R. Stubi

Dimensionality crossover in CuMn spin‐glass films

The dynamic properties of Cu (13.5 at. % Mn) spin‐glass films of various thicknesses have been investigated in a superconducting quantum‐interference device (SQUID) magnetometer. The films are produced in a dc‐sputtering system and fabricated in the form of multilayer samples. Utilizing zero‐field‐cooled magnetization and ac‐susceptibility measurements, the time‐dependent susceptibility has been probed over eight decades in time (10−4–104 s). Drastic changes of the dynamics are found upon varying the film thickness from 104 to 20 A. The most significant feature is a crossover from a behavior typical for bulk spin glasses for the 104‐A film, with a finite critical temperature and a critical slowing down that can be accurately described by a conventional power‐law divergence, to a slowing down for the very thin films that obeys a generalized Arrhenius law with a zero‐temperature critical point. Thus, these measurements indicate a crossover from three‐ to two‐dimensional spin‐glass dynamics when one spatial ...

Aging in a two-dimensional CuMn spin glass

Utilizing zero-field cooled magnetization measurements the nonequilibrium dynamics in a 2D spin glass film is investigated. The experiments show that aging is an inherent property of 2D spin glass systems with qualitatively similar features as in 3D systems.

The transition ‘‘back’’ from two to three dimensions

The return from ‘‘quasi‐two‐dimensional’’ to three‐dimensional behavior of the spin‐glass (SG) CuMn(13.5%) is studied in multilayer samples using pure Cu as an interlayer material. We measure how the quasi‐static spin‐freezing temperature T f increases as the interlayer thickness W il is decreased from 30 nm (2D) to 1 nm (3D), keeping the SG layer constant at W SG=4 nm. Alternative interpretations of this behavior have been used in terms of a simple mean‐field RKKY model, the phenomenological scaling theory, and the Fisher and Huse droplet model of SG.

Relaxation of the field cooled magnetisation in 2D Cu(Mn) films

Abstract The relaxation of the field cooled magnetisation of a multilayered 2D Cu(Mn) spin glass film has been investigated in a SQUID-magnetometer. The sample is cooled in a constant magnetic field (10 Oe) from a high temperature, where the magnetisation is at equilibrium, to a temperature below the freezing temperature, T ƒ . At constant temperature, the magnetisation is then found to increase with time at temperatures near T ƒ , showing an initial decrease followed by an increase at long time scales at intermediate temperatures and only decreases with time at lower temperatures. The behaviour, including the surprising downward relaxation away from the thermodynamic equilibrium magnetisation, is qualitatively interpreted in terms of a spin glass domain model.

MULTILAYERED SPIN-GLASS FILMS - SENSITIVE PROBES OF RKKY

A new method that uses superstructures of Cu(Mn) spin glass films separated by metallic interlayers to probe the decay with thickness of the RKKY interaction within the interlayers is discussed.

“Universality” of finite size effects in cumn and agmn spin-glasses

Abstract Recent measurements of the quasi-static spin-freezing temperature, Tf, of thin Cu1-xMnx layers (x = 0.04, 0.07, 0.14) in magnetron sputtered multilayer samples (MS) of CuMn alternated with Cu or Si revealed two different apparently “universal” curves for the ratio T f T f b is the bulk freezing temperature for a given x) for CuMn Cu and CuMn Si MS. We show that cooling the substrates leaves the CuMn Cu MS data unchanged, but moves the n Si MS data closer to the “universal” curve for the CuMn Cu MS show also that T f T f D for AgMn Ag MS agrees with the CuMn Cu MS “Universal” curve.

Dimensionality effects in artificially layered spin-glass structures

Abstract Very large, finite size effects, including evidence of three-dimensional (3D) to two-dimensional (2D) crossover behavior, have been found in both the quasistatic and dynamic properties of thin layers of the spin glasses Cu-Mn and Ag-Mn measured in a multilayer configuration. The most striking feature of the results is the long range of the interactions involved: effects of finite size scaling begin near 100 nm, 3D to 2D crossover occurs on a scale of 10 nm, and spin-glass layers can couple across 10 nm thick metallic interlayers.

Two‐ to three‐dimensional recoupling in AgMn/Cu multilayers

The return from ‘‘quasi‐two‐dimensional’’ to three‐dimensional (3D) behavior of the spin‐glass Ag0.91Mn0.09 is studied in multilayer samples of Ag‐Mn layers of width 4 nm alternated with Cu interlayers of width 1 nm ≤ Wil ≤ 60 nm. For Wil ≳ 30 nm, the SG layers are magnetically decoupled; as Wil decreases below 30 nm, the quasistatic spin‐freezing temperature Tf gradually rises toward the bulk spin‐freezing temperature Tbf. When normalized to Tf/Tbf, the Ag‐Mn data increase with decreasing Wil in a fashion similar to previous data for Cu‐Mn. The data are compared with three different equations.

2D AND 3D SPIN-GLASS DYNAMICS IN THIN CU(MN) FILMS

Abstract Dynamic susceptibility measurements on multilayered Cu(Mn) spin glass films of thickness 40A with interlayers of Cu of thicknesses in the range 10–1200A are reported. The results yield new support for the applicability of domain growth theories to describe spin glass dynamics.