A negative isotropic magnetoresistance effect more than three orders of magnitude larger than the typical giant magnetoresistance of some superlattice films has been observed in thin oxide films of perovskite-like La0.67Ca0.33MnOx. Epitaxial films that are grown on LaAIO3 substrates by laser ablation and suitably heat treated exhibit magnetoresistance values as high as 127,000 percent near 77 kelvin and ∼1300 percent near room temperature. Such a phenomenon could be useful for various magnetic and electric device applications if the observed effects of material processing are optimized. Possible mechanisms for the observed effect are discussed.

http://science.sciencemag.org/content/sci/264/5157/413.full.pdf

Thousandfold Change in Resistivity in Magnetoresistive La-Ca-Mn-O Films

Multiferroic magnetoelectrics are materials that are both ferromagnetic and ferroelectric in the same phase. As a result, they have a spontaneous magnetization that can be switched by an applied magnetic field, a spontaneous polarization that can be switched by an applied electric field, and often some coupling between the two. Very few exist in nature or have been synthesized in the laboratory. In this paper, we explore the fundamental physics behind the scarcity of ferromagnetic ferroelectric coexistence. In addition, we examine the properties of some known magnetically ordered ferroelectric materials. We find that, in general, the transition metal d electrons, which are essential for magnetism, reduce the tendency for off-center ferroelectric distortion. Consequently, an additional electronic or structural driving force must be present for ferromagnetism and ferroelectricity to occur simultaneously.

Why Are There so Few Magnetic Ferroelectrics

http://sces.phys.utk.edu/mostcited/mc1_1114.pdf

Colossal Magnetoresistant Materials: The Key Role of Phase Separation

Publisher Summary This review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation. Although the number of references cited in our review show that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures. In the past, systems containing an element in two different states of oxidation have gone by various names, the terms “mixed valence,” nonintegral valence,” “mixed oxidation,” “oscillating valency,” and “controlled valency” being used interchangeably. Actually, none of these is completely accurate or all-embracing, but in our hope to avoid the introduction of yet another definition, we have somewhat arbitrarily adopted the phrase “mixed valence” for the description of these systems. The concept of resonance among various valence bond structures is one of the cornerstones of modern organic chemistry.

Mixed Valence Chemistry-A Survey and Classification

A technique for reduction of the Dirac equation, which initially omits the spin-orbit interaction (thus keeping spin as a good quantum number), but retains all other relativistic kinematic effects such as mass-velocity, Darwin, and higher order terms is presented. The spin-orbit interaction can be included as a perturbation once the 'relativistic' spin-polarised bands and wavefunctions have been obtained. The technique is used together with the local spin density approximation for exchange and correlation to calculate the self-consistent charge and spin density of a neutral Gd atom. The calculated magnetic form factor agrees extremely well with experiment. Comparison with a paramagnetic RAPW calculation shows the procedure should be accurate and fast for general band structure determinations.

https://iopscience.iop.org/article/10.1088/0022-3719/10/16/019/pdf

A technique for relativistic spin-polarised calculations

Alloys of the heavy rare earth metals with La have been studied by neutron‐diffraction methods. For alloys with 15 at.% or less of La the alloys have the simple hcp structure. The influence of La on the magnetic structures of the metals is such as to enhance the stability of a ferromagnetic configuration relative to an oscillatory one. The transition temperature is lower and the initial turn angle (when it exists) smaller in a lanthanum alloy than in the corresponding yttrium alloy. In the lanthanum‐rich region, the system La–Tb has been most extensively studied with five compositions ranging from Tb0.10La0.90 to Tb0.75La0.25 having been investigated. Of these, the compositions Tb0.20La0.80, Tb0.40La0.60 and Tb0.50La0.50 formed a single phase alloy with the double hexagonal lanthanum structure (dhcp). The 4.2°K diffraction patterns of these three alloys exhibited a number of broad diffraction maxima rather similar to those found for Nd in the antiferromagnetic region. Neel temperatures of approximately 50°, 68°, and 75°K, respectively, were estimated for the three specimens. The specimen Tb0.75La0.25 exhibited lines from the hcp and dhcp structures as well as of a third phase which is probably the δ phase. In the Tb0.10La0.90 alloy both a dhcp and fcc phase were observed at room temperature; the low‐temperature pattern exhibited magnetic reflections characteristic of the dhcp alloys. The La‐rich Tb alloys thus are antiferromagnetic, rather than ferromagnetic as had been proposed previously.

Magnetic Properties of Rare Earth‐Lanthanum Alloys

Search for Antiferromagnetism in the Silicides V 3 Si, Cr 3 Si, and Mo 3 Si

The National Center for Small-Angle Scattering Research is a user-dedicated facility supported by the National Science Foundation and the Department of Energy under an interagency agreement. The two main facilities available to users are the NSF constructed 30-m small-angle neutron scattering instrument (SANS) and the 10-m DOE constructed small-angle x-ray scattering camera (SAXS). Test measurements carried out on ATPase in H2O and in D2O buffer indicate that the SANS facility is capable of providing meaningful data on a wide variety of biological systems. Details of work carried out on the instrument by Uberbacher, Olins, and Bunick, on the binding of HMG proteins to nucleosomes, are presented in a separate poster. (Research sponsored by the National Science Foundation under interagency agreement No. 40-637-77 under Union Carbide Corporation contract W-7405-ENG-26 with the U.S. Department of Energy.)

The National Center for Small-Angle Scattering Research

The Coherent Neutron Scattering Cross Sections of Nickel and Its Isotopes

A brief summary is given of recent neutron diffraction investigations at the Oak Ridge National Laboratory on rare-earth metals and nntermetallic compounds. (auth)

W. C. Koehler

Papers

Magnetic Properties of Rare Earth‐Lanthanum Alloys

Search for Antiferromagnetism in the Silicides V 3 Si, Cr 3 Si, and Mo 3 Si

The National Center for Small-Angle Scattering Research

The Coherent Neutron Scattering Cross Sections of Nickel and Its Isotopes

Recent magnetic neutron scattering investigations at oak ridge national laboratory