F. Scheibel

Dependence of the inverse magnetocaloric effect on the field-change rate in Mn3GaC and its relationship to the kinetics of the phase transition

We study the dependence of the magnetocaloric effect on the magnetic field-change-rate the first order magnetostructural transition in Mn3GaC by measuring the adiabatic temperature change ΔT at three different time scales: 11 mT s−1, 700 mT s−1, and ∼1000 T s−1. We find that the maximum adiabatic temperature-change of about 5 K is reached in the 11 mT s−1 and 700 mT s−1 rates, whereas for the ∼1000 T s−1-rate the transition lags the change in the magnetic field so that the maximum adiabatic temperature-change is not attained.

Magnetic proximity effect and shell-ferromagnetism in metastable Ni50Mn45Ga5

The present study on magnetic and structural properties of Ni50Mn45Ga5 confirms that structural metastability is an inherent property of Ni50Mn50–xXx Heusler alloys with X as In, Ga, and Sn. The ternary alloy transforms during temper-annealing into a dual-phase composite alloy. The two phases are identified to be cubic L21, Ni50Mn25Ga25, and tetragonal L10 Ni50Mn50. Depending on the annealing temperature, the magnetic-proximity effect giving rise to shell-ferromagnetism has been observed when annealing is carried out under an external magnetic field. The upper and lower remanence values MR+ and MR− have the same sign even at high temperatures. Such alloys can be promising candidates for heat- and magnetic-field-resistant magnetic recording media.

Room-temperature five-tesla coercivity of a rare-earth-free shell-ferromagnet

Ni2MnX-based Heusler (X: main group element), when enriched with Mn, will decompose into ferromagnetic Ni2MnX and antiferromagnetic NiMn when temper-annealed around 650 K. When the starting material is chosen such that the X-composition is about 5 at. % and the annealing takes place in the presence of a magnetic field of about 1 T, the resulting material is a composite of nanoprecipitate strongly pinned shell-ferromagnets with a soft ferromagnetic core embedded in the antiferromagnetic matrix. We show that the shells of the precipitates are so strongly pinned that the estimated field required to fully reorient the spins is in the order of 20 T. We examine in a Ni50.0Mn45.1In4.9 sample the pinning and the magnetic interactions of the precipitate and the matrix with magnetization and ferromagnetic resonance studies carried out in fields ranging up to 14 and 12 T, respectively.

Shell-ferromagnetism in a Ni-Mn-In off-stoichiometric Heusler studied by ferromagnetic resonance

Next to the multifunctional properties of Ni-Mn-based Heusler alloys new functionalities related to shell-ferromagnetism are emerging. To understand in more detail the properties of shell-ferromagnetism we examine a decomposed Ni50.0Mn45.1In4.9 off-stoichiometric compound using magnetic resonance techniques which provides details on magnetic interactions. We find that the ferromagnetic resonance profile of the shell-ferromagnetic state is symmetric for positive and negative fields and is independent of the direction of the field-sweep except for the hysteresis observed at small fields.

Role of developing L10 chemical order on the (0?0?1)-texture formation of (Fe1 ? xCux)Pt films grown on amorphous substrates

We study the technologically important (0 0 1)-texture formation in 10 nm thick (Fe0.9Cu0.1)52Pt48 and, as reference, Fe49Pt51 alloy films. The samples are grown on SiO2(200 nm)/Si(0 0 1) substrates at ambient temperature by pulsed laser deposition. Subsequent rapid thermal processing (RTP) at 650 °C for various time steps drives the initially nanocrystalline and chemically disordered films into the tetragonal L10 phase accompanied by a strong (0 0 1)-texture leading to perpendicular magnetic anisotropy. The fundamental role of the chemical order during short-time annealing as an additional source of strain in the films is experimentally addressed. The structural and magnetic results indicate selective grain growth leading to the (0 0 1)-texture. Strongly prolonged annealing, however, leads to a reorientation of grains towards the (1 1 1)-texture pointing to the increasing importance of surface energies when the initial strain has released.

Annealing-time and annealing-temperature dependencies of the size of Ni-Mn-In shell-ferromagnetic nano-precipitates by Scherrer analysis

Shell-ferromagnetic effects are observed in Ni-Mn-based off-stoichiometric Heuslers decomposed into ferromagnetic precipitates embedded in an antiferromagnetic matrix when the surface-to-volume ratio of the precipitates are sufficiently large. However, since the size of the precipitates have until now not been determined, it is not known which ratios are involved. Here we carry out a Scherrer analysis on decomposed specimens to determine the precipitate-size as a function of decomposition temperature and time.