Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 10(6) ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.

Magnetic frustration effects in artificial kagome arrays of nanomagnets are investigated using x-ray photoemission electron microscopy and Monte Carlo simulations. Spin configurations of demagnetized networks reveal unambiguous signatures of long range, dipolar interaction between the nanomagnets. As soon as the system enters the spin ice manifold, the kagome dipolar spin ice model captures the observed physics, while the short range kagome spin ice model fails.

Large thermal changes driven by a magnetic field have been proposed for environmentally friendly energy-efficient refrigeration 1 , but only a few materials which suffer hysteresis show these giant magnetocaloric effects 2-11 . Here we create giant and reversible extrinsic magnetocaloric effects in epitaxial films of the ferromagnetic manganite La 0.7 Ca 0.3 MnO 3 using strain-mediated feedback from BaTiO 3 substrates near a first-order structural phase transition. Our findings should inspire the discovery of giant magnetocaloric effects in a wide range of magnetic materials, and the parallel development of nanostructured bulk samples for practical applications.2 Magnetocaloric (MC) effects may be parameterized as adiabatic changes of temperature, or isothermal changes of entropy or heat, and have long been used to achieve millikelvin temperatures in the laboratory 12 . More recently, the discovery of giant MC effects near room temperature has led to suggestions for household and industrial cooling applications 1 . However, these giant MC effects arise in only a few materials [2][3][4][5][6][7][8][9][10][11] (Table 1), where strongly coupled magnetic and structural degrees of freedom produce magnetic phase transitions that are accompanied by changes in crystal symmetry 2-10 or volume 11 . It is therefore interesting to explore whether giant MC effects in magnetic materials can be created-rather than merely tuned 16 -via strain. (Table 1). By exploiting a first-order structural phase transition in BaTiO 3 (BTO) substrates, we create giant and reversible MC effects in epitaxial films of LCMO via the entropic interconversion of ferromagnetic and paramagnetic phases, whose coexistence 17,18 we reveal using photoemission electron microscopy (with magnetic contrast from x-ray magnetic circular dichroism) and ferromagnetic resonance.These extrinsic MC effects arise due to a strain-mediated feedback mechanism near the rhombohedral-orthorhombic transition in BTO at ~200 K, i.e. well away from LCMO C T at which the small intrinsic MC effects are seen. 3At temperature T, the isothermal entropy change ) (H S  of a magnetic material due to applied magnetic field H may be obtained via the Maxwell relationprovided that thermally driven changes in measured magnetization M arise due to changes in the magnitude and not the direction of the local magnetization (μ 0 is the permeability of free space, the prime indicates the dummy variable of integration). The Clausius-Clapeyron equation:represents a nominally equivalent indirect method for evaluating S  across first-order phase transitions in terms of the corresponding change in spontaneous magnetization 0 M  and the field-induced shift in transition temperature T 0 . Equations 1 and 2 follow from thermodynamics and do not depend on microscopic details. X-ray diffraction (XRD) of room-temperature LCMO//BTO reveals that the film reflections are weak and broad, and confirms the presence of 90° BTO domains (Fig. 1).The relative population of BTO twins varies between substrates, wi...

We report x-ray magnetic circular dichroism and superconducting quantum interference device magnetometry experiments to study magnetic order and coupling in thin Fe/(Ga, Mn)As(100) films. We observe induced magnetic order in the (Ga, Mn)As layer that extends over more than 2 nm, even at room temperature. We find spectroscopic evidences of a hybridized d configuration of Mn atoms in Fe/(Ga, Mn)As, with negligible Mn diffusion and/or MnFe intermixing. We show by experiment as well as by theory that the magnetic moment of the Mn ions couples antiparallel to the moment of the Fe overlayer.