Stoner enhanced paramagnetic inﬂuence on superconductivity in a superconductor/metallic heterostructure S.J. Ray a,⇑ , S.J. Lister a , S.L. Lee a , Olav Hellwig b , J. Stahn c a SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS, United Kingdom b San Jose Research Center, Hitachi Global Storage Technologies, 650 Harry Road, San Jose, CA 95120, USA c Laboratory for Neutron Scattering, ETH Zurich & Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland article info Article history: Received 28 September 2012 Received in revised form 16 January 2013 Accepted 29 January 2013 Available online 14 February 2013 Keywords: Thin ﬁlm PNR Coexistence of Superconductivity and Magnetism Superconductivity Magnetism Stoner enhancement abstract The unusual magnetic behaviour of a Pd/Nb 67 Ti 33 /Pd heterostructure was investigated using polarised neutron reﬂectivity technique. On application of a large in-plane magnetic ﬁeld, Stoner enhanced para- magnet Pd was found to inﬂuence the magnetic state of the Nb 67 Ti 33 layer both above and below the superconducting transition temperature T c signiﬁcantly. Unlike the case of a conventional proximity effect for a superconductor/metallic heterostructure, the pair correlation in the superconducting state has been found to be more stable in the higher ﬁeld limit compared to its low ﬁeld counterpart, possibly signatur- ing a ‘novel’ coupled state in the system. The superconducting state in Nb 67 Ti 33 has been found to be dia- magnetic in nature at all the ﬁelds that can be ﬁtted using a Meissner kind of behaviour in the high ﬁeld limit. The magnetic properties of Pd and Nb 67 Ti 33 are in excellent agreement with those measured using bulk magnetisation measurements. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The magnetic behaviour of superconducting thin ﬁlms are of huge interest mostly in multilayered structures in combination with other magnetic layers (ferromagnetic, normal metal, etc.) [1,2]. In the thin ﬁlm geometry, the behaviour of a superconducting material can be signiﬁcantly different from its bulk counterparts because of reduced dimensionality. The 3-dimensional supercon- ducting behaviour often changes to 2-dimensional nature in a superconducting thin ﬁlm when the thickness is reduced below a certain critical limit [3,4]. In the presence of a normal metal (N) near a superconductor (S), the physical properties of both materials change near the interface. At the superconductor (S)/normal (N) metal interface, Cooper pairs penetrate and decay into the normal metal over a characteristic distance  L T ¼ ﬃﬃﬃﬃﬃﬃﬃﬃﬃ D=T p , called as the thermal diffusion length where D is the diffusion constant and T is the absolute temperature [1]. This has been experimentally ob- served in the case of a S/N bilayer, where T c decreases monotoni- cally with an increase in the normal layer thickness (d N ) due to enhanced Cooper pair breaking [5]. This is called as the proximity effect [6] in the case of a S/N structure. In the case of proximity ef- fect for a superconductor (S)/ferromagnet (F) heterostructure, the decay of the pair correlation will be modulated in the F layer under the inﬂuence of the ferromagnetic exchange ﬁeld and will show a damped oscillatory behaviour [1]. In the recent times, continued theoretical and experimental interests have grown in this area of research to understand the behaviour of superconducting thin ﬁlms and multilayered S/N sys- tems. While typically macroscopic experimental probes like mag- netisation and transport measurements [7,8,5] are used for these investigations, less has been done using microscopic probes like neutrons in these systems. The technique of polarised neutron reﬂectivity (PNR) is an ideal method to probe the structural and magnetic behaviour of superconducting thin ﬁlms and S/F multi- layers [9–15,4]. In a PNR experiment, spin polarised neutrons in their ‘up (")’ and ‘down (;)’ spin eigen states (with respect to the direction of the applied magnetic ﬁeld) arrive at the sample surface and specular reﬂection of the neutrons are detected which in the case of a multilayered structure provide information regarding the structural and magnetic behaviour of the heterostructure. The PNR technique provides large spatial sensitivity (10 Å) to measure microscopic variation of the magnetic ﬂux proﬁle in a multilayered structure perpendicular to the plane of the ﬁlm which have been successfully used to measure the magnetic behaviour of thick [10,11] and thin [12,13] superconducting ﬁlms, inﬂuence of ferromagnetism on superconductivity in a F/S heterostructure [14,15] for an applied ﬁeld in the plane of the ﬁlm. 0921-4534/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.physc.2013.01.019 ⇑ Corresponding author. E-mail address: ray.sjr@gmail.com (S.J. Ray). Physica C 487 (2013) 67–71 Contents lists available at SciVerse ScienceDirect Physica C journal homepage: www.elsevier.com/locate/physc