Gallium Substituted "114" YBaFe4O7: From a ferrimagnetic cluster glass to a cationic disordered spin glass

The study of the ferrites YBaFe4-xGaxO7 shows that the substitution of Ga for Fe in YBaFe4O7 stabilizes the hexagonal symmetry for 0.40 < x < 0.70, at the expense of the cubic one. Using combined measurements of a. c. and d. c. magnetization, we establish that Ga substitution for Fe in YBaFe4O7 leads to an evolution from a geometrically frustrated spin glass (for x = 0) to a cationic disorder induced spin glass (x = 0.70). We also find an intermediate narrow range of doping where the samples are clearly phase separated having small ferrimagnetic clusters embedded in a spin glass matrix. The origin of the ferrimagnetic clusters lies in the change in symmetry of the samples from cubic to hexagonal (and a consequent lifting of the geometrical frustration) as a result of Ga doping. We also show the presence of exchange bias and domain wall pinning in these samples. The cause of both these effects can be traced back to the inherent phase separation present in the samples.Comment: 25 pages, 10 figure

Magnetocapacitance effect in perovskite-superlattice based multiferroics

We report the structural and magnetoelectrical properties of La$_{0.7}$Ca$_{0.3}$MnO$_3$/BaTiO$_3$ perovskite superlattices grown on (001)-oriented SrTiO$_3$ by the pulsed laser deposition technique. Magnetic hysteresis loops together with temperature dependent magnetic properties exhibit well-defined coercivity and magnetic transition temperature (T$_C$) \symbol{126}140 K. $DC$ electrical studies of films show that the magnetoresistance (MR) is dependent on the BaTiO$_3$ thickness and negative $MR$ as high as 30% at 100K are observed. The $AC$ electrical studies reveal that the impedance and capacitance in these films vary with the applied magnetic field due to the magnetoelectrical coupling in these structures - a key feature of multiferroics. A negative magnetocapacitance value in the film as high as 3% per tesla at 1kHz and 100K is demonstrated, opening the route for designing novel functional materials.Comment: To be published in Applied Physics Letter

A new intersecting tunnel structure in the AIMIII[PO3(OH)]2 series for AI = Ag, MIII = In : Analysis of structural relationships.

A new indium hydroxyphosphate containing silver, AgIn[PO3(OH)]2, has been synthesized using hydrothermal method. It crystallizes in the P21/c space group with the cell parameters a = 6.6400(2)Å, b=14.6269(6)Å, c=6.6616(4)A, β=95.681(5)°, V=643.82(6)Å3, Z=4. Its three-dimensional framework, built up of comer-sharing PO3(OH) tetrahedra and InO6 octahedra, presents intersecting tunnels running along and [100] directions, in which the Ag+ cations are located. The presence of hydroxyl groups has been confirmed from IR spectroscopy studies and hydrogen atoms were located from the single crystal X-ray diffraction study. The structural relationships with the other compounds of general formula AΙΜΙΙΙ[PΟ3(OH)]2 are analyz

Magnetic-history-dependent nanostructural and resistivity changes in Pr0.5Ca0.5Mn0.98Cr0.02O3

We show that nanostructure and resistivity of Pr0.5Ca0.5Mn0.98Cr0.02O3 are sensitive to whether the sample is zero-field-cooled (ZFC) of field-cooled (FC) either in the 'self magnetic field (H = 2 T)' of the electron microscope or under the external magnetic field of 2 T. FC resistivity at H = 2 T is lower than ZFC values below 140 K. The average value of the chare-orbital modulation vector (q = 0.44) of the FC crystallites is lower than that of the ZFC cystallites (q = 0.48) and the FC crystallites exhibit numerous defects like discommensuration, dislocations and regios with loss of superstructures compared to the ZFC crystallites.Comment: 7 pages, 3 figure

Parental Ptsd, Emotion Regulation, And Behavior Problems In Toddlerhood: Unique Associations Among Families In Urban Poverty

