with Fe

The authors investigate the properties of 378 half-Heusler compounds using density functional theory with the goal of identifying promising candidates for spintronic applications, e.g. half-metals. Although DFT has often been applied to the search for half-metals, this study may be the most comprehensive attempt to identify which of the compounds predicted by DFT to be half-metals are likely to be fabricated. The calculated formation energy of each of the 378 potential half Heuslers was compared to that of all competing phases and combination of phases in the Open Quantum Materials Database. Those semiconductors, half-metals, and near half-metals within an empirically determined 0.1 eV/atom hull distance margin for neglected effects were deemed of interest for further experimental investigation.

Computational investigation of half-Heusler compounds for spintronics applications

The phenomenon of negative magnetization and its implications

Magnetic behaviour of the orthochromite La0.5Gd0.5CrO3

Literature reports on bulk sample of the ferrite Ni 0 . 5 Co 0 . 5 Fe 2 O 4 confirm a complete inverse spinet structure. On site occupancy and magnetic anisotropy on nano-particle samples of the titled ferrite prepared usingtwo different routes - a wet chemical co-precipitation process and sol-gel method have been studied. Estimated average particle sizes of the two samples (referred to as NCWET and NCSOL) are ∼75A and ∼190A respectively. Small angle neutron scattering measurements made on the fluid sample comprising the sample prepared by wet chemical process gives median size ∼77A with standard deviation σ = 0.60. Mosshauer studies at 300K show that the two ferrite samples maintain inverse spine structure even in nanocrystalline state. Magnetization and Mosshmier measurements show that part of the sample in both the cases is in superparainagnetic state. Magnetic anisotropy is larger in the nano-particle state and surface spin disorder also contributes to this.

http://nopr.niscair.res.in/bitstream/123456789/9593/1/IJPAP%2042%285%29%20366-370.pdf

Magnetic behaviour of nanoparticles of ni0.5co0.5fe2o4 prepared using two different routes

Magnetic behaviour of alloys in the series (Fe1−xCox)2P

Re-entrant spin glass like behaviour of (Fe0.90Cr0.05Ni0.05)2P

DC magnetization measurements are reported in the temperature range 20–100 K on a poly-disperse nano-particle sample of the spinel ferrite Fe2.9Zn0.1O4 with a log-normal size distribution of median diameter 43.6 A and standard deviation 0.58. Outside a core of ordered spins, moments in surface layer are disordered. Results also show some similarities with conventional spin glasses. Blocking temperature exhibits a near linear variation with two-third power of the applied magnetic field and magnetizationM evolves nearly linearly with logarithm of timet. Magnetic anisotropy has been estimated by analysing theM-logt curve. Anisotropy values show a large increase over that of bulk particle samples. Major contribution to this enhancement comes from the disordered surface spins.

Bipin K. Srivastava

Papers

Magnetic behaviour of the orthochromite La0.5Gd0.5CrO3

Magnetic behaviour of nanoparticles of ni0.5co0.5fe2o4 prepared using two different routes

Magnetic behaviour of alloys in the series (Fe1−xCox)2P

Re-entrant spin glass like behaviour of (Fe0.90Cr0.05Ni0.05)2P

Magnetic behaviour of nano-particles of Fe2.9Zn0.1O4