Itinerant ferromagnetism in the layered crystalsLaCoOX(X=P,As)

Abstract

The electronic and magnetic properties of cobalt-based layered oxypnictides, LaCoOX (X = P, As), are investigated. LaCoOP and LaCoOAs show metallic type conduction with room temperature resistivities of ~2×10 -4 Ω·cm, and the Fermi edge is observed by hard x-ray photoelectron spectroscopy. Ferromagnetic transitions occur at 43 K for LaCoOP and 66 K for LaCoOAs with spontaneous magnetic moments of 0.33 µ B and 0.39 µ B extrapolated to 0 K, respectively. Above the transition temperatures, the magnetic susceptibility exhibits a large temperature dependence. Provided that this temperature dependence follows the Curie-Weiss law, enhanced magnetic moment values of ~2.9 µ B for LaCoOP and ~1.3 µ B for LaCoOAs are obtained. X-ray magnetic circular dichroism (XMCD) is observed at the Co L 2,3 -edge, but not at the other edges. The calculated electronic structure shows a spin polarized ground state with a magnetic moment of 0.52 µ B , ~95% of which is localized on the Co ions. These results indicate that LaCoOX are itinerant ferromagnets and suggest that their magnetic properties are governed by spin fluctuation. PACS

Superconductivity inLaFe1−xCoxAsO

“…5b, inset); for this sample, 55 K < T c < 58 K. This range of T c is slightly lower than that reported earlier [1,43]. Despite the suggestion of a ferromagnetic component in magnetization measurements, there is lack of anomaly in specific heat on several different polycrystalline samples.…”

Superconductivity inNdFe1−xCoxAsO(

“…This is analogous to LaCoAsO, which has a Curie temperature of ϳ60 K and a moment of 0.5 B , 13,22 and consistent with calculations for LaCoAsO that reveal a spin-polarized band structure with a small ordered moment. 22 Our Arrott plots suggest a linear dependence of M 2 on H / M in large fields typical of weak itinerant ferromagnets such as ZrZn 2 but different to the "anomalous" M 4 dependence reported for LaCoAsO. 23 More extensive measurements are needed to investigate this.…”

“…LaCoAsO is an itinerant ferromagnet 13,22 with an anomalous magnetization similar to MnSi and Fe x Co 1−x Si. 23 BaCo 2 As 2 is not ferromagnetic ͑FM͒ but is in close proximity to a FM quantum critical point.…”

Electromagnetic properties and electronic structure of the iron-based layered superconductor LaFePO

“…It is worth noting that the electromagnetic properties of LaOT M P drastically change with the number of 3d electrons, i.e., an antiferromagnetic semiconductor for Mn (3d 5 ) [22], a ferromagnetic metal for Co (3d 7 ) [22], a superconductor for Ni (3d 8 ) [23], and a semiconductor for Zn (3d 10 ) [24]. It should be noted that a family compound, LaOFeAs, exhibits superconductivity at much higher temperatures up to 26 K upon F doping to the oxygen ion sites.…”