Néel temperature

About: Néel temperature is a research topic. Over the lifetime, 6407 publications have been published within this topic receiving 97870 citations. The topic is also known as: Néel point.

Sol−Gel Synthesis of KVII[CrIII(CN)6]·2H2O: A Crystalline Molecule-Based Magnet with a Magnetic Ordering Temperature above 100 °C

Abstract: Recently, there has been much interest in the synthesis of molecule-based magnets, which are magnets whose solid-state structures consist of arrays of molecular units. 1,2 Such solids do not at present have real-world uses, in part because none of them possesses a key characteristic: for most commercial applications, a magnet must retain its magnetism well above room temperature. Of the four molecule-based magnets that remain magnetic at room temperature, one decomposes at 350 K, 3 and three demagnetize near 315 K. 4,5 All four of these solids are amorphous, and their solid state structures are unknown, although the latter three probably adopt a structure like that of the pigment Prussian blue. We now describe the use of sol -gel methods to synthesize several crystalline molecule-based magnets with the Prussian blue structure. The gelation process appears to be important to the growth of the crystalline phase. Most notable among the current results is the discovery of a molecule-based magnet, KV II[CrIII (CN)6]‚2H2O, with the unprecedented magnetic ordering temperature of 376 K (103°C). The four known molecule-based magnets that keep their magnetism at room temperature are listed below, along with the temperatures at which the magnetism is lost:

High-Temperature Molecular Magnets Based on Cyanovanadate Building Blocks: Spontaneous Magnetization at 230 K

Abstract: The molecular-based magnetic materials Cs 2 Mn || [V || (CN) 6 ] (1) and (Et 4 N) 0.5 Mn l.25 - [V(CN) 5 ]·2H 2 O ( 2 ) (where Et is ethyl) were prepared by the addition of manganese(II) triflate to aqueous solutions of the hexacyanovanadate(II) ion at 0°C. Whereas 1 crystallizes in a face-centered cubic lattice, 2 crystallizes in a noncubic space group. The cesium salt (1) has features characteristic of a three-dimensional ferrimagnet with a Neel transition at 125 kelvin. The tetraethylammonium salt (2) also behaves as a three-dimensional ferrimagnet with a Neel temperature of 230 kelvin; only two other molecular magnets have higher magnetic ordering temperatures. Saturation magnetization measurements indicate that in both compounds the V II and high-spin Mn II centers are antiferromagnetically coupled. Both 1 and 2 exhibit hysteresis loops characteristic of soft magnets below their magnetic phase-transition temperatures. The high magnetic ordering temperatures of these cyano-bridged solids confirm that the incorporation of early transition elements into the lattice promotes stronger magnetic coupling by enhancing the backbonding into the cyanide π* orbitals.

Onset of antiferromagnetism in heavy-fermion metals

Abstract: There are two main theoretical descriptions of antiferromagnets. The first arises from atomic physics, which predicts that atoms with unpaired electrons develop magnetic moments. In a solid, the coupling between moments on nearby ions then yields antiferromagnetic order at low temperatures1. The second description, based on the physics of electron fluids or ‘Fermi liquids’, states that Coulomb interactions can drive the fluid to adopt a more stable configuration by developing a spin density wave2,3. It is at present unknown which view is appropriate at a ‘quantum critical point’, where the antiferromagnetic transition temperature vanishes4,5,6,7. Here we report neutron scattering and bulk magnetometry measurements of the metal CeCu6-xAux, which allow us to discriminate between the two models. We find evidence for an atomically local contribution to the magnetic correlations which develops at the critical gold concentration (xc = 0.1 ), corresponding to a magnetic ordering temperature of zero. This contribution implies that a Fermi-liquid-destroying spin-localizing transition, unanticipated from the spin density wave description, coincides with the antiferromagnetic quantum critical point.

Robust isothermal electric control of exchange bias at room temperature

Abstract: Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with high-speed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr(2)O(3) has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr(2)O(3) single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Neel temperature.

Coupling between the ferroelectric and antiferromagnetic orders in YMnO 3

Abstract: Anomalies in the dielectric constant and loss tangent have been observed in the ferroelectromagnet YMnO{sub 3} near its N{acute e}el temperature of {approximately}80 K and below its ferroelectric Curie temperature of {approximately}914 K. These anomalies are indicative of coupling between the ferroelectric and antiferromagnetic orders in this compound. A small but distinct magnetoelectric effect and a magnetoresistive effect up to {approximately}15{percent} were also detected in a magnetic field at 5 T. The results will be contrasted with previous theoretical predictions. {copyright} {ital 1997} {ital The American Physical Society}