Parental posttraumatic stress disorder (PTSD) has been shown to negatively impact children’s socioemotional development (Schwerdtfeger et al., 2014) and increase children’s risk for later psychopathology (Scheeringa & Zeanah, 2008; Yehuda, Halligan, & Bierer, 2001). Less is known about this topic among minority and poor mothers and fathers of toddlers, and the critical role parents’ emotion regulation may play in mediating the associations between PTSD and toddlers’ socioemotional problems (Beck et al., 2009). Parental emotion dysregulation has been linked with children’s socioemotional problems (Coyne & Thompson, 2011), especially during toddlerhood when children are beginning to learn how to regulate their own emotions (Kopp, 1989). Evaluating both mothers’ and fathers’ PTSD, emotion regulation, and child behavior problems during toddlerhood is particularly important among urban populations due to high risk of trauma exposure (Evans & English, 2002). The current study aimed to examine internalizing and externalizing behavior problems in toddlers from low-income families, evaluating whether and how mothers’ and fathers’ PTSD, emotion regulation, and parenting are associated with toddler behavioral problems. It was hypothesized that the relationship between parents’ PTSD and toddlers’ internalizing and externalizing problems will be mediated by parents’ emotion regulation and parenting quality. The current study describes data from a broader study of socioemotional development of toddlerhood among urban families (N=96). Mothers and fathers reported on their own PTSD symptoms (PDS; Foa et al., 1997), depression (CES-D; Radloff, 1977), emotion regulation (EDS, Conklin et al., 2006), and their toddlers’ behavior problems (CBCL; Achenbach & Rescorla, 2001). Parenting quality was coded based on observational data from a family drawing task, during which families drew pictures of happy and sad times they have had as a family. Children’s internalizing and externalizing problems were calculated by averaging the CBCL scores reported by both parents. Primary analyses were conducted using Hayes PROCESS macro for multiple mediation (model 6; Hayes, 2013), controlling for maternal and paternal depression, and cumulative demographic risk. Findings indicated that (1) both mothers’ and fathers’ emotion regulation and depression, but not PTSD and parenting, were the main parental factors linked to higher internalizing behavior problems in toddlers, and only mothers’ cumulative demographic risk was significantly associated with toddlers’ externalizing behavior problems; (2) the associations between parental PTSD and child behavior problems was not mediated through emotion regulation and parenting; (3) fathers’ symptoms of emotion dysregulation and depression were as equally important in predicting toddler behavior problems as mothers’ emotion dysregulation and depression; (4) parental PTSD, emotion dysregulation, and depression were more strongly associated with toddlers’ internalizing problems than their externalizing problems. Findings provide support for the negative impact of maternal and paternal emotion dysregulation, depression, and cumulative demographic risk on toddler internalizing and externalizing problems among low-income families and offer insight into essential avenues to implement interventions. Although parents’ PTSD symptoms may have an impact on toddlers’ behavior problems, their emotional dysregulation plays a more significant role. The focus mediator, paternal emotion regulation, appears to be a concrete target for clinical assessment and treatment

Ethnicity, Culture, And Mental Health Among College Students Of Middle Eastern Heritage

Depression is a significant mental health issue in American college students. However, as is the case for other minority students, this topic has been little studied in students of Middle Eastern background. Stigma and negative attitudes toward seeking mental health services are a big part of Middle Eastern culture, which reduces the chances that this population will seek treatment when they need it. In addition, it is important to study the relationship between ethnic identity and psychological functioning, because ethnic identity could serve as a protective factor against depression in persons of Middle Eastern descent. A strong cultural identity is thought to have that effect for persons of other minority groups in this country. The current study explored depression symptoms in Middle Eastern, African American, and Caucasian college students. No group differences were found in level of depression symptoms. As expected, Middle Eastern college students had more negative attitudes toward seeking mental health services than African American and Caucasian students. Among the African Americans and Caucasians, stronger ethnic identity was associated with lower presence of depression symptoms when controlling for gender, age, and social desirability; however, this relationship was not significant among the Middle Eastern and African American students. Research on minority college students could provide greater insight into their current needs, allowing policy makers to implement appropriate interventions for minority individuals. These findings indicate that Middle Eastern students may have characteristics related to their mental health that are not well represented by most research in the more commonly studied ethnic groups among American college students

Toward modelling of frictional ignition

International audienceThis work is part of a European sponsored project named MECHEX (GRD2-2000-30035) which aims at providing a new insight and data about the ignition hazard induced by mechanical contacts classically termed as "grinding", "friction" and "impact" so that some sort of classification of mechanical equipments against this specific hazard could be issued. "Friction" and "grinding" might be understood as continuous mechanical solicitation whereas "impact" would be referred to as an instantaneous action such as that of a flying object striking freely on a fixed target. Within that scope, we undertook a detailed physical analysis of possible ignition mechanisms on the basis of precise measurements of hot spots, temperatures and fragments and tried to link them to the thermomechanical properties of the contacting bodies