Contents lists available at ScienceDirect Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm Path dependent magnetic states and evidence of kinetically arrested states in Nd doped LaFe 11.5 Al 1.5 Pallab Bag, R. Nath ⁎ School of Physics, Indian Institute of Science Education and Research, Thiruvananthapuram 695016, India ARTICLE INFO Keywords: Rare-earth metal First order phase transition Phase coexistence Magnetic glass Kinetic arrest Specific heat ABSTRACT First order antiferromagnetic to ferromagnetic transition and path dependent magnetic states in La 1-x Nd x Fe 11.5 Al 1.5 for x∼0.1 are studied at low temperatures via powder x-ray diffraction, magnetization, and specific heat measurements. X-ray diffraction measurements suggest that around 8% of high temperature antiferromagnetic phase is converted to ferromagnetic phase at low temperatures in zero field cooling. A systematic study of temperature and magnetic field dependent magnetization measurements show a non- monotonic variation of upper critical field and re-entrant antiferromagnetic-ferromagnetic-antiferromagnetic transition while warming at an applied magnetic field under zero-field-cooled condition. This has been interpreted in the framework of kinetic arrest model for first order magnetic transition. It is also found that the antiferromagnetic phase is in the non-equilibrium state and behaves as a glass-like magnetic state at low temperatures. The specific heat in field-temperature space is studied and found to have a lower electronic contribution for the non-equilibrium antiferromagnetic state, compared to the equilibrium ferromagnetic state in this compound. 1. Introduction Recent magnetic studies of the doped itinerant electron metamag- netic LaFe 13 compound have revealed wide varieties of interesting properties such as giant magnetocaloric effect [1–22], giant barocaloric effect [8,10,23], giant magnetostriction [24,25] etc due to the onset of a first order magnetic transition. Though LaFe 13 does not exist as it is, but substitution of Al or Si at the Fe site, stabilizes in a NaZn 13 -type cubic structure [24]. For LaFe 13-x Al x , the ground state is antiferro- magnetic (AFM) in the range x 1.04 ≤ < 1.82, soft ferromagnetic (FM) for x 1.82 ≤ < 4.94, and a mictomagnetic state for x 4.94 < < 7.02 [24]. The ground state of LaFe 13-x Al x for the above x-ranges can be tuned from AFM to FM by substituting rare earth elements like Ce/Pr/Nd at the La site [11,12,15,20,22,26,27], Si at the Al site, Co/Mn at the Fe site [5,13,14,19,22,23,28] and with interstitial addition of H/C/N/B atoms [2,4,6,15,16,21,22,29–32]. With increasing temperature, the compounds having FM ground state show a first order FM-AFM transition followed by a second order AFM to paramagnetic (PM) transition or only a first order FM-PM transition depending on the doping concentration [3,6,7,12,15,16,19,21,22,24–27,31–34]. The first order magnetic transition in these systems are accompanied by around 1% iso-structural change in volume where the low temperature FM state has the higher volume than the high temperature AFM (or PM) state [24,35,36]. Moreover, the FM state has the higher electronic contribution or the lower resistivity than that for the AFM state [12,24,27,28,32]. The first order magnetic transition in this series can be explained on the basis of the itinerant electron magnetism model, which basically depends on the Fe-Fe distance and its coordination number [24,25,36,37]. The magnetism in these systems arise due to Fe, which have two crystallographically inequivalent sites 8b [Fe(1)] and 96i [Fe(2)] [24,37]. Neutron diffraction measurements suggest that the FM clusters/icosahedra composed of twelve Fe(2) and one Fe(1) sites are coupled ferromagnetically in the (100) plane and antiferromagnetically between the planes [35,37]. The first order magnetic transition is also strongly dependent on external perturbations such as magnetic field and external pressure [3,8,13,15,16,21,24,26,31,33,34,38]. It is reported that the ground state of LaFe 11.5 Al 1.5 is AFM and it shows a field induced FM state at low temperatures [12,16,21]. With Nd doping (at the La site), the FM state is stabilized when Nd concentration exceeds 20%. Below this concentration, there exists a strong AFM – FM competition, as inferred from the anomalous temperature and field-dependent magnetic behaviour [11,12,22,26]. The magnetization data in zero-field-cooled cycle measured while warming at an applied field (ZFCW) shows two transitions (namely AFM to FM followed by FM to AFM) whereas, the field-cooled-cooling http://dx.doi.org/10.1016/j.jmmm.2016.11.129 Received 30 September 2016; Received in revised form 28 November 2016; Accepted 28 November 2016 ⁎ Corresponding author. E-mail address: rnath@iisertvm.ac.in (R. Nath). Journal of Magnetism and Magnetic Materials 426 (2017) 525–529 0304-8853/ © 2016 Published by Elsevier B.V. Available online 30 November 2016 crossmark