Magnetocaloric effect in R2Ti3Ge4 (R = Gd, Tb and Er) Compounds

Heat capacity of polycrystalline R2Ti3Ge4 (R = Gd, Tb and Er) compounds (Orthorhombic, Sm5Ge4-type, Space group Pnma) has been studied in the temperature range of 1.8 K to 300 K in various applied magnetic fields. The compounds with magnetic lanthanide elements show interesting low field magnetism intrigued by possible presence of competing antiferromagnetic and ferromagnetic interactions. The magnetocaloric effect in these compounds is estimated from the field dependent heat capacity data. The magnetic entropy change and the adiabatic temperature change in the vicinity of the magnetic transition are found to be significant.Comment: 12 pages incl 3 figures, submitted to Journal of Applied Physic

Magnetic-field induced melting of long-range magnetic order akin to Kitaev insulators in the metallic compound Tb5Si3

There have been constant efforts to find exotic quantum spin-liquid (QSL) materials. Some of the transition metal insulators dominated by the direction dependent anisotropic exchange interaction (Kitaev model for honeycomb network of magnetic ions) are considered to be promising cases for the same. In such Kitaev insulators, QSL is achieved from the zero-field antiferromagnetic state by the application of magnetic field, suppressing other exchange interactions responsible for magnetic order. Here, we show that the features attributable to long-range magnetic ordering of the intermetallic compound, Tb5Si3 (T_N= 69 K), containing honey-comb network of Tb ions, are completely suppressed by a critical applied field, H_cr, in heat-capacity and magnetization data, mimicking the behavior of Kitaev physics candidates. The neutron diffraction patterns as a function of H reveal that it is an incommensurate magnetic structure that gets suppressed, showing peaks arising from multiple wave vectors beyond Hcr. Increasing magnetic entropy as a function of H with a peak in the magnetically ordered state is in support of some kind of magnetic disorder in a narrow field range after H_cr. Such a high-field behavior for a metallic heavy rare-earth system to our knowledge has not been reported in the past and therefore is intriguing.Comment: Journal of Physics: Condensed Matter, in pres

Large magnetoresistance in intermetallic compounds R2Mn3Si5 (R = Tb, Dy and Ho)

Magnetization (M) and magnetoresistance (MR) measurements on polycrystalline R2Mn3Si5 (R = Tb, Dy and Ho) compounds (tetragonal, space group P4/mnc) have been carried out in the temperature range of 2 K-300 K, in various applied fields. Both, the rare earth and the Mn, are found to carry magnetic moments in these compounds. Mn has two sub-lattices (Mn1 and Mn2) that order magnetically at two different temperatures. Rare earth and Mn1 moments order ferromagnetically at TC1 whereas Mn2 is found to magnetically order at TC2 (TC1 = 89 K, 86 K, 78 K and TC2 = 18 K, 34 K, 16 K for R = Tb, Dy and Ho compounds, respectively). Magnetoresistance measurements reveal large negative MR values of about 50 % near TC2 at 9 T in all these compounds. This giant magnetoresistance is attributed to the spin-dependent scattering effects, competing exchange interactions and the layered structure of these compoundsComment: Submitted to Europhys. Let

Magnetocaloric properties, magnetic interactions and critical behavior in Ho6(Fe,Mn)Bi2 intermetallics

Four polycrystaline Fe2P-type Ho6(Fe,Mn)Bi2 intermetallic compounds (space group , No. 189, hP9) have been studied using magnetic techniques in order to explore their ability as magnetocaloric materials, and study the critical behavior of the paramagnetic (PM) to ferromagnetic (FM) transitions to obtain a deeper understanding of the range of the magnetic interactions. The obtained critical exponents β, γ and δ for the four compounds studied (Ho6MnBi2, Ho6FeBi2, Ho6(Mn0.5Fe0.5)Bi2, Ho6(Mn0.75Fe0.25)Bi2) point to long-range order interactions, as they are close to those of the Mean Field Universality class. All of the compounds show relevant magnetocaloric properties over a very broad temperature range, limited by the PM-FM transition and a spin-reorientation one, well separated in all cases. They present very high values of the refrigerant capacities (from 520 J/kg to 709 J/kg at 5 T), good magnetic entropy changes (from 3.4 to 5.7 J/(kgK) at 5 T), and a flat and wide temperature span for the working temperature range (nearly 200 K for Ho6MnBi2, 80 K for Ho6FeBi2 at 5T). The change in properties with composition proves that the magnetocaloric properties can be tuned in Fe2P-type compounds to accommodate different refrigeration applications. Finally, the magnetocaloric scaling laws have been successfully tested and universal curves for the magnetic entropy change have also been obtained in the PM-FM transition region.This work has been supported by Universidad del País Vasco UPV/EHU (GIU16/93)

Magnetocaloric properties and unconventional critical behavior in (Gd,Tb)6(Fe,Mn)Bi2 intermetallics

The magnetic and magnetocaloric properties of the intermetallic family (Gd,Tb)6(Fe,Mn)Bi2 have been studied from 2 K to temperatures above the respective Curie temperatures TC. The substitution of Gd by Tb (Gd6FeBi2, Gd3Tb3FeBi2, Tb6FeBi2) tunes TC in the range 350-250 K and favors the apparition of a metamagnetic transition at very low temperature (below 10 K) from a complex magnetic state to a ferromagnetic one, as well as a spin reorientation transition below Tm = 72 K. As a consequence, an important inverse magnetocaloric effect (IMCE) appears below 20 K and an interesting direct magnetocaloric effect (DMCE) appears over a wide temperature span between TC and Tm with maxima at those temperatures. The partial substitution of Fe by Mn in Tb6Fe0.5Mn0.5Bi2 shifts these effects upwards in temperature while expanding the region of the direct magnetocaloric effect between 70 and 400 K. The combination of adjoint IMCE and DMCE as well as the wide span of the latter shows that tuning this family allows to locate the magnetocaloric effect in different regions of interest. The critical behavior of the PM-FM transitions has been studied obtaining the critical exponents α, β, γ, δ and checking that the respective magnetocaloric effects also scale with the critical parameters n and δ. The transition in Gd6FeBi2 belongs to the Heisenberg universality class with deviations due to magnetocrystalline anisotropies; the critical exponents for Gd3Tb3FeBi2 (in agreement with the Mean Field model) suggest the presence of long range order magnetic interactions, while Tb6FeBi2 and Tb6Fe0.5Mn0.5Bi2 present an unconventional critical behavior aligned with long range order interactions.This work has been supported by Universidad del País Vasco UPV/EHU (project GIU19/305) and the Russian Fund for Basic Research (project N° 20-03-00209-a). A. Herrero thanks the Department of Education of the Basque Government as grantee of the programme “Programa Predoctoral de Formación de Personal Investigador No Doctor”. The authors thank for technical and human support provided by SGIker of UPV/EHU

Circulating microRNAs in lung cancer: prospects for diagnosis, prognosis, and prediction of antitumor treatment efficacy

The review considers the main techniques to extract microRNA (miRNA) from various biological fluids (in particular, the serum and plasma), approaches to the analysis of miRNA concentration and composition, and methods to normalize the results in data analyses. Advantages and drawbacks of the methods are described. Special attention is given to circulating miRNAs, which can be used as markers for minimally invasive diagnosis, prediction of antitumor treatment efficacy, and disease prognosis in lung cancer. The review discusses the prospects and limitations that arise as the clinical significance is evaluated for miRNAs as potential tumor markers and a better understanding is gained for the roles various miRNAs play in the pathogenesis of lung cancer