钴钌氧化物中的反铁磁性、自旋玻璃态、H-T相图及逆磁热效应

Antiferromagnetism, spin-glass state, H-T phase diagram, and inverse magnetocaloric effect in CoRuO.

作者信息

Ghosh Sayandeep, Joshi Deep Chandra, Pramanik Prativa, Jena Suchit K, Pittala Suresh, Sarkar Tapati, Seehra Mohindar S, Thota Subhash

机构信息

Department of Physics, Indian Institute of Technology, Guwahati-781039, Assam, India.

Department of Materials Science and Engineering, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden.

出版信息

J Phys Condens Matter. 2020 Sep 8;32(48). doi: 10.1088/1361-648X/aba6a6.

DOI:10.1088/1361-648X/aba6a6

PMID:32903218

Abstract

Static and dynamic magnetic properties of normal spinel CoRuO= (Co)A[Co3+Ru3+]BO4are reported based on our investigations of the temperature (), magnetic field () and frequency () dependence of the ac-magnetic susceptibilities and dc-magnetization () covering the temperature range= 2 K-400 K and H up to 90 kOe. These investigations show that CoRuOexhibits an antiferromagnetic (AFM) transition at∼ 15.2 K, along with a spin-glass state at slightly lower temperature () near 14.2 K. It is argued thatis mainly governed by the ordering of the spins of Coions occupying the-site, whereas the exchange interaction between the Coions on the-site and randomly distributed Ruon the-site triggers the spin-glass phase, Coions on the-site being in the low-spin non-magnetic state. Analysis of measurements of(,) for, analysis of the paramagnetic susceptibility () vs.data are fit to the modified Curie-Weiss law,=+/(+), with= 0.0015 emu molOeyielding= 53 K and= 2.16 emu-K molOe, the later yielding an effective magnetic moment= 4.16comparable to the expected value of= 4.24per CoRuO. Using,and high temperature series for, dominant exchange constant/∼ 6 K between the Coon the-sites is estimated. Analysis of the ac magnetic susceptibilities nearyields the dynamical critical exponent= 5.2 and microscopic spin relaxation time∼ 1.16 × 10sec characteristic of cluster spin-glasses and the observed time-dependence of() is supportive of the spin-glass state. Large-loop asymmetry at low temperatures with giant exchange bias effect (∼ 1.8 kOe) and coercivity (∼ 7 kOe) for a field cooled sample further support the mixed magnetic phase nature of this interesting spinel. The negative magnetocaloric effect observed belowis interpreted to be due to the AFM and SG ordering. It is argued that the observed change from positive MCE (magnetocaloric effect) for>to inverse MCE for<observed in CoRuO(and reported previously in other systems also) is related to the change in sign of (∂/∂) vs.data.

摘要

基于我们对交流磁化率和直流磁化强度在温度（T）、磁场（H）和频率（f）方面的依赖性的研究，报道了正常尖晶石CoRuO₄（Co）A[Co³⁺Ru³⁺]BO₄的静态和动态磁性，研究涵盖的温度范围为T = 2 K - 400 K，磁场高达90 kOe。这些研究表明，CoRuO₄在约15.2 K处表现出反铁磁（AFM）转变，同时在略低温度（T₀）约14.2 K附近存在自旋玻璃态。据认为，M主要由占据A位的Co离子的自旋有序性决定，而A位上的Co离子与B位上随机分布的Ru之间的交换相互作用引发了自旋玻璃相，A位上的Co离子处于低自旋非磁性状态。对T < T₀时χ（T，H）测量值的分析用于构建相图，结果表明T随H变化向低温移动，这符合自旋玻璃态的预期，而χ₀几乎与H无关。对于T > T₀，顺磁磁化率（χ）与T数据的分析符合修正的居里-外斯定律，χ = χ₀ + C /（T + θ），其中χ₀ = 0.0015 emu·mol⁻¹·Oe⁻¹，得到θ = 53 K，C = 2.16 emu·K·mol⁻¹·Oe⁻¹，后者得出有效磁矩μeff = 4.16 μB，与每个CoRuO₄预期的μeff = 4.24 μB值相当。利用该结果以及高温级数，估计了A位上Co之间的主导交换常数J / kB ∼ 6 K。对T₀附近的交流磁化率分析得出动态临界指数z = 5.2和微观自旋弛豫时间τ₀ ∼ 1.16 × 10⁻⁸ s，这是团簇自旋玻璃的特征，并且观察到的M（T）的时间依赖性支持了自旋玻璃态。对于场冷样品，低温下的大回线不对称以及巨大的交换偏置效应（约1.8 kOe）和矫顽力（约7 kOe）进一步支持了这种有趣尖晶石的混合磁相性质。在T₀以下观察到的负磁热效应被解释为是由于AFM和SG有序化。有人认为，在CoRuO₄中观察到的从T > T₀时的正磁热效应（MCE）到T < T₀时的逆MCE的变化（之前在其他系统中也有报道）与（∂M / ∂T）对T数据符号的变化有关。